Nitrogen deposition effects on soil organic matter chemistry are linked to variation in enzymes,ecosystems and size fractions |
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Authors: | A Stuart Grandy Robert L Sinsabaugh Jason C Neff Martina Stursova Donald R Zak |
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Institution: | (1) Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824, USA;(2) Department of Biology, University of New Mexico, Albuquerque, NM, USA;(3) Department of Geological Sciences, University of Colorado, Boulder, CO, USA;(4) School of Natural Resources & Environment and the Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA |
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Abstract: | Recent research has dramatically advanced our understanding of soil organic matter chemistry and the role of N in some organic
matter transformations, but the effects of N deposition on soil C dynamics remain difficult to anticipate. We examined soil
organic matter chemistry and enzyme kinetics in three size fractions (>250 μm, 63–250 μm, and <63 μm) following 6 years of
simulated atmospheric N deposition in two ecosystems with contrasting litter biochemistry (sugar maple, Acer saccharum—basswood, Tilia americana and black oak, Quercus velutina—white oak, Q. alba). Ambient and simulated (80-kg NO3
−–N ha−1 year−1) atmospheric N deposition were studied in three replicate stands in each ecosystem. We found striking, ecosystem-specific
effects of N deposition on soil organic matter chemistry using pyrolysis gas chromatography/mass spectrometry. First, furfural,
the dominant pyrolysis product of polysaccharides, was significantly decreased by simulated N deposition in the sugar maple–basswood
ecosystem (15.9 vs. 5.0%) but was increased by N deposition in the black oak–white oak ecosystem (8.8 vs. 24.0%). Second,
simulated atmospheric N deposition increased the ratio of total lignin derivatives to total polysaccharides in the >250 μm
fraction of the sugar maple–basswood ecosystem from 0.9 to 3.3 but there were no changes in other size classes or in the black
oak–white oak ecosystem. Third, simulated N deposition increased the ratio of lignin derivatives to N-bearing compounds in
the 63–250 and >250 μm fractions in both ecosystems but not in the <63 μm fraction. Relationships between enzyme kinetics
and organic matter chemistry were strongest in the particulate fractions (>63 μm) where there were multiple correlations between
oxidative enzyme activities and concentrations of lignin derivatives and between glycanolytic enzyme activities and concentrations
of carbohydrates. Within silt-clay fractions (<63 μm), these enzyme-substrate correlations were attenuated by interactions
with particle surfaces. Our results demonstrate that variation in enzyme activity resulting from atmospheric N deposition
is directly linked to changes in soil organic matter chemistry, particularly those that occur within coarse soil size fractions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Nitrogen deposition Enzymes Carbon structure Pyrolysis gas chromatography/mass spectrometry Soil organic matter |
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