B23D-1575
Plant Biodiversity Positively Affects Short-term Soil Carbon Storage in Experimental Grasslands
Increasing atmospheric CO2 concentration and related climate change have engendered much interest in the potential of soils to sequester carbon. Here, the link between plant biodiversity and soil carbon storage was investigated in "The Jena Experiment", a managed grassland experiment on a former agricultural site. Biodiversity gradients ranged from 1 to 60 species belonging to 4 functional groups. Stratified soil samples were taken to 30 cm depth from 86 plots in 2002, 2004 and 2006, and organic carbon concentrations were determined. Land use change induced a decrease in carbon stocks from 7.3 kg C m-2 in 2002 to 6.7 kg C m-2 in 2004, but by 2006 carbon stocks had recovered to 7.8 kg C m 2. Organic carbon concentration strongly increased in the top 5 cm of soil but decreased below 20 cm depth as a short-term effect of land use change. The average concentration increase was 1.4 g C kg 1 soil after 2 years and 2.4 g C kg 1 after 4 years in the upper 5 cm and was significantly correlated with sown species number and number of functional groups. Although increasing species diversity resulted in higher biomass production, statistical analyses revealed that species diversity per se was more important than biomass production for changes in soil carbon. Below 20 cm depth the presence and proportion of one functional group - tall herbs - significantly reduced carbon losses. Our short-term analysis suggests that inherited soil carbon degrades with a turnover time of ~10 years and is simultaneously replaced by carbon from the extant ecosystem. Overall carbon stocks are determined by land use and management. However, species richness and certain functional traits can accelerate the build-up of new pools. Consequently, higher biodiversity in a given land use and climate system mitigates carbon losses in the short-term and might lead to higher carbon sequestration in the long-term.
B23D-1576
The Importance of Vertical Heterogeneity in Soil Organic Matter for Determining Soil Respiration and Carbon Sequestration With Global Ecosystem Models
A major shortcoming of many current global models simulating soil carbon processes is the lack of consideration for the non-uniform vertical distribution of soil organic matter (SOM). By treating the soil as a homogeneous ´bucket´ of carbon, with constant properties and dynamics in time and depth, a number of processes and interactions are ignored which can strongly affect biochemical cycles in the soil and the whole ecosystem. Firstly, when root and microbial respiration do not occur close to the soil surface, the gradient of temperature, moisture and oxygen availability should be considered in order to correctly determine the CO2 production and efflux. Secondly, carbon sequestration often occurs in the deep soil (Rumpel et al., 2002), either because recalcitrant SOM fractions are transported downward or because of unfavorable conditions at depth. The latter reason includes a lack of fresh energy-rich litter, which is related to the so-called ‘priming' effect (Fontaine et al., 2004), referring to the increase of old SOM decomposition when fresh litter is added. We propose that ignoring vertical heterogeneity in soil can lead to errors in predictions of global models and present the first results of a new soil-process model which includes the vertical heterogeneity of organic matter, temperature and moisture, as well as the mechanisms leading to carbon stabilization in the subsoil. This model is to be applied at a global scale, in global ecosystem models. We show that in many cases the vertical heterogeneity of SOM has an important effect on the carbon cycling in soil and should not be ignored.
B23D-1577
Temporal and spatial variations of soil CO2 flux over a crop field in Nebraska
Soil CO2 flux (Fc) is the largest component of the ecosystem carbon balance. It is also an important piece of information in the study of soil carbon storage potential and soil carbon dynamics. Fc has a strong temporal variation over the course of a day or a season because of changes in soil temperature, soil moisture, above ground vegetation physiological activities, and other driving variables. It also shows a strong spatial variation because of high heterogeneity of soil properties in the field. To understand the temporal and spatial variations of Fc over an agricultural field, we used an automated soil CO2 flux system (LI-8100/8150, LI-COR Biosciences, Lincoln, Nebraska, USA) to continuously measure the Fc at 16 different locations in a soybean field for the entire growing season in 2006. The automated system is a nonsteady state closed-chamber system. Our results show that Fc varied from 0.4 to 8.0 μmol m-2s-1 depending on the time of season, the soil temperature and the moisture content. The Coefficient of Variation (CV) over the 16 locations was in the range of 20-60% for the major portion of the time. Rain events could increase CV to more than 100% because Fc responds to rain events differently depending on the amount of residual material at the soil surface. Manual measurements at weekly or longer time intervals often fail to accurately estimate the total soil CO2 flux. Our data show that weekly measurements could have ±5% error in total soil CO2 flux as compared with continuous measurements. Biweekly or monthly measurements could have ±13%, ±25% errors, respectively. Our result strongly suggests that high spatial and temporal resolution data is essential in accurately estimating the total soil CO2 flux and in understanding the soil carbon dynamics and how biological and environmental variables regulate the flux. Also some critical requirements in making chamber-based soil CO2 flux will be discussed.
B23D-1578
Feedback of Ambient Air CO2 Concentration on Soil CO2 Efflux
Soil CO2 flux (Fc) is driven largely, or in part, by the CO2 concentration gradient across the soil surface. We show that under calm and warm night-time conditions, ecosystem respiration can lead to elevated ambient air CO2 concentration (Ca) above the soil, which suppresses Fc, as expected from diffusion theory. We hypothesize that on warm and calm nights prolonged suppression of Fc has the effect of capping the soil, and leads to elevated soil CO2 concentrations (Cs). When the atmosphere becomes unstable at sunrise, or when the friction velocity (U*) increases, this cap is removed by replacing air that has elevated Ca with ambient air characteristic of the well-mixed atmosphere. This can occur quite rapidly producing a large gradient between Cs and Ca, which enhances Fc, especially at sunrise. Elevated Fc can persist for one to two hours, apparently until the soil CO2 concentration profile readjusts. We conducted a series of experiments at two field sites with different soil and vegetation types, in which we investigated the impact of ambient CO2 concentration on Fc. Nearly continuous measurements of night-time Fc from the two sites demonstrated that Fc was negatively correlated with changes in Ca, suggesting Fc was suppressed under high Ca due to the reduced CO2 diffusion gradient. This has the effect of increasing CO2 storage in the soil. At sunrise, increased turbulence caused a rapid drop in Ca and an increase in Fc that preceded any increase in soil temperature, and persisted for one to two hours. We used the LI-6400 to test the hypothesis that capping the soil with elevated Ca would lead to increased Fc after Ca returned to normal levels. We allowed the chamber headspace CO2 concentration to rise to various levels above ambient, whereupon we scrubbed the chamber air quickly back to ambient and measured Fc at ambient Ca. Measured Fc increased with increasing CO2 concentration in the headspace prior to measurement, as predicted by a diffusion-based mechanism. Wind-induced pressure pumping was not involved. This has important implications both for chamber measurements and for ecosystem respiration. Our results suggest that respired CO2 can accumulate in the soil profile under calm conditions. CO2 accumulated in the soil can slowly flush out when Ca returns to the atmospheric background level as the atmosphere becomes unstable. It is likely to take much longer to flush out CO2 accumulated in the soil profile than to exchange CO2 accumulated in the plant canopy. This diffusion-based process might provide an explanation, in addition to U*-dependent night-time flux and pressure pumping, for the abnormally high ecosystem respiration rate at sunrise sometimes observed by the carbon flux community. Flechard, et al. (2007, Temporal changes in soil pore space CO2 concentration and storage under permanent grassland. Agric. Forest Meterol. 142:66 ) present a similar argument, although they suggest wind-induced pressure pumping as the primary mechanism moving CO2 out of the soil and into the atmosphere.
B23D-1579
Climate Effects on Soil Carbon Sequestration in a Grass, Oak and Conifer Ecosystem of California
Dissolved organic matter (DOM) leaching from decomposing detritus accumulated above mineral soils is an important carbon (C) and nitrogen (N) flux that influences biogeochemical processes, C sequestration and the health of individual ecosystems. Previous studies have shown that the main process controlling DOM mobility in soils is sorption in the mineral horizons that adds to stabilized organic matter pools. The objective of this study was to determine the effect of temperature and incubation time on DOC and DON biodegradation and sorption in the mineral soil. Surface litter from a grass, oak and a conifer site were leached with deionized water for 5, 15 or 96 hours at 4, 20 or 30oC. The resulting DOM solutions were characterized using 13C NMR, XAD-8 resin and UV-vis spectroscopy. The biodegradable fraction (BDOC) of these solutions was quantified using inoculum from A horizon soils. The DOM solutions were also used in sorption experiments on A horizon soils. Supernatant from the A horizon sorption experiment was then used in a sorption experiment on Bt horizon soils and analyzed for BDOC using Bt horizon inoculum. The ability of the soils to adsorb DOC increased with increasing aromaticity in the DOC solution. Therefore, conifer DOM exhibited greater sorption than oak and grass DOM due to higher aromaticity. In all horizons, we observed net release of indigenous OM when OM-free solution was added. Net release of OM was greatest from the soils from the pine site, which had the greatest OM content among the soils we studied. ***Results still pending***
B23D-1580
Modeling Forest Soil Organic Carbon of Japanese Forest Soils
This paper presents results of regional application of the CENTURY ecosystem model to Japanese forests. Global and regional evaluation of organic carbon stored in forest soil and greenhouse gases emissions from forest soils are important (e.g., the Kyoto protocol). Our goal is to develop a biogeochemical model that can simulate carbon dynamics in Japanese forests at both site and regional scales. We applied the CENTURY model to Japanese forest at 1 km × 1 km resolution (about 240000 grids) and compared the outputs with data of several datasets and reviewed results (net primary production, soil organic carbon, surface litter, soil respiration). This paper will present an overview of our modeling of organic carbon stored in Japanese forest soils and some preliminary results relating to carbon dynamics. Also, we will introduce an ongoing project of forest soil inventory in Japan, in which 3200 plots all over Japan will be surveyed.
