B44A-01 

Developing a General Understanding of the Decomposition Process: Results From a Network Experiment

* Harmon, M E (mark.harmon@oregonstate.edu), Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331-5752,

Although leaf and fine root litter undergo many changes during the process of decomposition, there is relatively little long-term data to develop a general, global level understanding of this process. The LIDET (Long-term Intersite Decomposition Experiment Team) study, conducted at 27 sites in North and Central America using a wide range of litter types, created a database suitable for this purpose. Analysis of the long-term pattern of mass loss indicated that while a slower, later phase of decomposition occurred in most cases for a substantial fraction (30%) it did not. These results imply that average long-term decomposition rates may be overestimated by up to a factor of 2 if based on short-term (1 year) decomposition losses. The relationship between wooden dowel decomposition and climatic indices indicated limits on the ability to predict decomposition rates for sites more favorable for decomposition, with a maximum coefficient of determination of 70%. Regression analysis of the relationship between climatic and substrate quality indices and decomposition rates indicated controls on decomposition processes changed from the early to late stages, with early-stage processes controlled by climate and initial litter chemistry, but late-stage processes more likely controlled by other factors such as the soil environment. Development of a mechanistic model based on AIC analysis indicates at least 3 litter fractions need to be considered and that a climatic index that combines the effects of temperature and moisture explains the most variation (70%). Analysis of the relationship between nitrogen release and mass loss indicated a global relationship exists that is largely dependent on the initial nitrogen content with 77% of the variation explained by this simple model. Overall the LIDET study indicated that there are general global patterns to long- term decomposition dynamics, however, current models indicate limits to our ability to predict global patterns of this important process.

B44A-02 INVITED 

Results from a Long-term Litter Decomposition Experiment in Canadian Forests and Their Use in Soil Carbon Model Verification and Development.

* Trofymow, J A (ttrofymow@pfc.forestry.ca), Natural Resources, Canadian Forest Service, 506 Burnside Rd. W., Victoria, BC V8Z 1M5, Canada Smyth, C), Natural Resources, Canadian Forest Service, 506 Burnside Rd. W., Victoria, BC V8Z 1M5, Canada Moore, T), Dept. Geography, McGill University, Montreal, QC H3A 2K6, Canada Prescott, C), Dept. Forest Science, Univ. British Columbia, Vancouver, BC V6T 1Z4, Canada Titus, B), Natural Resources, Canadian Forest Service, 506 Burnside Rd. W., Victoria, BC V8Z 1M5, Canada Siltanen, M), Natural Resources, Canadian Forest Service, 5320 122 St., Edmonton, AB T6H 3S5, Canada Visser, S), Dept. Biological Sciences, Univ. Calgary, Calgary, AB T2N 1N4, Canada Preston, C), Natural Resources, Canadian Forest Service, 506 Burnside Rd. W., Victoria, BC V8Z 1M5, Canada Nault, J), Natural Resources, Canadian Forest Service, 506 Burnside Rd. W., Victoria, BC V8Z 1M5, Canada Nault, J), Faculte' de Foresterie et a` de Geomatique, Univ. Laval, Quebec City, QC G1K 7P4, Canada Camire', C), Faculte' de Foresterie et a` de Geomatique, Univ. Laval, Quebec City, QC G1K 7P4, Canada Fyles, J), MacDonald College, McGill University, Ste Anne de Bellevue, QC H9X 1C0, Canada Kozak, L), Agriculture Agri-Food Canada, CLBRR/LRD, Univ. Saskatchewan, Saskatoon, SK S7N 5A8, Canada Kranabetter, M), British Columbia Ministry of Forests, Bag 600, Smithers, BC V0J 2N0, Canada Kutny, L), Inuvik Research Centre, P.O. Box 1430, Inuvik, NW X0EOTO, Canada Morrison, I), Natural Resources, Canadian Forest Service, 1219 Queen St. East, Sault Ste. Marie, ON P6A 5M7, Canada Smith, S), Agriculture Agri-Food Canada, Highway 97, Summerland, BC V0H 1Z0, Canada Wein, R), Faculty Agriculture and Forestry, Univ. Alberta, Edmonton, AB T6G 2P5, Canada White, D), Forest Management Branch, Energy, Mines and Resources, 345 300 Main St., Whitehorse, YK Y1A 2B5, Canada

