B41C-0638 

A novel approach to inferring real temperature sensitivity and soil carbon dynamics from soil respiration measurements

* Gu, L (lianhong-gu@ornl.gov), Oak Ridge National Laboratory, Environmental Sciences Division Building 1509, MS-6335, Oak Ridge, TN 37831, United States Hanson, P (hansonpj@ornl.gov), Oak Ridge National Laboratory, Environmental Sciences Division Building 1509, MS-6335, Oak Ridge, TN 37831, United States Post, M (postwmiii@ornl.gov), Oak Ridge National Laboratory, Environmental Sciences Division Building 1509, MS-6335, Oak Ridge, TN 37831, United States

Our previous study established that it is not reliable to estimate the temperature sensitivity of soil organic matter decomposition directly from soil respiration measurements. Arbitrary values of temperature sensitivity can be obtained because of the convolution between the dynamics of fast turnover carbon pools and the temporal progression in environmental factors. This problem is behind many controversies concerning roles of soil carbon in climate change. Here we introduce a novel approach to analyzing soil respiration measurements that overcomes this problem. The new approach is called 'Localized Ratio Fitting' (LRF). LRF takes advantage of different time scales involved in soil carbon pool dynamics and variations in environmental factors. Through model simulation, we show that LRF can accurately retrieve the real temperature sensitivity of soil organic matter decomposition. Furthermore, we demonstrate that once the temperature sensitivity is properly accounted for, soil respiration measurements can be used to infer the dynamics of litter inputs to soil carbon pools. Therefore, LRF will not only improve the reliability in the interpretation of soil respiration measurements but also expand the application of these measurements.

B41C-0639 

Nature and Nurture in the Continuum of Carbon, Nitrogen and Phosphorus from Litter to Soil Organic Matter in Canadian Forests

* Moore, T (tim.moore@mcgill.ca), Geography, McGill University 805 Sherbrooke St. W., Montreal, QC H3A 2K6, Canada Trofymow, T (ttrofymow@pfc.forestry.ca), Pacific Forestry Centre, Canadian Forest Service 506 West Burnside Road, Victoria, BC V8Z 1M5, Canada Prescott, C (Cindy.Prescott@ubc.ca), Faculty of Forestry, University of British Columbia, Vancouver, BC V6T 1Z4, Canada Titus, B (BTitus@pfc.cfs.nrcan.gc.ca), Pacific Forestry Centre, Canadian Forest Service 506 West Burnside Road, Victoria, BC V8Z 1M5, Canada Working Group, C (ttrofymow@pfc.forestry.ca), Pacific Forestry Centre, Canadian Forest Service 506 West Burnside Road, Victoria, BC V8Z 1M5, Canada

We examine the changes in carbon (C), nitrogen (N) and phosphorus (P) as 10 foliar litters decompose at 21 sites across Canada over 12 years and evaluate the influence of litter quality (nature) and forest floor (nurture) on these changes by applying a stoichiometric approach. Based on all litters and sites, net N loss from the litters occurs at C:N quotients of between 33 and 68, positively correlated with the quotient in the original litter. Net P loss likely occurs at C:P quotients between 800 and 1200. The influence of site on loss of N and P in the litters, relative to C, was evaluated by comparing N and P at 50% original C remaining and showed a weak negative relationship: that is, the higher the soil C:N or C:P quotient in the forest floor, the smaller amount of initial N or P remaining at 50% C remaining. C:N quotients in the original litters ranged from 39 to 83 and show a convergence to an average quotient of 25 when the litters reach 20% original C remaining. When separated into individual litters, those with high initial quotients (cedar and tamarack) showed the most rapid decline in C:N. The differentiation in C:N quotient among the 21 sites is weaker. Initial litter C:P quotients ranged from 369 to 2122 and also showed a convergence, to an average of 427 at 20% original C remaining and there was also a weak differentiation among the sites. Initial N:P quotients ranged from 5 to 26 and converged to an average of 17 at 20% original C remaining. There is a similarity of transformations of C, N and P leading to an average ratio of 427:17:1 when litters have 20% C remaining.