B23D-1581
Temporal Changes in Soil Carbon Storage Across a Managed Red Spruce Forest Chronosequence Reveal Low Carbon Stabilization Capacity of a Podzol Soil
Forest harvesting alters the long term balance of inputs and outputs, potentially affecting the quantity of carbon stored in a forest soil. Using a successional chronosequence, we sampled the top 50 cm of mineral soil in a mature old growth forest, an immature old growth forest, a 45 year old clearcut, a 15 year old clearcut, and a recent clearcut all separated by no more than 5 km and differing only in their time since harvest. Soils sampled from each site were subjected to a density fractionation method to separate soil carbon into three fractions: a free light fraction, an intra-aggregate or occluded light fraction, and a mineral associated heavy fraction. Fractions were analyzed for % C and, δ13C, and carbon storage was estimated for each fraction. Temporal trends in storage for the whole soil and all fractions described using a gamma function, showed that losses in the whole soil reached a minimum 30 years post harvest, at which point they were approximately 50% of the reference condition. In each of the three fractions losses were of a similar magnitude but minima occurred at different times post harvest. Losses were greatest below the dominant rooting zone (>20 cm) and in the mineral associated heavy fraction and stable isotopic signatures suggest accelerated decomposition as the mechanism of loss. Our findings are consistent with a low stabilization capacity and suggest that a significant proportion of the soil carbon pool in the top 50 cm of mineral soil is capable of cycling on decadal time scales in response to environmental perturbations.
B23D-1582
Oxidation of humic substances supports denitrification reactions in agricultural soils.
Humic substances (HS) are a ubiquitous, recalcitrant, and diverse class of compounds arising from degradation and condensation of plant and microbial biopolymers. Many bacteria oxidize hydroquinones within humic substances to their quinone analogs, providing electrons for respiratory processes such as nitrate reduction. Microbial hydroquinone oxidation contributes to the redox state of HS and supports denitrification, which may be of import to agricultural soils where nitrate retention is critical and HS are prevalent. Most probable number counts were performed on soils collected from a Nebraska farm, with the model humic hydroquinone 2,6- anthrahydroquinone disulfonate (AHDS) serving as an electron donor and nitrate as the electron acceptor. Results indicated that AHDS oxidizing, nitrate reducing bacteria were present in soils from bluegrass fields (104 cells/g) and aspen groves (106 cells/g), as well as in plots of corn (106 cells/g), and soybean treated (106 cells/g) and un-treated (105 cells/g) with pig slurry. These results demonstrate that microorganisms participating in the proposed metabolism are prevalent within agricultural soils. Upflow glass columns were constructed, containing a support matrix of glass beads amended with 10% w/w soil from the corn plot previously mentioned. All columns were subjected to a continual flow of phosphate-buffered water amended with sodium nitrate. Above the point source for nitrate injection, phosphate-buffered water containing electron donor treatments were continually injected. The impacts of electron donor treatments (no donor, oxidized HS, reduced HS, and acetate) on denitrification and other geochemical parameters were observed. Column studies were able to resolve effects of electron donor treatment both spatially as a function of distance from the injection point source, and temporally, as a function of time of donor treatment. Four sample ports in each column were routinely analyzed for concentrations of nitrate, nitrite, Fe(II), and humic-born hydroquinones. All data were analyzed with respect to dilution factors obtained through analysis of a conservative bromide tracer present in electron donor medium. Addition of oxidized HS, reduced HS, and acetate all resulted in significant loss of nitrate from the columns. Significant nitrite accumulation was not observed. Of all the electron donor treatments, reduced HS, enriched for hydroquinone-containing functional moieties, supported the greatest degree of denitrification. The participation of excess hydroquinones in denitrification accounted for approximately 104% of the difference in nitrate reduction between reduced and oxidized HS treatments. This electron balance allowed for assignment of respiratory activity due to hydroquinone oxidation, rather than degradation of humic substances or associated electron-donating compounds. These results suggest that denitrification reactions catalyzed by microbial oxidation of reduced HS may be prevalent in agricultural soils. Likewise, these results demonstrate for the first time that respiratory behavior due to hydroquinone oxidation, as well as impact upon local geochemistry, can be analyzed in complex flow-through model systems.
B23D-1583
The Fate of Microbial Groups in Tropical and Temperate Forest Soils
This research investigates the importance of microbial biochemistry to carbon (C) humification pathways in two climatically different forested ecosystems, Blodgett forest (BF), a temperate forest in the Sierra Nevada and Luquillo forest (LF), a tropical forest in Puerto Rico. 13C enriched tropical and temperate species from four microbial groups (fungi, actinomycetes, bacteria gram (+), and bacteria gram (-)) were separately added to soil at both sites. Substrate decomposition rates were substantially greater in LF than BF, as were overall respiration rates. After several months most new C was retained in the top 7.5cm at both sites, indicating insignificant loss due to leaching. While there were no significant differences in decomposition rates between temperate and tropical microbial additions at either site, there were treatment differences in C recovery within the microbial biomass C (MBC) pools, the dissolved organic C (DOC) pools, and recovery as CO2-C for both sites. Recovery as MBC at BF was initially greater for tropical additions than for temperate; at LF recovery as MBC was initially greater for temperate fungi and bacteria gram (+) than for tropical, and greater for tropical actinomycetes than for temperate. After several months, the trends at BF reversed, and there were little to no treatment effects at LF. Treatment recovery as DOC initially showed similar patterns to MBC-recovery at both sites, but after several months DOC-recovery drastically declined for all treatments, amounting to <0.05% of input C. Both soils respired more tropical fungi C than temperate, and more temperate actinomycetes C than tropical. These results demonstrate potentially different stabilization mechanisms associated with microbial groups and are most likely associated with differences in microbial biochemistry. The soil microbial community plays a key role in SOM dynamics, and this research provides important insight into these relationships and the biogeochemical processes governing soil carbon dynamics.
B23D-1584
Analysis and Modelling of Soil Carbon Dynamics and the Influence of Microbes in an Experimental Mesocosm Design
Soil is by far the largest carbon pool in terrestrial ecosystems, two to five times larger than total carbon in the current atmosphere, five times more than in living biomass on land. A lot of research has been done, but largely often concentrating on soil respiration as a overall measure of activity, but still little is known about soil carbon pool dynamics, and the influence of microbes. With the proposed experiment we want to quantify the relative usage of carbon from FOM (fresh organic matter) and/or SOM (soil organic matter) for microbes. Does microbial biomass change pool usage with varying conditions? How does temperature and moisture influence these pathways and how do they interact? A natural double label (13C, 14C) will be applied to mark carbon pools. The old C pool in the soil is labelled with a 14C signal and to follow the new C a 13C signal is used as marker (vegetation change). Two diurnal temperature treatments will be combined with two water treatments (constantly at field capacity and drying-rewetting respectively) to gain information on short direct effects of temperature (diurnal cycle) and longer-term effects (treatments). During the experiment the soil physical conditions and respiration rate will be continuously monitored. The amount and δ13C, δ14C values from phospholipid fatty acid (PLFA), added 13C labelled biomass, CO2, soil and soil solution will be used to quantify constitution of carbon from different. Experiment results will be further used for modelling pool behaviour to describe temporal and spatial C dynamics.
