COS 125-7 - Litter quality constrains the affect of management intensity on decomposers and litter chemistry

Friday, August 12, 2011: 10:10 AM
5, Austin Convention Center
Kyle Wickings, Natural Resources and the Environment, University of New Hampshire, Durham, NH, A. Stuart Grandy, Department of Natural Resources and the Environment, University of New Hampshire, Durham, NH, Sasha C. Reed, Southwest Biological Science Center, U.S. Geological Survey, Moab, UT and Cory C. Cleveland, Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, MT

Plant litter undergoes predictable changes in chemistry during decomposition that are closely associated with patterns of decomposer activity.  For example, during the initial stages of decomposition soluble and easily decomposed compounds are rapidly lost.  This phase may be associated with peaks in glucosidase and peptidase activities. As labile compounds are removed from litter the relative composition of recalcitrant compounds increases along with the activities of oxidative enzymes.  Although patterns of litter chemistry and decomposer activity are considered robust, they can vary not only among litter types but also among ecosystems with different management intensities during early stages of decomposition.  It is unclear, however, whether the effects of litter quality and management intensity on decomposition dynamics persist beyond early stages of decay.  We conducted a litterbag study to determine the effects of litter quality and management intensity on litter decomposition and decomposer community composition and activity over three growing seasons. Corn and grass leaf litter were decomposed in conventional and no-till agricultural systems and early succession old fields at the Kellogg Biological Station, LTER, Hickory Corners, MI.  During each year we measured litter mass loss and chemistry via pyrolysis-gas chromatography/mass spectroscopy, extracellular enzyme activity (EEA), fungal-bacterial ratios (F:B) and detritivore abundance.


Initially, corn litter had a higher lignin-nitrogen ratio (L:N) than grass.  L:N of corn and grass diverged substantially over time, and corn litter exhibited lower mass loss than grass over three years (75 vs. >95%).  Litter type had strong effects on EEA, F:B and decomposer abundance during three years of decomposition, with grass showing greater hydrolytic enzyme activities and decomposer abundances and lower F:B than corn litter.  Management intensity exhibited considerable effects on biological factors over all three years. Hydrolytic enzyme activities increased with a decrease in management intensity while oxidative enzymes, F:B and decomposer abundance were positively affected.  An increase in management intensity also increased decomposition rates and caused shifts in litter chemistry including increases in polysaccharides and decreases in lipids and N-bearing compounds.  The effects of management intensity on litter chemistry, however, only emerged when litter L:N was lower than 13.  Our study demonstrates that management intensity exerts strong effects on decomposer communities which in turn may result in unique patterns in litter chemistry.  Our findings further suggest that the ability of decomposer communities to alter litter chemistry is constrained by litter quality.

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