B41C-0640 

Coarse woody debris dynamics: revisiting a boreal black spruce chronosequence

* Bond-Lamberty, B (bpbond@wisc.edu), University of Wisconsin-Madison, Forest Ecology and Management 1630 Linden Drive #120, Madison, WI 53706, United States Gower, S T (stgower@wisc.edu), University of Wisconsin-Madison, Forest Ecology and Management 1630 Linden Drive #120, Madison, WI 53706, United States

We re-visited a seven-stand boreal chronosequence west of Thompson, Manitoba, Canada, in which coarse woody debris (CWD) and its instantaneous decomposition were measured in 2000. New CWD levels and tree and snag fall rates were measured in 2007, and the resulting data used to evaluate how well CWD changes can be modeled using one- and three-pool decay class models. Thus this study compared three independent measures of decomposition (k): direct measurements of CWD respiration; rates based on a seven-year resampling effort; and rates inferred from the chronosequence progression itself. Measured CWD was between 3.3 and 80.4 Mg ha^-1, with the lowest and highest values in the 77- and 18-year-old stands, respectively. Spatial variability was high, and thus at most stands CWD levels had not changed significantly from 2000 to 2007. Snag fall rate varied by an order of magnitude, from 1.4% yr^-1 in the 43-year-old stand to 10.4% yr^-1 in the 12-year-old stand. A one-pool model based on these inputs underestimated actual 2000-2007 CWD decomposition, implying that fragmentation was at least as important a process as heterotrophic respiration; the mean overall k was 0.08 for most stands. The three-pool model was hampered by limited data on decay class transition rates and performed no better than the one-pool model. Although the computed k values implied a failure in chronosequence site selection for at least one site, the overall CWD trend was consistent with a larger number of sites surveyed in the region.

B41C-0641 

Quantifying carbon dioxide fluxes from photodegrading plant litter in arid ecosystems

* Brandt, L A (brand142@umn.edu), University of Minnesota Department of Ecology, Evolution and Behavior, 100 Ecology Building 1987 Upper Buford Circle, Saint Paul, MN 55108, United States Bohnet, C (cmohni@uni.edu), University of Northern Iowa Department of Biology, 144 McCollum Science Hall, Cedar Falls, IA 50614, United States King, J Y (jyking@umn.edu), University of Minnesota Department of Soil, Water, and Climate, 439 Borlaug Hall 1991 Upper Buford Circle, Saint Paul, MN 55108, United States

Biogeochemical models fail to fully explain patterns of litter decomposition in arid ecosystems. Previous research in arid ecosystems has demonstrated that photodegradation, the break-down of chemical compounds by solar radiation, can account for a significant proportion of surface litter mass loss in these ecosystems. However, little is known about the mechanisms of this mass loss. We investigated the potential for solar radiation to lead to direct mineralization to carbon dioxide (CO₂) in 5 litter species native to both arid and mesic ecosystems that receive high levels of solar radiation. In one experiment, we exposed litter to a factorial design of ultraviolet (UV) radiation (UV+, UV-), and sterilization (sterile, non-sterile) over a 10 week period in the lab under dry conditions. Over the ten week period, the only significant effect on CO₂ emissions was due to UV exposure, with UV+ treatments producing 6 times the amount of CO₂ produced under the UV- treatments. CO₂ production rates remained constant over the 10 week period, following a zero order decay model. In a second experiment, we exposed litter of one species to natural solar radiation outdoors on clear, sunny days close to the summer solstice in Minnesota. Our emission rates were seven times higher under natural radiation than under lamps in the lab, possibly due to increased temperature and higher radiation intensity. We found that UV radiation accounted for the largest proportion (47%) of photochemically-induced CO₂ emissions, while shortwave visible radiation (<500 nm) accounted for 38% of CO₂ emissions. A small percentage (15%) was due to wavelengths longer than 500 nm. Production of CO₂ under natural radiation averaged 13 mg C m^-2 d^-1 on clear sunny days. Assuming a linear relationship between total solar irradiance and CO₂ production, we estimate that CO₂ production via photodegradation is between 3.5 and 7 g C m^-2 y^{- 1} in arid ecosystems in the southwestern USA. Taken together with low levels of litter production, our estimates suggest that photochemical mineralization to CO₂ could account for as much as 20% of annual litter mass loss in arid ecosystems. Therefore, abiotic CO₂ production through photodegradation may be a major process by which carbon is lost from plant litter.

B41C-0642 

Forest type affects the influence of harvest on annual and cumulative litter decay in forest and wetland sites across Canada.