B23D-1585
The Distribution of Soil Organic Carbon Quantity and Quality in Soils of Southeastern Kentucky with Different Anthropogenic Histories
A better understanding of the distribution of soil organic carbon across the landscape is needed for inputs to regional and global carbon budget modeling. In this field-based research we collected soil samples from southeastern Kentucky to better understand the influence of land-use, land management history, anthropogenic disturbances and geomorphologic landform upon the carbon quantity, or total soil carbon, and quality, i.e., decomposition state, turnover and history. Choice of the study site focused on comparison of soil organic trends globally as well as regionally due to increased focus on coal production thus impacting soil carbon, the geomorphologic footprint of the downcut, dissected terrain, and the predominant land-use transition from forest to reclaimed grassland and agricultural. Soil samples were collected from deciduous and mixed forests, floodplains, agricultural, reclaimed grassland and reclaimed forest. Soil sampling included homogenizing samples from ten soil pits at each site at four different depth increments, separation of samples into soil organic carbon pools based on size class and density fractionation, and analyzing the samples using an isotope ratio mass spectrometer and total elemental analyzer. Analysis of our work and other published data in the temperate forests of Appalachia show little variability of carbon isotopic records with depth across the region which contrasts published results from tropical regions and suggests larger regional variability in soil carbon turnover rates for tropical rain forests than temperate forests. At the same time variability of surface soils in the temperate region due to recent anthropogenic and geomorphologic disturbance was pronounced for both soil carbon quantity and quality including: (1) Reclaimed forest and grassland surface soils in general showed lower total carbon in comparison to undisturbed forest surface soils, as expected. (2) Carbon to nitrogen atomic ratio and carbon and nitrogen isotopic signatures were similar for all forested surface soils, including reclaimed forests, mixed forest (slope and ridgetop), deciduous forest (slope and ridgetop) and deciduous floodplain soil, suggesting similar soil organic matter forming processes. (3) Floodplain forest soils showed significantly lower amounts of total carbon storage overall as compared to upland forest soils which was attributed to intermittent flooding and deposition of coarse, carbon poor sediments. This aspect was not reflected in traditionally used proxies but rather carbon and nitrogen isotopic signatures among carbon pools better explained flooding history and the mechanism of sediment transport during flooding. (4) The reclaimed grassland soil showed signs of lignite based on isotopic data. An un-mixing analysis is preliminary at this time but a method is being developed to isolate the contribution of soil organic carbon, which will be verified with petrography laboratory analysis. (5) Carbon and nitrogen isotopic values of the agricultural soils in hay conservation were in agreement with conservation soils in other parts of the United States, which reflects a transition from an anthropogenically controlled to more naturally controlled state.
B23D-1586
Soil C Quantification and CO2 Efflux in the Boreal Forest, James Bay, Canada.
The Boreal forest contains about 50% of the total organic carbon stored in forest ecosystems, and in these forests, the largest reservoir is the soil, because low temperatures promote net accumulation of organic C (Dioumaeva et al. 2003) These types of forest covers nearly 3 million km2, consequently, it can significantly influence the global carbon cycle (Kurz et al. 2002). Forest ecosystems take up atmospheric CO2 by converting into organic C through photosynthesis. Various physico-chemical and microbial properties of boreal forest soils regulating soil organic C (SOC) accumulation and decomposition are poorly understood. In this study, we present data on the quantity and quality of SOC in five different boreal forest types in the northern Quebec. The aims of our research are to (1) determine the role of several site-specfic variables influencing carbon storage such as forest stand composition, age, litter quality and production rate, as well as soil properties such as chemistry, drainage and texture, and (2) determine labile vs recalcitrant fractions of the SOC carbon as well as reactivity to temperature as related to the site characteristics described above. Results showed that litterfall, soil drainage class, and clay contents correlate significantly with the SOC contents in different forest types. Forest stand age and litter fall have a bearing on SOC accumulation rates. Forest type does not seem to affect SOC accumulation. Moreover, results suggest that drainage is a main driver of SOC accumulation. This project is still underway and we are currently measuring SOC mineralization rates under variable soil temperature regimes (2, 14 and 29 oC) in vitro to determine site specific difference in SOC quality and reactivity to temperature across forest stand types.
B23D-1587
Stable Carbon and Oxygen Isotope Composition of Soil and Shell from an Archeological Site in Kimble County, Texas
We report stable carbon (δ13C) and oxygen (δ18O) isotopic composition of inorganic carbonates, soil organic matter (SOM), and terrestrial gastropod shells present in a 130cm soil profile (radiocarbon date of 2340-2120 B.P) recovered from archeological site 41KM69, Kimble County, Texas. Prior to soil carbonate and SOM analyses, samples were treated with 5% sodium hypochlorite to remove organic matter and treated with 4% HCl to remove inorganic carbonate, respectively. Isotopic compositions of samples were obtained utilizing a Gasbench II (for carbonate-acid reaction technique) and a CHNS Elemental Analyzer (for SOM) coupled with a DeltaPlus XP Isotope Ratio Mass Spectrometer in continuous-flow. δ13C of carbonates in the soil profile varies in the range -2.15 to -4.63 ‰. δ18O of carbonates (ranging from -3.22 to -3.92‰) show little variation within the profile. δ13C of SOM (-25.61‰ to -22.83‰) suggests that C3 plants were predominant in the study area. There is ~3‰ enrichment in 13C of SOM at the bottom of profile relative to the top. Previous studies have shown that δ13C of modern soil carbonates are higher by 14-16‰ than SOM, whereas our results show about 20‰ difference. δ13C of land snail shells ( Rabdotus, Polygyra, Helicina) recovered from the soil show strong linear correlation with depth (R2= 0.88): -9.46‰ at 60cm to -5.4‰ at 112cm. δ18O of shells show no correlation with depth and range from - 3.34‰ to 0.62‰. Excluding one shell analysis, δ13C of shells and SOM exhibit good correlation (R2= 0.80). Previous studies of variation in δ13C in land snail shell document that carbon isotopic composition in shell are primarily a function of snail diet. Balakrishnan et al. (2005) have shown that δ13C of shells in C3 vegetation regimes range from -10.0‰ to -8.8‰, which is consistent with our results. Although, the interpretation of δ18O values in land snails is not straightforward, values are probably related to several different climate signals including temperature, rainfall, and relative humidity and may be used for potential markers of local climate conditions.
B23D-1588
Natural Terrestrial Sequestration Potential of Highplains Prairie to Subalpine Forest and Mined-Lands Soils Derived from Weathering of Tertiary Volcanics
There is now widespread agreement that, if the climate is to be stabilized, then net greenhouse gas emissions must be greatly reduced (IPCC, 2007). The need to reduce net CO2 emissions plus the possible economic and environmental ramifications of not addressing climate change have stimulated important atmospheric carbon mitigation actions, as well as, studies to understand and quantify potential carbon sinks. Soils represent a potentially large and environmentally significant natural carbon reservoir. Increasing the natural terrestrial sequestration potential (NTS) of soils is among the seven, "Sokolow CO2 stabilization wedges' or carbon management strategies needed to thwart doubling of atmospheric CO2. Additionally, high plains to subalpine temperate soils tend to be less susceptible to baseline C pool declines due to global warming than are warmer regions and are important ecosystems in which to quantify soil carbon storage capacity. To examine the potential of magnesium silicate-bearing soils to sequester additional carbon, we sampled 60 high plains prairie to subalpine forest soil horizons derived from weathering of Tertiary-age dacite-andesite- basalt compositions in Colorado, U.S.A.: the San Luis Valley, San Juan Volcanic Field, Grand Mesa, White River- Roan Plateau (Flat Tops), Rocky Mountain National Park, Front Range and propylitically-altered terrain in the western San Juan Volcanic field containing secondary magnesium silicates (chlorite-species). Data for C, N, O (total conc., isotopes), metals, major and trace elements, Hg, S, microbial enzymes (β-glucosidase, arylsulfatase, acid neutralizing capacity (ANC), and 14C radiocarbon dates are reported. Samples demonstrate variable but elevated C relative to average global soil C. In particular, the propylitically-altered rocks have a high instantaneous ANC in laboratory tests (> 20 kg/ton CaCO3 equivalent) and derivative forest soils containing low-temperature charcoal "burn" horizons have high total organic carbon contents (12-14 Wt.% in the A-B horizons; 0 to 30 cm). These data are important to understanding the carbon sequestration potential that soils derived from intermediate to mafic igneous rocks can provide. Additionally, for range or forest management and mine waste remediation scenarios, this data suggests C mitigation efforts may be augmented by ‘geomimicry' scenarios whereby projects model and enhance natural processes that support CO2 sequestration.
B23D-1589
Aliphatic and aromatic plant biopolymer dynamics in soil particles isolated from sequential density fractionation
A recent multi-layer-based soil organic matter-mineral interaction mechanistic model to describe the nature of soil organic matter-mineral surface mechanism for soil organic matter stabilization predicts that proteinaceous and aliphatic materials establish the core of strong binding-interactions upon which other organic matter is layered. A key methodology providing data underpinning this hypothesis is sequential density fractionation where soil is partitioned into particles of increasing density with the assumption that a partial control on organic matter distribution through density series is the thickness of its layering. Four soils of varying mineralogy and texture were investigated for their biopolymer, isotopic, and mineralogical properties. Light fractions (<1.8 g/cm3), although dominanted by organic detritus, did not always contain the highest concentration of lignin and substituted fatty acids from cutin and suberin while heavier fractions, 1.8-2.6 g/cm3, exhibited a progressive decrease in concentration in plant derived biopolymers with density. Extractable lignin phenols exhibited a progressive oxidation state with density. The concentration of biopolymers roughly mirrored the C:N ratio of soil particles which dropped consistently with increasing particle density. Although, in all soils, both lignin phenols and SFA concentration generally decreased with increasing density the ratio SFA/lignin varied with density and depending upon the soil. All soils, except the oxisol, exhibited an increase in SFA with respect to lignin suggesting a selective stabilization of those material with respect to lignin. In the oxisol, which showed little variation in its hematite dominated mineralogy across density, SFA/lignin remained constant, potentially indicating a greater capacity to stabilize lignin in that system. Interestingly, the lignin oxidation state increased with density in the oxisol. Given the variation in soil character, the consistency in these trends it suggests a general phenomenon of progressive decay in plant derived material with thinness of mineral coating but an overall relative increase in aliphatic character-all consistent with the multi-layer model.