Climate and substrate quality have been shown to be key determinants of rates of litter decomposition, though other site factors can be important under certain conditions. The Canadian Intersite Decomposition Experiment (CIDET) was established in 1992 with the objective of providing data on the long-term rates of litter decomposition and nutrient mineralization for a range of forested ecoclimatic regions in Canada. Such data were needed to help verify the Carbon Budget Model - Canadian Forest Sector (CBM-CFS) used for national C accounting, as well as aid in the development of other soil C models. CIDET examined the annual decay, over a 12-year period from 1993 to 2004, of 10 standard foliar litters and 2 wood substrates at 18 forested upland and 3 wetland sites ranging from the cool temperate to subarctic regions. On a subset of sites and litter types, changes in litter C chemistry over time were also determined. Over the first 6 years, C/N ratio and iron increased, NMR showed an overall decline in O-alkyl C (carbohydrates) and increase in alkyl, aromatic, phenolic, and carboxyl C. Proximate analysis showed the acid unhydrolyzable residue (AUR) increases, but true lignin does not accumulate, in contrast to the conceptual ligno-cellulose model of decomposition. Overall litter decay during first phase of decomposition was related to initial litter quality (AUR and water soluble extract), winter precipitation, but not temperature. Decay rate "k" during second phase was related to temperature, initial litter quality (AUR and AUR/N), summer precipitation, but not soil N. In most cases decay had approached an asymptote before end of experiment, although decay rates during this semistable phase were low and difficult to quantify. However, the asymptotes were related to temperature suggesting decay in this phase is temperature dependant. Asymptotes were also related to summer precipitation and forest floor pH and C/N ratio. Comparisons of CIDET 12 year C mass remaining data with CBM-CFS3, showed default model predictions of C remaining were generally too low. Predicted base decay rate was higher than observed for most litter types but the default Q10 value was within the range of observed values. Model optimization to the data reduced absolute error by half. Other climate or site variables that could be used to improve the fit of CBM-CFS3 and fit of CIDET data with other soil C models will be discussed.

B44A-03 

A Simple Three Pool Model Accurately Describes Patterns of Long-term Litter Decomposition in Diverse Climates Across Two Continents

* Adair, E (adair016@umn.edu), Departments of Ecology, Evolution, and Behavior and Forest Resources, University of Minnesota, 1987 Upper Buford Circle, Saint Paul, MN 55108, United States Parton, W J (billp@warnercnr.colostate.edu), Natural Resource Ecology Laboratory, and Graduate Degree Program in Ecology, Colorado State University, 2nd Floor, 1231 East Drive, Fort Collins, CO 80523, United States Del Grosso, S J (delgro@warnercnr.colostate.edu), Natural Resource Ecology Laboratory, and Graduate Degree Program in Ecology, Colorado State University, 2nd Floor, 1231 East Drive, Fort Collins, CO 80523, United States Silver, W L (wsilver@nature.berkeley.edu), Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, 137 Mulford Hall #3114, Berkeley, CA 94720, United States Harmon, M E (mark.harmon@oregonstate.edu), Department of Forest Sciences, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, United States Hall, S A (shall@tnc.org), The Nature Conservancy, North Central Washington Field Office, Wenatchee, WA 98801, United States Burke, I C (indy@warnercnr.colostate.edu), Department of Forest, Rangeland, and Watershed Stewardship, and Graduate Degree Program in Ecology, Colorado State University, 1401 Campus Delivery, Fort Collins, CO 80523, United States Hart, S C (steve.hart@NAU.EDU), School of Forestry and Merriam-Powell Center for Environmental Research, Northern Arizona University, POB 15018, Flagstaff, AZ 86011, United States

As atmospheric CO₂ increases, ecosystem carbon sequestration will largely depend on how global changes in climate will alter the balance between net primary production and decomposition. The response of primary production to climatic change has been examined using well-validated mechanistic models, but the same is not true for decomposition, a primary source of atmospheric CO₂. We used the Long-term Intersite Decomposition Experiment Team (LIDET) data set and model selection techniques to choose and parameterize a model that describes global patterns of litter decomposition. Mass loss was best represented by a three pool negative exponential model, with a rapidly decomposing labile pool, an intermediate pool representing cellulose, and a recalcitrant pool. The initial litter lignin/nitrogen ratio defined the size of labile and intermediate pools. Lignin content determined the size of the recalcitrant pool. The decomposition rate of all pools was modified by climate, but the intermediate pool's decomposition rate was also controlled by relative amounts of litter cellulose and lignin (indicative of lignin-encrusted cellulose). The effect of climate on decomposition was best represented by a composite variable that multiplied a water stress function by the Lloyd and Taylor (1994) variable Q10 temperature function. Although our model explained nearly 70% of the variation in the LIDET data, we observed systematic deviations from model predictions. Below- and aboveground material decomposed at notably different rates, depending on the decomposition stage. Decomposition in certain ecosystem-specific environmental conditions was not well represented by our model; this included roots in very wet and cold soils, and aboveground litter in N-rich and arid sites. Despite these limitations, our model may still be extremely useful for global modeling efforts, because it accurately (R² = 0.6804) described general patterns of long-term global decomposition for a wide array of litter types, using relatively minimal climatic and litter quality data.