* Trofymow, J A (ttrofymow@pfc.forestry.ca), Natural Resources, Canadian Forest Service, 506 Burnside Rd. W., Victoria, BC V8Z 1M5, Canada Thompson, E), Environment Canada – Climate Research Br., 11 Innovation Blvd, Saskatoon, SK S7N 3H5, Canada Cameron, A), Natural Resources, Canadian Forest Service, 1219 Queen Street E, Sault Ste. Marie, ON P6A 5M7, Canada Pare, D), Ressources Naturelles, Service Canadien des Forêts, 1055 rue du P.E.P.S, Ste-Foy, QC G1V 4C7, Canada Lavigne, M), Natural Resources, Canadian Forest Service, Regent St. S, Fredericton, NB E3B 7P7, Canada Flanagan, L), Dept. Biological Sciences, Univ. Lethbridge, Lethbridge, AB T1K 3M4, Canada Moore, T), Dept. Geography, McGill University, Montreal, QC H3A 2K6, Canada Amiro, B), Dept. Soil Science, Univ. Manitoba, Winnipeg, MB V8Z 1M5, Canada Smyth, C), Natural Resources, Canadian Forest Service, 506 Burnside Rd. W., Victoria, BC V8Z 1M5, Canada

A litter decomposition study was established in 16 sites at 7 stations of the Fluxnet Canada Research Network. These sites included paired mature and clearcut forest sites at 5 upland stations (BC, SK, ON, QC, NB) as well as one site at each of two wetland stations (AW, QW) . All sites are instrumented for in situ measurements of soil moisture and temperature. Litterbags were prepared using one of four standard material types (aspen leaves - AL, black spruce needles BS, Douglas fir needles DF and birch wood sticks BW). Six replicate plots were located at each site, each plot contained sufficient numbers of surface litterbags of each material type to allow for four annual collections (2004 – 2007). As well unconfined birch chopsticks were placed at three depths down the soil profile (surface, 5cm, 15cm) and replaced annually to examine the effects of interannual variability on decay. Cumulative litter decay after three years litters rank by % mass remaining had AL<BS<DF<BW and most litters decay more rapidly in clearcut than forests, other than birchwood at one site (QC). Decay of surface birch sticks were similar and interannual variability was less than variability down the soil profile. The effects of clearcut varied with forest site type, on wetter sites surface BW decayed faster in clearcuts than closed forest, however this was reversed in drier forest site types. At lower soil depths on drier sites, decay was more rapid in clearcuts than closed forest. Work is continuing to relate insitu microclimates to decay rates.

B41C-0643 

The Impact of Invasive Earthworm Activity on Biopolymer Character of ýDecayed Litter ý

* Filley, T (filley@purdue.edu), Purdue University, Department of Earth and Atmospheric Sciences, West Lafayette, IN 47907, United States Crow, S (susanecrow@googlemail.com), Queens University, The Centre for Climate, the Environment, and Chronology (14CHRONO), Belfast, BT9 6AX, Ireland Johnston, C (cliffjohnston@purdue.edu), Purdue University, Crop, Soil and Environmental Sciencesý, West Lafayette, IN 47907, United States McCormick, M (mccormickm@si.edu), Smithsonian Environmental Research Centerý, SERC, Edgewater, MD 21037- 0028, United States Szlavecz, K (szlavecz@jhu.edu), The Johns Hopkins University, Dept. of Earth and Planetary Sciences, Baltimore, MD 21218, United States

Over the last 400-500 years invasive European earthworm populations have ýmoved steadily into North American forests either previously devoid of ýearthworms or that contained their own native populations. This has profound ýimpacts upon litter decay and soil organic matter dynamics. To determine the ýimpact of earthworm activity on the biopolymer and stable isotope chemistry of ýlitter residues and the nature of organic carbon moved to the soil profile we ýanalyzed tulip poplar leaves from a multi-year addition experiment in open ýsurface decay litter and litter bag decay experiments, as well as the associated ýsoils among forest plots that varied in non-native earthworm density and ýbiomass. The chemical alteration of biopolymers was tracked with FTIR ýspectroscopy, 13C-TMAH thermochemolysis, alkaline CuO extraction, and stable ýisotope mass spectrometry. Earthworm activity resulted in residues and soil ýparticulate organic matter depleted in cuticular aliphatic components and ýpolyphenols but highly enriched in ether-linked lignin with respect to initial litter ýmaterial. Decay in low earthworm abundance plots, as well as all experiments ýwith earthworm-excluding litter bags, resulted in enrichment in cutin aliphatics ýand only minor increases in ether linked lignin phenols which was also reflected ýin the soils below the amendments. Additionally, the stable carbon and nitrogen ýisotope composition of tulip poplar residues became isotopically distinct. The ýresults from litter bag decays were only reflective of the chemistry at sites with ývery low earthworm abundances. ý