B23D-1590
Evolution of Plant Biopolymer Chemistry of Above and Below Ground Input in a ýThorn Woodland Chronosequence
Encroachment of thorn woodlands into the grasslands of South Texas over the last 150-ýý200 years has resulted in greater above- and belowground biomass as well as greater ýoverall soil organic carbon (SOC) stocks. With the advancing age of woody clusters ýfrom initial mesquite occupation a variety of shrub and tree species become established in ýthe under story and often overtake the initial mesquite. This shift within clusters has ýimplications for the mass as well as chemistry of both above ground and below ground ýplant input to soils. Because this ecosystem shift results in an increased apportionment of ýcarbon to non aggregated, fast cycling SOC, the shifting biopolymer chemistry of plant ýinput may dramatically impact the microbial recalcitrance and residence time of SOC. ýWe document the specific plant contributors to a chronosequence (~90 years) of woody ýcluster encroachment and relate this to measured changes in litter chemistry, overall leaf ýand woody tissue input, and projected shifts in the chemistry to the soil as a result. ý
B23D-1591
Soil Biogeochemistry in the Ent DGVM
As the global climate continues to warm in the 21st century, it will be vital to assess the degree of carbon cycle feedbacks from the terrestrial biosphere, particularly the soil. Global soil carbon stocks, which amount to approximately double the carbon stored in vegetation, could provide either positive or negative climate feedbacks, depending on a given ecosystem's response to warming. To predict changes in net terrestrial CO2 fluxes and belowground organic carbon storage, we have developed and evaluated a soil biogeochemistry submodel for the Ent dynamic global vegetation model currently being tested within the GISS GCM. It is a modified version of the soil submodel in the CASA biosphere model (Potter et al., Glob. Biogeoch. Cyc. 7, 1993). We have enhanced it to allow for explicit depth structure (2 soil layers, 0-30 cm and 30-100 cm), first-order inter-layer (vertical) soil organic carbon transport, and a variable-Q10 temperature dependence for soil microbial respiration. We have tested the soil model in numerous offline runs. To spin up the simulated carbon pools offline, we conducted multi-century runs using meteorological and ecological data from various FLUXNET field sites that represent 7 of the 8 GISS GCM plant functional types: tundra, grassland, shrubland, savanna, deciduous forest, evergreen needleleaf forest, and tropical rainforest (the eighth, cropland, will be dealt with in a separate study). We then compare the magnitudes of the simulated spun-up soil pools to soil carbon stock data from these field sites as well as the biome-aggregated data from Post et al. (Nature 317, 1985). Net ecosystem CO2 fluxes and soil respiration are also compared to site-specific measurements where available. Preliminary results suggest that simulated fluxes are reasonably close to measured values, but simulated carbon storage tends to be lower than the measurements. In addition to site-specific comparisons, we discuss the broader implications of our results, e.g., the effects of including explicit depth structure and inter-layer soil carbon transport on simulated soil respiration, carbon storage, and estimation of the global carbon budget.
B23D-1592
Effects of Soil Water on Soil Surface CO2 Fluxes and the Carbon Budget of a Deciduous Forest
The CO2 flux from the soil surface is an important component of the carbon budget in a forest stand. The soil surface CO2 may contribute about 20 percent of the photosynthesis uptake by the forest with the remainder coming from the atmosphere. Since such a large fraction of the total CO2 flux above the forest canopy may originate in the soil, the contribution of soil surface CO2 flux must therefore be considered in using field measurements of CO2 fluxes to evaluate models for predicting the components of photosynthesis. The CO2 flux at the floor of a deciduous forest seems to depend on soil temperature, soil water content, amount of litter, and the photosynthesis capacity of the forest. An important way to understand these factors is to use fast response and accurate instrument to measure soil CO2 fluxes. We used a prototype soil chamber to measure soil CO2 fluxes at two locations in an oak forest in the NOAA-ATDD GEWEX flux tower network in TN, and the results from the measurement were used to evaluate the performance of a soil-plant-atmosphere model important as a gap- filling tool. Soil surface CO2 flux is the result of largely respiration by the soil biomass consisting of plant roots and dead plant materials. The respiration in vegetation environments depends on the capacity and types of vegetation, as well as on the mineralization of the organic matter by soil microbial activity, which provides nutrients for plant growth and development. In our case of the deciduous forest with large litter cover at floor below the canopy, CO2 flux may be produced by chemical reaction between rainwater and the top organic soil layer. During and immediately after rainfall, the CO2 dissolved in rainwater seems to be released from the warm soil relative to the rainwater. Similarly, CO2 may be released from the soil when rainwater displaces gas in the soil pore space. This physical interaction was observed at two flux tower sites in the oak forest reservation in Oak Ridge, TN. The soil chamber measurements reported strong increases in the hourly soil CO2 flux from low values of below 0.1 mg m-2 s-1 for dry soil conditions to values as high as 0.4 mg m-2 s-1 following rainstorm, suggesting that the soil CO2 flux is sensitive to soil water content. The fraction of the CO2 flux in the deciduous forest attributable to respiration seems to vary from 20 to 80 percent related to time of day and year and rainfall.
B23D-1593
The Origin of DIRT (Detrital Input and Removal Treatments): the Legacy of Dr. Francis D. Hole
Soil organic matter (SOM) plays a key role in the cycling and retention of nitrogen and carbon within soil. Both above and belowground detrital inputs determine the nature and quantity of SOM. Studies on detrital impacts on SOM dynamics are underway at several LTER, ILTER and LTER-affiliated sites using a common experimental design, Detrital Input and Removal Treatments (DIRT). The concept for DIRT was originally based on experimental plots established at the University of Wisconsin Arboretum by Dr. Francis D. Hole in 1956 to study the effects of detrital inputs on pedogenesis. These plots are located on two forested sites and two prairie sites within the arboretum. Manipulations of the forested sites include double litter, no litter and removal of the O and A horizons. Manipulations of the prairie sites include harvest, mulch, bare and burn. These original treatments have largely been maintained since 1956. After 40 years of maintenance, there were significant differences in soil carbon between the double and no litter plots. The double litter plots had increased by nearly 30% while the no litter plots had decreased over 50%. The original DIRT plots are now 50 years old and have been re-sampled, where possible, for total carbon and nitrogen, labile and recalcitrant carbon fractions, net and gross nitrogen mineralization rates, and SOM bioavailability through CO2 respiration. The soils were fractionated by density to examine the role of carbon in each density fraction. The mean age of carbon in each fraction was determined by radiocarbon dating. This sampling and analysis is of special significance because it provides a glimpse into the future SOM trajectories for the new DIRT sites: Harvard Forest (MA), Bousson (PA), Andrews Experimental Forest (OR) and Sikfokut (Hungary).
B23D-1594
Dissolved Organic Matter as a Mechanism for Carbon Stabilization at Depth in Wet Tropical Forest Volcanic Soils
Dissolved organic matter (DOM) plays an important role in many biological and chemical processes in soils. Our understanding of the types of plant and microbially-derived organic matter that accumulate in soils and the mechanisms responsible for their transformation and stabilization is still limited. In particular, we know very little about how microbial activity and water movement contribute to the production of DOM and the formation of stable C in soils. In well-drained soils under wet climates, DOM is potentially a primary pathway for the transport of C from the surface litter layers and the zones of highest microbial activity to deeper horizons in the soil profile where the potential for long-term storage increases. The mechanisms for long-term stabilization of organic C in deep mineral horizons include an accumulation of chemically recalcitrant C, strong sorption of soluble and otherwise labile C to mineral and/or metals making them inaccessible to decomposers, and microenvironmental conditions (low pH, low O2) which result in incomplete decomposition and persistence of labile C. Although most work to date has focused on the role of dissolved organic C and N (DOC and DON) in the C and N cycles of temperate forests, DOM fluxes may be even more important in forests in the wet tropics, where high rainfall and high primary productivity could lead to greater DOM production. In order to address the role of DOC in the transport and stabilization of C in mineral horizons, we are studying DOC production, transformation, and loss pathways in volcanic soils dominated by highly reactive, non-crystalline minerals (allophane). We are quantifying flux and solute concentrations (C, N, cations, anions) in rainwater, throughfall, and in soil water. We have installed tension and zero tension lysimeters throughout sequentially deeper organic and mineral horizons in an intermediate aged soil (ca. 350k years) under wet (ca. 3000 mm mean annual rainfall) native tropical forest cover on the island of Hawai'i. Previous research has measured soil organic C with very long mean residence times in the deeper mineral horizons at similar sites. Our study is focused on identifying the source of this highly stabilized C and the role of preferential water flow-paths in the vertical transport of C and nutrients. The soil's strongly blocky structure facilitates the downward movement of DOM to lower horizons where it comes in contact with allophane and is potentially sorbed. Through field sampling and laboratory manipulations, we will identify the zones of greatest DOC production and removal. Using separation by column chromatography (XAD resins), specific UV-absorbance, 13C-NMR, and microbial bioavailability assays, we will describe differences in the chemical composition of the organic material in solution amd solid-phase with depth.
