Leaf litter diversity alters microbial activity, microbial abundances, and nutrient cycling in a subtropical forest ecosystem
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Human activities affect both tree species composition and diversity in forested ecosystems. This in turn alters the species diversity of plant litter and litter quality, which may have cascading effects on soil microbial communities and their functions for decomposition and nutrient cycling. We tested microbial responses to litter species diversity in a leaf litter decomposition experiment including monocultures, 2-, and 4-species mixtures in the subtropical climate zone of southeastern China. Soil microbial community composition was assessed by lipid analysis, and microbial functions were measured using extracellular enzyme activity and gross rates of nitrogen mineralization. We observed a positive relationship between litter species diversity and abundances of mycorrhizal fungi and actinomycetes. Alternatively, enzyme activities involved in carbon and phosphorus acquisition, and enzyme indices of relative carbon limitation, were higher only in the 4-species mixtures. This suggests that the minimum basal substrate level for enzyme production was reached, or that limitation was higher, at the highest diversity level only. Responses to litter diversity also changed over time, where phosphatase responses to litter diversity were strongest early in decomposition and the indices of carbon limitation relative to other nutrients showed stronger responses later in decomposition. Enzyme activities were related to lipid biomarker data and the mass of litter remaining at the third time point, but relationships between enzyme activity and the mass of litter remaining were not consistent across other time points. We conclude that litter species richness will likely only reduce microbial functions at key intervals of diversity loss while microbial growth is more sensitive to incremental diversity loss, with no clear relationships between them or to ecosystem functions. The observed litter diversity effects on soil microbial biomass and enzyme activity indicate interactions of aboveground and belowground communities, and together with environmental conditions they are important for maintaining ecosystem functions.
KeywordsEnzyme activity Litter decomposition Litter diversity effects Microbial community composition Nitrogen mineralization rates Subtropical forest
We thank all the members of NILEX group (within Biodiversity and Ecosystem Function-China Project) as well as the field helpers for their efforts for establishing and maintaining the field plots. We thank Yvonne Eckstein and Ann-Kathrin Blank for their help with lipid analysis and Kantida Juncheed for her help in enzyme activity measurement. We thank also Oliver Spott and Bernd Apelt for their help with N mineralization rates measurements. We thank Peter Kühn, Steffen Seitz and Philipp Goebes for providing the basic soil data. This work was funded by German Research Foundation (DFG) (Research Unit FOR 891/2, BU941/24-2, GU 1237/1-1) and by University of Minnesota internal faculty startup funds.
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