B41C-0644 

Soil CO2 Emissions: Changes in effective diffusivity due to sustained winds

* Nickerson, N (nnickers@stfx.ca), St. Francis Xavier University, P.O. Box 5000, Antigonish, NS B2G 2W5, Canada Risk, D (drisk@stfx.ca), St. Francis Xavier University, P.O. Box 5000, Antigonish, NS B2G 2W5, Canada

Soils are the largest terrestrial source of CO2 to the atmosphere and a crucial component in the global carbon balance. Through soil profile and surface monitoring of CO2 concentrations and fluxes it has been shown that soil physical parameters such as moisture and structure can exert strong control over soil CO2 production, storage and emissions. Often, this control is a result of changes in the gas transport potential, or effective diffusivity, of the soil matrix. Variations in wind speeds near the soil surface can induce pressure fluctuations and changes in the structure of the boundary-layer which may lead to changes in effective diffusivity. Sustained winds have the potential to alter both the concentrations of gas in the soil as well as the fluxes of gas to and from the soil matrix. Gas emissions studies at air-water interfaces have demonstrated these effects, showing clear correlations between wind speed and pCO2 but similar research has not been conducted to examine the subsurface effects of wind across the soil-atmosphere interface. A clear understanding of these processes will be critical to understand how they affect flux monitoring strategies as well as to enhance the current understanding of soil CO2 production and emissions. Using fans to generate artificial winds between 3 and 30 km/h and solid state CO2 sensors we examine changes in soil profile CO2 concentrations both in lab conditions using artificial soils with no vegetation and in field conditions under sparse grass cover. Preliminary results show that in both laboratory and field experiments, soil CO2 concentrations are lowered by 10-80% within 20 minutes of the wind speed change. Furthermore, after the fans are shut off, CO2 concentrations recover quickly to their original state implying that there is little change in microbial CO2 production and that the observed CO2 depletion is a result of changes in effective diffusivity. Estimates of the change in effective diffusivity range between 2 and 10 times the original diffusivity of the medium and show a positive, exponential dependence on wind speed. Results from this study will be applicable to measurement and monitoring of soil respired CO2 and to enhancing the understanding of physical constraints on soil C cycling.

B41C-0645 

Analysis of Changes in Biochemical Composition Under Free-Air CO₂ enrichment by ¹³C Nuclear Magnetic Resonance: Leaf Litter, Roots, and Soils From Oak Ridge

* Hockaday, W C (bill.hockaday@rice.edu), Rice University, Department of Earth Science, P.O. Box 1892, Houston, TX 77251, United States Masiello, C A (masiello@rice.edu), Rice University, Department of Earth Science, P.O. Box 1892, Houston, TX 77251, United States Baldock, J A), CSIRO Land and Water, PMB #2, Glen Osmond, SA 5064, Australia Iversen, C M (civersen@utk.edu), University of Tennessee, Department of Ecology and Evolutionary Biology, 569 Dabney Hall, Knoxville, TN 37996, United States Norby, R J (rjn@ornl.gov), Oak Ridge National Lab, One Bethel Road, Building 1062, Oak Ridge, TN 37831, United States