B23D-1595
Plant and Microbial Controls on Soil Respiration in a Western Forest
We are using a combination of method to quantify controls on plant and microbial sources of soil respiration over the course of a year at the San Jacinto Mountains James Reserve in Southern California. High frequency autochamber flux measurements are combined with monitoring of air and soil temperature and moisture conditions to monitor diel and seasonal variations in flux. A total of eight autochambers are deployed in this seasonally dry, montane (2370 m) chaparral/mixed hardwood and conifer forest. Partitioning between autotrophic and heterotrophic sources is accomplished by trenching (in April 2007) around four of the chambers to a depth of 60 cm to remove the autotrophic component, and a mass balance approach using radiocarbon measurements of respired CO2 and its root and microbial sources. The climate at this site is characterized by a winter wet season and a long (April-November) dry season, punctuated by occasional summer thunderstorm activity. When soil and surface litter are moist in the wet season, temperature (2cm) is the major correlate for soil respiration. Isotope mass balance partitioning in March shows that 37 +/- 16 per cent of the total respiration is from sources with the radiocarbon signature of root respiration. As the ecosystem enters the dry season, soil respiration fluxes decline to low levels, the amplitude of the diel cycle decreases. Fluxes in this period are anti- correlated with temperature and more closely follow fluctuations in air relative humidity and litter moisture. By July, there was little difference in either soil respiration fluxes or the isotopic signature of respired CO2 between the trenched and untrenched plots, suggesting that less than 12 per cent of the respired CO2 is from root respiration sources. We will update these data to include the effects of anticipated summer moisture events. Overall the combination of frequent measurements of soil respiration with isotopic and experimental manipulation provides a framework for developing models that separate effects of temperature, moisture and season on autotrophic and heterotrophic respiration sources.
B23D-1596
Small Degree of Trace Element Enrichment in Soils not Surprising, in View of Measured Deposition by Dusts
Atmospheric dust deposited onto the surface of the land is enriched in trace elements (e.g., Zn, Cu, Pb, Cd, others). That is, trace elements in the dust have greater abundances than can be accounted for by the expected amounts in the crystals of the minerals of which the dust is composed. This has been true since pre-industrial times. Substantial excess masses of trace elements are currently deposited to the land surface in the U.S. Southwest (e.g., in ug/m2/yr: Cu, 160; Zn, 500; As, 15; Sb, 5; Pb, 60; Bi, 2). If these annual excess masses were newly arriving from some distant source and accumulating in the local soils, times on the order of 50Ky would be required to double the trace element concentrations in a 10 cm thickness of surficial material (soil) of crustal composition. But much of the trace element mass coming with dust is recycled, through both local and distant soils, and some is exported (to oceans) during recycling. Therefore times required for doubling of concentrations are longer, and any trace element enrichments in soils (elevations of concentration above crustal levels) must have begun to accumulate long before modern industrial times. It is therefore not surprising that the few available data on trace elements in soils show that enrichments are small ("enrichment factors" in non-quartz fraction of some Utah soils (Goldstein et al, 2005) are: As, 6; Pb, 3; Sb, 6, Tl, 1.2; Zn, 1.6; Cd, 1.6, Cu. 1.5). Several natural sources of supply of excess of trace elements to the atmospheric dusts (and hence to soils) have been proposed: volcano emissions, plants, sea surface slimes, preferential weathering of rocks. But only the volcanic source has been documented and quantified (Hinkley et al., 1999; Matsumoto and Hinkley, 2001). We note that the present rate of apparent excess deposition in the Southwest is about 10-100 times the present rate of worldwide emission to the atmosphere through degassing by volcanoes. Considering the long times available for accumulation, and that modern measured deposition is recycled through the soil reservoir and the atmosphere, the volcanic source may have sufficient strength to be a main ultimate source of the trace element enrichment observed in atmospheric dust.
B23D-1597
Abiotic Immobilization of Nitrate in Forest Soils: a Double Label Approach
Mechanisms of soil nitrogen (N) retention remain a key uncertainty in the terrestrial N cycle. During recent work at the Harvard Forest Chronic N Experiment, 15N added to soils as ammonia nitrate was observed to be rapidly immobilized after addition to soil on a time scale of minutes. In published results it was hypothesized that the rapid time of immobilization could be explained by abiotic immobilization of both ammonia and nitrate. The possibility of abiotic immobilization of nitrate has been studied since the first half of the 20th century, mainly using ideal compounds and soil sterilization techniques. However, critics of these studies have argued that while in vitro studies may indicate the possibility of an abiotic reaction, they cannot demonstrate its plausibility in soils. Soil sterilization methods have been criticized, because they are not effective enough to eliminate biotic interactions within an experimental treatment. Isotopic tracer studies have also been used but also have problems differentiating biotic and abiotic reactions. This study is an attempt to demonstrate abiotic immobilization of nitrate in soil samples through the use of double labeled nitrate (15N18O3- ). The resolution of this method depends on the biochemistry of microbial immobilization of nitrate; reduction of nitrate to nitrite, then ammonia and glutamine before incorporation into microbial biomass. Reduction of 15N18O3- before microbial utilization of the 15N implies that retention of both heavy isotopes in the soil can only occur through abiotic reaction of 15N18Ox species. In biotic immobilization the 18O is lost to the system in water. While nitrate has proven unreactive in soils, its reduced product, nitrite, is known to be readily reactive with various soil compounds. Nitrite can be introduced into the soil environment naturally by both ‘leakiness' in nitrification and denitrification and may possibly be generated abiotically through methods such as the proposed Ferrous Wheel hypothesis. Samples of the O-horizon of Harvard Forest red pine soils were incubated at several short intervals (15 m, 1 h, 4 h), based on previous observations made at Harvard Forest, under both anoxic and oxygenated conditions. Following incubation, KCl extraction of available N, and freeze drying, isotopic enrichment was determined by EA/TCEA Mass Spectroscopy. Preliminary results showed a significant enrichment in 15N and a small but significant enrichment in 18O. The full results of the experiment will be available by the Fall meeting.
B23D-1598
Spatial Variability of the Stocks of Different Organic Carbon Fractions in a Leptic Cambisol under Norway Spruce
Soil organic carbon (OC) stocks of forest soils are known to be characterized by large small scale variability. The variability of different OC fractions (HF-soluble OC fraction, representing mineral associated OC; HF-resistant OC fraction, representing the non-mineral associated OC) is largely unknown. The same is true for their relation to site specific factors (e.g. bulk density, pH, content of oxalate extractable iron and aluminum oxides). We studied a dystric, laxic Leptic Cambisol site (0.09 ha) stocked with Norway spruce in the Nationalpark Bayerischer Wald, Germany. Soil samples from the Ah and the Bw1 horizon were taken at the knots of a rectangular grid with distances of 5 m. Small scale variability was determined using a nested sampling scheme with a minimum horizontal sampling distance of 0.2 m. Mineral associated and non-mineral associated OC stocks in the soil were characterized by ordinary statistics and geostatistics. In order to examine spatial relations between OC stocks and site specific factors, experimental crossvariograms were calculated. Additionally, we compared the spatial variability of different OC species of the HF-soluble and non-soluble fraction as determined by 13C CPMAS NMR spectroscopy with and without prior HF-treatment. Comparison of the HF-soluble and the non-soluble OC stocks showed that only the HF-soluble OC stock exhibited a spatial pattern. In contrast, the non-soluble OC stocks were characterized by a pure nugget effect. HF- soluble OC stocks were significantly negatively spatially correlated with the pH, but positively correlated with the amount of oxalate extractable iron and aluminum oxides in both horizons. In contrast, bulk density showed a significant spatial correlation with the HF-soluble OC stock only in the subsoil. Comparison of the spatial variability of different HF-soluble OC species showed an increasing spatial variability in the order aryl C < carboxyl C < alkyl C < O/N-alkyl C. Our results indicate that the spatial variability of OC stocks is mainly due to the spatial variability of the HF-soluble, i.e. mineral-associated OC. HF-soluble OC stocks consequently increase with increasing amounts of oxalate extractable iron and aluminum oxides and with decreasing pH. This is due to an increasing sorption capacity of these oxides at lower pH. Different spatial distribution patterns of different OC species indicate specific stabilization mechanisms for the respective species.