B44A-04 INVITED 

The leaf economic spectrum drives litter decomposition within regional floras worldwide

* Cornwell, W K (wcornwell@gmail.com), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Cornelissen, J H), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Amatangelo, K), Stanford University, Biological Sciences, Stanford, CA 94305, United States Dorrepaal, E), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Eviner, V), University of California, Davis, Plant Sciences, Davis, CA 95616, United States Godoy, O), Universidad de Alcalá, Facultad de Cienceias, Madrid, Madrid, Spain Hobbie, S E), University of Minnesota, Dept of Ecology, St Paul, MN 55108, United States Hoorens, B), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Kurokawa, H), Landcare Research, PO Box 40, Lincoln, 7640, New Zealand Kurokawa, H), Tohoku University, Graduate School of Life Sciences, Sendai, 980-8578, Japan Perez Harguindeguy, N), Universidad Nacional de Córdoba, Instituto Multidisciplinario do Biología Vegetal, Córdoba, CC495 5000, Argentina Quested, H M), Stockholm University, Dept of Botany, Stockholm, S106 91, Sweden Santiago, L S), University of Colifornia, Riverside, 2150 Batchelor Hall, Riverside, CA 92521, United States Wardle, D A), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Wardle, D A), Landcare Research, PO Box 69, Lincoln, Lincoln, New Zealand Wright, I J), Macquarie University, Dept. of Biological Sciences, Sydney, NSW 2109, Australia Aerts, R), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Allison, S), University of California, Irvine, Dept of Ecology and Evolutionary Biology, Irvine, CA 92697, United States van Bodegom, P), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Brovkin, V), Potsdam Institute for Climate Impact Research, Climate Systems Research Dept, Potsdam, 14412, Germany Chatain, A), Monash University, School of Biological Sciences, Clayton, VIC 3800, Australia Callaghan, T), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Callaghan, T), Sheffield University, Dept of Animal and Plants Sciences, Sheffield, S10 2TN, United Kingdom Díaz, S), Universidad Nacional de Córdoba, Instituto Multidisciplinario do Biología Vegetal, Córdoba, CC495 5000, Argentina Garnier, E), Universidad Nacional de Córdoba, Instituto Multidisciplinario do Biología Vegetal, Córdoba, CC495 5000, Argentina Garnier, E), Centre d'Ecologie Fonctionnelle et Evolutive, 1919 route de Mende, Montpellier, Cedex5, France Gurvich, D E), Universidad Nacional de Córdoba, Instituto Multidisciplinario do Biología Vegetal, Córdoba, CC495 5000, Argentina Kazakou, E), Centre d'Ecologie Fonctionnelle et Evolutive, 1919 route de Mende, Montpellier, Cedex5, France Klein, J A), Colorado State University, Dept of Forest, Rangeland, and Watershed Stewardship, Fort Collins, CO 80523, United States Read, J), Monash University, School of Biological Sciences, Clayton, VIC 3800, Australia Reich, P B), University of Minnesota, Department of Forest Resources, St. Paul, MN 55108, United States Soudzilovskaia, N A), Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands Soudzilovskaia, N A), Moscow State University, Dept of Geobotany, Moscow, Moscow, Russian Federation Vaieretti, M V), Universidad Nacional de Córdoba, Instituto Multidisciplinario do Biología Vegetal, Córdoba, CC495 5000, Argentina Westoby, M), Macquarie University, Dept. of Biological Sciences, Sydney, NSW 2109, Australia

Leaves are the green machines that drive terrestrial oxygen production, carbon assimilation and primary productivity worldwide. Some green machines are fast but short-lived producers, while others are durable enough for steady carbon gain over the long term. The nuts and bolts of the green machinery to support fast production versus durability are the chemical, physiological, and structural traits of the plant species that together shape the globally operating "leaf economics spectrum". These green-leaf traits have crucial implications not only for the production of biomass in biogeochemical cycles, but also for its subsequent fate: the litter traits inherited from the green leaves together with the litter environment drive the rate of litter decomposition. From a global synthesis of 818 species in 66 decomposition experiments on six continents, we quantified the degree to which functional differentiation among species affects their litter decomposition rates. For the first time at global scale, we show that: (1) the magnitude of species-driven differences in decomposition within biomes is surprisingly large--often greater than 10-fold (2) the decomposability of a species' litter is consistently correlated with that species' position on the green-leaf economics spectrum: species designed to achieve a fast return on carbon invested in leaves produce faster decomposing litter compared to those species with a slower-return strategy. These results suggest that a shift in relative abundance of particular species traits within a biome could strongly impact overall decomposition rates. Correctly predicting the abundance and distribution of particular plant traits will be crucial for accurate forecasts of future carbon pools and their feedbacks to further climate change. http://www.vegfunction.net/wg/17/17_speciesdecomp.htm