Changes in plant biochemistry as a result of increasing atmospheric carbon dioxide concentration [CO₂] influence the cycling of the terrestrial carbon pool and thereby constitute a climate feedback. We have investigated molecular-level changes in the chemical composition of the organic carbon pool of a deciduous forest in Oak Ridge, Tennessee, after 9 years of free-air CO₂ enrichment. We employ a novel approach based upon solid-state ¹3C nuclear magnetic resonance (NMR) analysis and application of a molecular mixing model. This method generates quantitative estimates of total lipids, proteins, carbohydrates, and lignin. ¹³C NMR spectra were acquired for acid-insoluble soil organic matter from depths of 0 – 5 cm and 5 – 15 cm in two ambient and two elevated [CO₂] treatments. In the upper 5 cm, elevated [CO₂] soils show a 7% increase in lignin, while lipids and proteins decrease by approximately 10%. Below 5 cm, soil lipid content decreased by 15% relative to ambient [CO₂] soils. Changes in the composition of the SOM pool may be attributed to changes in plant biochemistry under elevated [CO2]. Therefore we have performed ¹³C NMR analysis of major aboveground and belowground biomass inputs: senesced leaves and fine roots (<1 mm diameter). Significant [CO₂] effects on root chemistry are observed. Based upon these data, we are able to make a preliminary assessment of the contributions of leaf C and root C to changes in the molecular composition of the SOM pool.

B41C-0646 

Decomposition of Soil Organic Matter From Physically Derived Decay Rates

* Forney, D C (dforney@mit.edu), Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, * Forney, D C (dforney@mit.edu), Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, Rothman, D H (dhr@mit.edu), Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139,

The decomposition of organic matter in soils and marine sediments exhibits both marked similarities and unmistakable differences [1]. Despite obvious chemical and biological complexity, a surprisingly simple physical model captures the dynamics of decay in a wide variety of sediments [2]. This physical model consists of a porous reaction-diffusion system where a wide distribution of reaction rates derives purely from microbial accessibility and diffusion-limited enzymatic hydrolysis. Here we consider whether such a model can be similarly applied to the late stages of organic matter decay in soils where microbes degrade recalcitrant substrates. We consider the presence of both bacteria and fungal hyphae. Predictions from the model are found to fit over 30 litter and soil carbon data sets. The similarity between the temporal decay of natural organic matter with the evolution of this simple physical system indicates that diffusion-limitation may be a common characteristic of detrital decay in both soils and sediments. It also reiterates the importance of the substrate structure in the microbial decomposition of organic matter. [1] J.~I Hedges, J.~M. Oades, Org. Geochem. 27, 319 (1997). [2] D.~H. Rothman, D.~C. Forney, Science 316, 1325 (2007).

B41C-0647 

Biochemical Control of Fungal Biomass and Enzyme Production During Native Hawaiian Litter Degradation

* Amatangelo, K L (kamatang@stanford.edu), Stanford University, Department of Biological Sciences, Stanford, CA 94309, Cordova, T P (cordovap@stanford.edu), Stanford University, Department of Biological Sciences, Stanford, CA 94309, Vitousek, P M (vitousek@stanford.edu), Stanford University, Department of Biological Sciences, Stanford, CA 94309,

Microbial growth and enzyme production during decomposition is controlled by the availability of carbon substrates, essential elements, and the ratios of these (such as lignin:N). We manipulated carbon:nutrient stoichiometry during decomposition using a natural fertility gradient in Hawaii and litter of varying initial biochemistry. We collected freshly senesced litter of seven biochemically distinct species from three sites offering differing levels of N, P, cations, and ¹⁵N , but similar yearly rainfall and temperature patterns. Litter types were decomposed at both the sites they were collected, and at the other site(s) that species was found. Litter was collected at multiple time points, and after one year of decomposition, calculated K constants varied an order of magnitude, from 0.276 to 2.76. Decomposition rates varied significantly with both litter site of origin and deployment, except at the oldest, P-limited site, where litter site of origin was not significantly correlated with decomposition within species. As microbial exocellular enzymes provide the catalyst for the breakdown of organic molecules including phenols, cellulose, and cutin, we assayed polyphenol oxidase, cellobiohydrolase, cutinase, chitinase, and lignin peroxidase to evaluate the breakdown sequence of different litter types. To measure the fungal biomass accumulating during decomposition, we extracted (22E)-Ergosta-5,7,22-trien-3beta- ol (ergosterol) on a subset of samples. The production of particular exocellular enzymes on litter species responded distinctly to origin and decomposition sites: after six months, chitinase and cellobiohydrolase were significantly affected by origin site, whereas polyphenol oxidase activity was controlled by deployment site. We conclude that site characteristics can alter the interaction between litter carbon:nutrient ratios and decomposition rate, mediated through microbial biomass and enzyme production.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.