B23D-1599
Tannin-Metal Interactions in Soils: An Incubation-Extraction Approach in Hill-Land Environments
Tannins, plant polyphenols known to react with proteins, metals and soil organic matter, are commonly found in the vegetation growing in Appalachian hill-lands. Establishing silvopastoral grazing systems in these environments is a means for improving productivity however the fate of tannins in soils and, in particular, the effect on solubility/mobility of metals in soils is poorly understood. Soils from forest and pasture systems were sampled from two depths, treated with tannic acid or related phenolic compounds, and analyzed for metals in solution. The amount of Mn and Ca detected in solution varied among the different phenolic treatments, highest for gallic acid, and was also influenced by depth and land use. As expected, the Ca content in solution was correlated with the electrical conductivity (EC) and the Mn content was correlated with the redox potential in solution. Interestingly, the EC was also correlated with both Mn content and redox potential. The higher Ca content found in solution may result from the low pH of the phenolic compounds. The higher Mn in solution may result from the redox reaction of Mn (IV) oxides with the phenolic compounds, producing soluble Mn2+ and quinones. These quinones are very reactive compounds that can self-polymerize and/or copolymerize with other biomolecules, such as amino-containing compounds and carbohydrates, to form humic-like substances. Successful management of silvopastures, requires an understanding of factors that affect the quality and quantity of plant secondary compounds like tannins entering soil not only to increase forage productivity but also to enhance formation/stabilization of soil organic matter to increase nutrient cycling and reduce the toxicity risk of some metals such as Mn.
B23D-1600
Nano-Scale Secondary Ion Mass Spectrometry: Potential And Pitfalls Of This Technique For Soil Organic Matter Stabilization
The mechanisms by which organic matter is stabilized in soils are still poorly understood, and it is notable that some postulated mechanisms are currently only weakly supported by data. A major obstacle to progress is the lack of techniques of adequate sensitivity and resolution for data collection needed to further our understanding of soil organic matter stabilization at relevant scales. Nano-Secondary Ion Mass Spectrometry (NanoSIMS) is a cutting edge technology linking high resolution microscopy with isotopic analysis, which allows precise, spatially-explicit, elemental and isotopic analysis at micro-and nanoscale. The power of NanoSIMS lies in the ability of the instrument to distinguish stable isotopes of elements with a high sensitivity, i.e. concentrations in parts per million can be detected. The level of spatial resolution achievable is better than 50 nm (133Cs+ primary beam) with NanoSIMS, a significant improvement on other SIMS instruments and on X-ray micro-analytical techniques. These instruments have been applied to studies of presolar materials from meteorites, in material science, geology and mineralogy as well as biology. Recently, the potential of NanoSIMS has been demonstrated to explore in situ the biophysical interface in soils (Herrmann et al., 2007). I will present recent findings illustrating the capacity of NanoSIMS to improve our fundamental understanding of soil processes at the nano- and micro-scale, along with my experiences in the methodological approaches that need consideration with respect to experimental design and sample preparation. Herrmann, AM, Clode, PL, Fletcher, IR, Nunan N, Stockdale, EA, O'Donnell, AG, Murphy, DV, 2007. A novel method for the study of the biophysical interface in soils using nano-scale secondary ion mass spectrometry. Rapid Communications in Mass Spectrometry 21, 29-34.
B23D-1601
Landscape Controls of CH4 Fluxes in a Catchment of the Forest Tundra in Northern Siberia
Soils have the capacity to both produce and consume atmospheric methane. The direction and the size of net- CH4 exchange between soils and atmosphere is mainly controlled by the soil aeration, temperature and the amount of bioavailable organic matter. All these factors are strongly influenced by distribution and seasonal dynamics of permafrost. Thus, distribution of permafrost and the thickness of the active layer can exert strong influence on CH4 dynamics in artic and northern boreal ecosystems. We analyzed the spatial and temporal variability of net-CH4 exchange within a catchment located in the Siberian forest tundra at the eastern shore of the lower Yenissej River to constrain the current function of this region as a sink or source of atmospheric CH4 and to gain insight into the potential for climatic change to alter the rate and form of carbon cycling and CH4 fluxes in this region. Net-fluxes of CH4 were measured from July to November 2003 and from August 2006 to July 2007 on representative soils of the catchment (mineral soils with different thawing depth, soils of bog plateaux) and on a thermokarst pond. In addition, dissolved CH4 in the stream draining the catchment was determined. Field observations, classification of landscape structures from satellite images and flux measurements were combined to estimate total catchment CH4 exchange. Nearly all soils of the catchment were net-sinks of atmospheric CH4 with annual CH4-C uptake rates ranging between 1.2 and 0.2 kg ha-1 yr-1. The active layer depth was the main factor determining the size of CH4 uptake. Total net-exchange of CH4 from the catchment was dominated by ponds that covered only about 2% of the catchment area. Due to high CH4 emission from these aquatic systems, the catchment was a net source of atmospheric CH4 with a mean annual emission of approximately 170 kg CH4-C ha-1. CH4 concentration in streams draining the catchment can help to identify areas with high CH4 production. The results suggest that CH4 emission in this region is strongly influenced by permafrost degradation and thermokarst erosion in bog areas.
B23D-1602
Spatial Variation in Carbon Release From Arctic Tundra Resulting From Microtopography Created by Permafrost Thawing
One of the biggest potential feedbacks to global climate change from high latitude ecosystems may come from thawing of permafrost, which stores 30% of the total global terrestrial soil organic carbon (SOC). Thawing of permafrost may accelerate decomposition of soil organic matter (SOM) and increase carbon dioxide (CO2) emissions and such emissions from soil can lead to further warming in global scale. When permafrost thaws in ice-rich areas, it creates localized topographical surface subsidence called thermokarst, which can induce variations in soil abiotic properties. By altering multiple resources in soil, thermokarst can change C cycling in high latitude ecosystems beyond simple increases in temperature alone. The objective was to determine how thermokarst affects ecosystem C exchange. We hypothesized that there would be a positive relationship between the degree of ground subsidence and CO2 emissions from decomposition of SOM. This study was conducted in a tundra site near Denali National Park, Alaska. Three study sites were established according to the degree of surface depressions: Severe Thaw, Moderate Thaw, and Minimal Thaw. We established 50 equally spaced grid points each site and they were surveyed using GPS to measure the micro-elevation. Clear static chamber measurements were used to measure ecosystem C exchange, while soil properties such as temperature and volumetric water content (VWC) were measured simultaneously. Normalized Difference Vegetation Index (NDVI) was measured as an indicator of primary productivity. We used forward stepwise regression analysis to quantify how much microtopography explained ecosystem C exchange. There was a negative correlation between ecosystem respiration and relative elevation at the Severe and Minimal site. The best predictor variable for ecosystem C exchange was VWC alone, which was better than temperature alone, or mixed effects of temperature and VWC. There was no relationship between NDVI and microtopography, which supports the idea that thermokarst alters soil processes more than primary productivity. Subsided areas showed high CO2 emissions; therefore, we suggest thermokarst development may play major role in stimulating CO2 emissions from high latitude ecosystems.
B23D-1603
The role of lakes in carbon transfers from permafrost to the atmosphere
In interior Alaska, permafrost thawing is increasing hydrologic losses of soil carbon. At the Eight Mile Lake watershed (outside Denali National Park), dissolved organic carbon (DOC) in soil lysimeters and surface runoff, ranged from 15 to 30 mg L-1 in areas with minimally thawed tussock tundra. In drainages with moderately and severely thawed permafrost, DOC concentrations ranged from 25 to 55 mg L-1. Dissolved CO2 concentrations in surface runoff and soil water ranged from 3 to 25 mg L-1 C-CO2 and increased with depth of the water table. As inflowing waters transited through Eight Mile Lake they re-equilibrated with respect to CO2 (lake water C-CO2 < 1 mg L-1) and DOC concentrations decreased by 10-20 mg L-1. On an areal basis, hydrologic yield of carbon (DOC+DIC) measured at the lake inlet was 5.6 g m-2, whereas at the outlet, yield decreased to 2.4 g m-2. Heterotrophic bioavailability of organic matter in the lake ranged from 9-14% over 28-day incubations. In contrast, short-term (2-7 day) exposures to ambient sunlight and mineral sediments resulted in losses of 16-22% of DOC in waters collected from inflow streams and soil lysimeters. These experiments indicate that abiotic processes may dominate as the carbon loss mechanism in Eight Mile Lake. Our results suggest that in-lake processing of DOC and DIC may strongly influence regional carbon balances in interior Alaska.
