Wednesday, August 4, 2010: 10:10 AM
407, David L Lawrence Convention Center
Background/Question/Methods Plant litter chemistry influences soil organic matter dynamics, nutrient cycling, and soil carbon storage and conceptual models predict that changes in litter chemistry during decomposition are primarily dependent upon initial litter composition and the extent of decomposition. Far less is known about whether decomposer community structure and land use management regimes – including the conversion of grasslands to biofuel crop production – can also change litter chemistry during decomposition. Our objectives were to determine: 1) the potential effects of agricultural intensification on plant litter chemistry and decomposition rates; and 2) to relate ecosystem management effects on litter chemistry and decomposition rates to decomposer communities. A litterbag experiment was conducted over one growing season (108 days) using corn and grass (primarily Bromus inermis) leaf litter. At weekly to monthly time intervals we measured decomposition rates (mass loss), hydrolytic and oxidative enzyme activities, microarthropod community composition, bacterial and fungal relative abundance (qPCR), and changes in litter chemistry in replicated conventional till, no-till, and old field communities at the W.K. Kellogg Biological Station LTER. Litter chemistry was determined at time zero and after 108 days of decomposition using pyrolysis-gas chromatography/mass spectroscopy.
Results/Conclusions After one growing season, conventional-till litter decomposition rates were 20% greater than old field decomposition, however, no-till decomposition rates were not significantly different from old field or conventional till. After decomposition, grass residue in conventional- and no-till systems was enriched in total polysaccharides relative to the initial litter, while grass litter in old fields was enriched in nitrogen-bearing compounds and lipids. These differences corresponded with differences in decomposer communities, which also exhibited strong responses to litter type that varied with management. Our results show that agricultural intensification can increase litter decomposition rates, alter decomposer communities, and shift litter chemistry in ways that could have long-term effects on soil organic matter dynamics. We propose that future efforts to predict soil C dynamics should consider that changes in litter chemistry during decomposition are not only a function of initial litter quality and mass loss but are also influenced by the specific metabolic capabilities of decomposer communities.
Results/Conclusions After one growing season, conventional-till litter decomposition rates were 20% greater than old field decomposition, however, no-till decomposition rates were not significantly different from old field or conventional till. After decomposition, grass residue in conventional- and no-till systems was enriched in total polysaccharides relative to the initial litter, while grass litter in old fields was enriched in nitrogen-bearing compounds and lipids. These differences corresponded with differences in decomposer communities, which also exhibited strong responses to litter type that varied with management. Our results show that agricultural intensification can increase litter decomposition rates, alter decomposer communities, and shift litter chemistry in ways that could have long-term effects on soil organic matter dynamics. We propose that future efforts to predict soil C dynamics should consider that changes in litter chemistry during decomposition are not only a function of initial litter quality and mass loss but are also influenced by the specific metabolic capabilities of decomposer communities.