B44A-05 

Stoichiometric and Climatic Controls on Litter Nitrogen Mineralization

* Manzoni, S (sm86@duke.edu), Duke University, Pratt School of Engineering, 121 Hudson Hall, Box 90287, Durham, NC 27708-0287, United States Porporato, A (amilcare@duke.edu), Duke University, Pratt School of Engineering, 121 Hudson Hall, Box 90287, Durham, NC 27708-0287, United States

The release of nitrogen from decomposing plant residues is intimately coupled with its carbon losses through microbial respiration. At a global scale, the availability of C substrates drives the growth of microbial communities and together with their stoichiometry determines the microbial N demand. In turn, microbial demand controls the immobilization or mineralization of N and ultimately the nutrient availability in the soil. A simple mechanistic model of litter decomposition, accounting for chemistry and microbial characteristics (namely microbial C-to-N ratio and respiration rate), allows us to derive analytical N release curves. These curves are used to study the variability of N-release patterns in global-scale datasets from a microbiological perspective. Macroclimate is found to affect the microbial characteristics and hence the N mineralization patterns across biomes, suggesting that altered macroclimate and litter chemistry may affect N availability under climate change scenarios.

B44A-06 

Global patterns in litter decomposition: a synthesis.

* Auch, W E (wauch@uvm.edu), University of Vermont, 105 Carrigan Drive, Burlington, VT 05405, United States Ross, D S (dross@uvm.edu

Leaf and coarse woody debris (LCWD) decay catalyzes the biochemical mechanisms of the soil-aboveground interface, and should be an important component of climate change models that address carbon and nitrogen. There is a clear need for the identification of determinant climate or litter chemistry parameters at the global scale. Local and global decay is commonly attributed to litter chemistry and climate, respectively. The objective of this synthesis was to illustrate LCWD decay across a global climate-chemistry continuum and contrast results with a previous assessment via both standard first-order (|k|) decay kinetics and gradient exponent values arranged in order of influence from initial to latter decay stages. Results suggest greater initial LCWD cation concentrations yielded the fastest initial rates of decomposition and most climatic indices appeared relevant at intermediate stages of decay. Elevation and refractory LCWD carbon (i.e. carbon, lignin, and tannins) were inversely correlated with decay, prolonging the process and possibly acting in concert as "end-point" determinants. Furthermore, the initial influence of nitrogen and phosphorus is universal across LCWD-type as well as ecoregion. Climate acts in a transitional role between easily solubilized and late or aromatic substrate decay. Global and continental carbon cycling assumptions and models must acknowledge: i) the influence of LCWD cation and N concentration during initial fragmentation, leaching, and transformation; ii) climate, specifically seasonal temperature averages > evapotranspiration > precipitation, during the interim; and iii) the ever-present influence of seasonality and litter aromatic components. Key Words: Leaf and Coarse Woody Debris (LCWD) decomposition, |k|, first-order kinetics, Carbon Cycle, Global Climate Change (GCC), Actual Evapotranspiration (AET).

B44A-07 

Climate Induced Changes in Global-Scale Decomposition Over the Last Hundred Years

* Silver, W L (wsilver@nature.berkeley.edu), University of California, Berkeley, Ecosystem Sciences 137 Mulford Hall #3114 University of California, Berkeley, CA 94720, United States Parton, W J (billp@nrel.colostate.edu), Natural Resource Ecology Lab, Colorado State University, 200 W. Lake, Campus Mail 1499, Fort Collins, CO 80523-1499, United States Riley, T (triley@nrel.colostate.edu), Natural Resource Ecology Lab, Colorado State University, 200 W. Lake, Campus Mail 1499, Fort Collins, CO 80523-1499, United States

Litter decomposition represents the largest annual flux of carbon from terrestrial ecosystems, and is highly sensitive to climate. Using a climate-decomposition index we demonstrate significant changes in litter decomposition rates globally over the last 100 years. Litter decomposition increased by 18% from 40-60 °N and by 29% from 20-40 °S latitude. The greatest relative increases in decomposition were in deserts (+23%), grasslands (+21%), and coniferous forests (+19%). Tropical forest decomposition decreased slightly (-2%). Contrary to expectations, the relative change in decomposition was more sensitive to precipitation than temperature. Results highlight decomposition hotspots that represent significant feedbacks to climate change.

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