B23D-1604
Using radiocarbon to detect the loss of old soil carbon in hydrologic fluxes from permafrost
Transfers of C to the atmosphere from melting permafrost have been hypothesized to be a positive feedback to climate change. However, sustained and significant transfers must come from old C, which forms the bulk of the soil pool, and may be detectable in the Δ14C isotopic signature of hydrologic C losses. At the Eight Mile Lake watershed (Healy, Alaska) we have made regular measurements of the Δ14C of DOC and DIC in surface inflow to the lake and in waters draining a severely thawed tussock tundra subcatchment. Δ14C- DIC values typically ranged from +40 to +70 permil and suggest that the DIC pool at both locations is in near isotopic-equilibrium with the atmosphere. In surface inflow, Δ14C-DOC values ranged from +20 to +60 permil, while in drainage from severely thawed permafrost values ranged from -20 to +20 permil. At both sites, Δ14C-DOC was lowest at the onset of snowmelt in the spring (ca. April-May) and gradually increased until freezing occurred in September. Negative Δ14C-DOC values in waters draining thermokarst features demonstrate a substantial amount of older, temperature stablized carbon is mobilized in the spring when DOC concentrations are at maximum (40 to 50 mg L-1).
B23D-1605
Microbial decomposer communities in Alaskan permafrost soils and their response to thaw
Permafrost protected soil carbon in boreal forest ecosystems represents a significant portion of the approximately 500 Gt C in the soil organic matter of boreal regions. The magnitude of this thermally-protected carbon pool makes it a particularly important to the global C cycle within the context of global climatic change. Permafrost has acted as a C sink for thousands of years yet currently has been warming at a rate of 1°C per decade, making the C contained within it potentially available for decomposition. Thawing permafrost opens a latch into a globally important C reservoir that could be released to the atmosphere (as CO2) and rivers (as dissolved organic carbon, DOC), affecting greenhouse warming and aquatic chemistry. A gap in our current knowledge is the extent to which permafrost-protected C is available for microbial metabolism once soils thaw. Current indications are that organic matter contained within permafrost is relatively labile since it is not protected from decomposition by physical protection or humification mechanisms. However, we have little understanding of the microbiology of permafrost soils, which could significantly affect the rate of decomposition of permafrost C after thaw. Our aim was to use quantitative molecular techniques to examine the abundance of microbial decomposer functional groups in permafrost soils, the enzymes they encode, and their rates of respiration under both aerobic and anaerobic conditions in a simulated summer thaw at 5°C. We compared microbial and chemical characteristics of active layer and permafrost soils from black spruce stands in three distinct geographic regions: Coldfoot, Hess Creek, and Smith Lake, AK. We chose these regions because they span a range of permafrost conditions from shallow active layers and mineral-associated permafrost layers to thick active layers and deep organic permafrost soils. Soil carbon and nitrogen concentrations did not differ between active layer and permafrost soils within sites, and neither did the relative abundance of total bacteria and methanogens. In contrast, total fungal abundance and basidiomycete abundance was strongly reduced in permafrost soils. We tested whether the reduction in fungal abundance in permafrost soils could affect the turnover of soil carbon in thawed permafrost. We incubated soils under aerobic and anaerobic conditions at 5°C for 3 months. We are currently examining the changes in microbial respiration and enzyme activities that result from the incubation, as well as microbial population shifts. We are testing the hypothesis that low fungal biomass in permafrost soils will reduce the rate of decomposition of organic matter during summer thaw. http://carbon.wr.usgs.gov/
B23D-1606
Experimental thawing of permafrost changes carbon cycling attributes in tussock tundra in N. Alaska
Global warming is expected to be amplified in the arctic, causing increased permafrost thawing. However, few studies have experimentally addressed the consequences deeper active layers as permafrost melts. The consequences of thawed permafrost may be multifaceted, including deeper active layers, changes in vegetation rooting depth and alterations in the pools and magnitudes of carbon efflux to the atmosphere. After 13 years, a long-term snow addition experiment has doubled the active layer depth from ~30 to 60 cm, thawing permafrost in a portion of tussock tundra at Toolik Lake, AK. We used radiocarbon to partition respiration into autotrophic and heterotrophic components as well as gas probes to measure the C respired at depth under control and thawed permafrost conditions. Radiocarbon signatures of field respiration were higher in the snow fence plots (105‰, ±17) than in the control plots 69‰, ±12), reflecting higher 14C of heterotrophic respiration and/or decreased root respiration in the experimental plots (p =0.027, t-test). The soil gas probes near the maximum thaw depth in each treatment showed that the C respired had much lower 14C values in the snow drift plots compared to the control plots (-106‰, ±39 vs. 41‰, ±18, p=0.007, t-test). This corresponds to mean ages of approximately 1000 years old for the snow drift plots and less than 100 years for the controls.
B23D-1607
Dynamic vegetation enhances global warming and accelerates soil carbon decomposition
We used an atmospheric general circulation model (AGCM) coupled interactively to a dynamic global vegetation model (DGVM) in order to quantify the climate feedback caused by changes in the distribution of vegetation under quadrupled atmospheric CO2 concentration relative to preindustrial value. With the introduction of dynamic vegetation, global warming is amplified by approximately 10%, and total terrestrial carbon storage is reduced by 12%, primarily due to the amplification of warming caused by albedo feedback related to forest change at high latitudes (e.g., tundra to taiga) and accelerated soil carbon decomposition at northern middle and high latitudes. We also performed an additional experiment without the fertilization effect due to elevated atmospheric CO2. The result of this additional experiment indicates the vegetation change in arid and semi-arid regions in low latitudes also contributes the amplification of warming and acceleration of soil carbon decomposition.
B23D-1608
Warming-Induced Changes to the Molecular Composition of Soil Organic Matter
Soil organic matter (SOM) contains two times more carbon than the atmosphere and the potential changes to SOM quantity and quality with global warming are a major concern. It is commonly believed that global warming will accelerate the decomposition of labile SOM compounds while refractory SOM constituents will remain stable. However, experimental evidence of molecular-level changes to SOM composition with global warming is currently lacking. Here we employ SOM biomarkers and nuclear magnetic resonance (NMR) spectroscopy to study SOM composition and degradation in a soil warming experiment in southern Ontario, Canada. The soil warming experiment consisted of a control and a treatment plot in a mixed forest that had a temperature difference of about 5 degrees C for 14 months. Before soil warming the control and treatment plots had the same organic carbon (OC) content and SOM composition. Soil warming significantly increased soil OC content and the abundance of cutin-derived carbon originating from leaf tissues and decreased carbohydrates that are regarded as easily degradable. Lignin components, which are believed to be part of the stable and slowly-cycling SOM, were observed to be in an advanced stage of degradation. This observation is corroborated by increases in fungal biomass in the warmed soil because fungi are considered the primary decomposer of lignin in the soil environment. An NMR study of SOM in the warmed and control plots indicates that alkyl carbon, mainly originating from plant cuticles in the soil, increased in the warmed soil while O-alkyl carbon, primarily occurring in carbohydrates, decreased. Aromatic and phenolic carbon regions, which include the main structures found in lignin, decreased in the warmed soil. These data collectively suggest that there is a great potential for lignin degradation with soil warming, and that the refractory (aromatic) soil carbon storage may be reduced as a result of increased fungal growth in a warmer climate.
B23D-1609
Temperature Responses of Soil Organic Matter Components With Varying Recalcitrance
The response of soil organic matter (SOM) to global warming remains unclear partly due to the chemical heterogeneity of SOM composition. In this study, the decomposition of SOM from two grassland soils was investigated in a one-year laboratory incubation at six different temperatures. SOM was separated into solvent- extractable compounds, suberin- and cutin-derived compounds, and lignin monomers by solvent extraction, base hydrolysis, and CuO oxidation, respectively. These SOM components had distinct chemical structures and recalcitrance, and their decomposition was fitted by a two-pool exponential decay model. The stability of SOM components was assessed using geochemical parameters and kinetic parameters derived from model fitting. Lignin monomers exhibited much lower decay rates than solvent-extractable compounds and a relatively low percentage of lignin monomers partitioned into the labile SOM pool, which confirmed the generally accepted recalcitrance of lignin compounds. Suberin- and cutin-derived compounds had a poor fitting for the exponential decay model, and their recalcitrance was shown by the geochemical degradation parameter which stabilized during the incubation. The aliphatic components of suberin degraded faster than cutin-derived compounds, suggesting that cutin-derived compounds in the soil may be at a higher stage of degradation than suberin- derived compounds. The temperature sensitivity of decomposition, expressed as Q10, was derived from the relationship between temperature and SOM decay rates. SOM components exhibited varying temperature responses and the decomposition of the recalcitrant lignin monomers had much higher Q10 values than soil respiration or the solvent-extractable compounds decomposition. Our study shows that the decomposition of recalcitrant SOM is highly sensitive to temperature, more so than bulk soil mineralization. This observation suggests a potential acceleration in the degradation of the recalcitrant SOM pool with global warming.
B23D-1610
Influence of Soil Organic Matter Stabilization Mechanisms on Temperature Sensitivity of Soil Respiration
Knowledge on the sensitivity of soil organic matter (SOM) respiration to changes in temperature is crucial for predicting future impacts of climate change on soil C stocks. Temperature sensitivity of respiration is determined by the chemical structure of the compound to be decomposed and by the availability of the organic matter for decomposers. Biochemically recalcitrant SOM has a higher temperature sensitivity than biochemically labile SOM. However, it is hypothesized that the stabilization of SOM by interaction with the soil matrix could be an important attenuating control on temperature sensitivity. We investigated the effect of different SOM stabilization mechanisms on temperature sensitivity of SOM respiration. Two main mechanisms were considered: chemical interactions of SOM with clay and silt particles, and physical protection inside aggregates. Soil samples from an agricultural silt loam soil were fractionated by wet-sieving into macroaggregates, microaggregates and silt+clay fractions. SOM stabilization in the silt+clay fraction occurs mainly chemically, whereas in aggregates physical protection of SOM is more important. Samples of each fraction and of bulk soil were incubated at two temperatures (20°C and 30°C) for one month. After 2% of total soil carbon was respired, temperature sensitivity was determined for respiration of the next 0.5% of total soil carbon. This was done by calculating a Q10 value as the ratio of the times needed at each temperature to respire that fraction of the soil C. This method allows determination of temperature sensitivity independent of C quality. Calculated Q10 values decreased in the order bulk soil > macroaggregates > microaggregates > silt+clay, with the difference between macroaggregate Q10 and silt+clay Q10 being the only significant difference. These results indicate that protection of SOM attenuates temperature sensitivity, with chemical protection (silt+clay) having a larger effect than physical protection (aggregates).
B23D-1611
The Carbon Cycle in Karst Areas: Anomalies of Carbon Dioxide Concentrations in the Underground Atmosphere of Carburangeli Cave (Italy).
The Carburangeli Cave is a small underground environment, protected by a natural reserve, located within a limestone karst area, very close to the ground surface, in the surroundings of the city of Palermo, on the northern coast of Sicily (Italy). Between August 2006 and August 2007 hourly measures of external air temperature, rainfall amount, underground air temperature and static carbon dioxide concentrations and dropping waters amount have been carried out, together with monthly sampling and chemical analysis of underground waters circulating inside the cave. Chemical analyses showed very high concentrations of bicarbonates and calcium, highlighting a strong interactions between infiltrating waters, soil and bedrocks, despite the very shallow hydrologic circuit. Excess CO2 in infiltrating waters is released in the cave atmosphere, as testified by the very high concentrations (more than 2%) measured especially during periods characterized by the block of air circulation between the underground environment and the external atmosphere, on their own due to density differentials induced by the different thermal regimes. The simultaneous measurements of rainfall and dropping waters amounts allowed the evaluation of the infiltration response under different rainfall dynamics, highlighting how under elevated rain rate no significant infiltration takes place, despite the very high permeability typical of karst areas. The high concentrations of carbon species found in infiltrating waters, also in the very shallow circuit of Carburangeli Cave, evidence how karst areas play a very important role as a CO2 sink, although fixation of carbon dioxide could be less efficient under a scenario of more intense rainfalls and higher air temperatures.
B23D-1612
Changes of Soil Aggregate C Isotopes in No-Till Corn Following Bromegrass.
This field study is near Ithaca, Nebraska, USA (lat. 41.151, long. 96.401) on a Filbert silt loam (fine, smectitic, mesic Vertic Argialboll). The site was in bromegrass since 1986. Corn was no-till seeded into the bromegrass sod in spring 1999. A randomized complete block design with three replicates was used. No-till corn was the main treatment with nitrogen (N) as subplots. N was broadcast at the start of each growing season at 60 or 120 kg N/ha as NH4NO3. Total biomass was measured by weighing 4.4 m of row in each plot. Soil samples were obtained in May 1999 (baseline sampling), Sept 1999, June 2000, Oct 2000, Sept 2001, Nov 2002, Sept 2003, and Oct 2005 from pre-selected areas by removal of plant material from the soil surface and removing the 0-5, 5- 10, and at 4 of the 8 harvests also sampling the 10-30 cm depths with a flat-bladed shovel. Soil bulk densities were determined on clods from each layer. The moist soil was passed through an 8 mm sieve before air drying and storing. Aggregate size fractions were obtained with a Yoder wet-aggregate method. Soil size fractions obtained were > 2, 1, 0.5, 0.25, 0.125, 0.045 and < 0.045 mm. Detritus was floated to the surface and skimmed off for transfer to a separate container. Aggregates were dried at 55°C, weighed, ground, and analyzed for total C and N and 13C:12C isotope ratio. Because soil organic carbon (SOC) was labeled with the bromegrass (C3 plant) isotope signature, then during the 77 months of this experiment the re-labeling of each fraction and the total SOC with the corn (C4 plant) isotope signature and the amounts of SOC lost from aggregate size fractions with conversion of the bromegrass sod to no-till corn was measured. During 6.5 years, total SOC decreased from 21.1, 17.0, and 55.8 t/ha in the 0-5, 5-10, and 10-30 cm depths to 20.1, 16.7, and 55.5 t/ha, respectively. However the SOC in the < 2, 0.5–2, and < 0.5 mm fractions of the 0 – 5 cm depth changed from 62, 21, and 16 % of the total SOC at the studies beginning to 31, 40, and 29 %, respectively, by the end of 77 months. Weight of SOC from C4 plants was 34.8, 49.8, and 73.2 % of total SOC in the 0–5, 5–10, and 0–30 cm depths, respectively at the beginning of the study, but after 77 months of no-till corn was 47.3, 59.0, and 71.8 % of total SOC for these same depths. In summary, it is important to evaluate losses or gains of SOC under cultivation. Use of the 13C:12C ratios, as influenced by reversing the growing sequence of C3 vs. C4 plants, allows losses of older SOC from C3 plants (bromegrass) vs. that added by growing C4 plants (corn) to be determined over time and allows rates of change of the SOC associated with various soil fractions to be evaluated.
B23D-1613
Variation of Ecosystem Respiration with Different Vegetations at Different Microtopographies
Department of Biology, San Diego State University, San Diego, CA 92182, USA Abstract: Arctic tundra is one of the significant stocks of terrestrial soil carbon. With global climate change, it is likely that the distribution of vegetation types was altered at high latitudes. Consequently the ecosystem CO2 emission will be changed with the alteration. To predict the change trend due to global change in the future, it is critical to clarify the variation of CO2 emission from ecosystem to atmosphere at different topographies and vegetation types. In this study, we conducted 16 plots with three different vegetation types: Dry lichen, Sphagnum moss, Carex at five different micro topographies: low center polygon, high center polygon, rim, trough and flat at Barrow, Alaska. Automatic chamber system Licor-8100 and Licor-8150 were applied to observe ecosystem respiration continually from middle June 2007 to the end of August 2007. Soil temperature, soil moisture were measured at the same time. Thaw depth, water table and Normalized Difference Vegetation Index (NDVI) were observed at each plot with a frequency once a week. As a result, the flat area with Carex vegetation was significantly greater than other micro topographies with other vegetations. High center polygons have the lowest ecosystem respiration even with different vegetations. These results suggest that both micro topography and vegetation play key role on the variability of ecosystem CO2 emission. Middle-level water table, high thaw depth, and appropriate NDVI will increase the emission of CO2 from ecosystem to atmosphere. With the season changing, ecosystem respiration increased with higher temperature and lower water table and soil moisture. Key words: ecosystem respiration, microtopography, vegetation type
B23D-1614
Changes in Soil Carbon and Nitrogen in a Multi-factor Climate Change Experiment on Constructed Old-Fields
Single factor experiments indicate elevated CO2 concentrations increase soil C stocks, but relatively few experiments have examined the effects of interacting environmental factors on soil C dynamics. We undertook studies in a multi-factor (CO2 x temperature x moisture) experiment in east Tennessee to better understand the effects of these factors and their interactions on soil C and N in a constructed old-field community that included 7 species (including two N-fixers). Symbiotic N-fixation was an important process supplying N to Lespedeza cuneata, an invasive legume that dominated the communities after 3 years of treatments. Following four growing seasons, elevated CO2 had no measurable effect on C and N concentrations in whole soils, particulate organic matter (POM), and mineral-associated organic matter (MOM). There were no statistically significant interactions involving CO2 x temperature, CO2 x water, or CO2 x temperature x water. Soil moisture was the main factor affecting soil C and N following 4 years of treatments. Analysis of stable C isotopes indicated that the fraction of new C increased significantly in whole soils, POM, and MOM, and that the greatest gains (50% new C) were measured in POM under elevated soil moisture. Despite high rates of N- fixation and significant belowground inputs of new soil organic matter, soil C and N concentrations and C stocks in POM declined significantly over 4 years under conditions of higher soil moisture. Higher soil moisture increased soil respiration and calculated turnover times indicated overall faster soil C cycling under elevated soil moisture in the elevated CO2 treatment plots. Higher soil moisture accelerated heterotrophic decomposition of labile soil organic matter more than it increased soil C inputs under elevated CO2. The imbalance produced a net decline in soil C stocks and a widening of soil C/N ratios. POM was the most sensitive pool for detecting rapid changes in soil C in response to environmental change. Rapid loss of POM C, and associated declines in soil quality, would tend to promote long-term changes in plant community composition by favoring invasive N-fixers, like Lespedeza cuneata.