Disentangling species and functional group richness effects on soil N cycling in a grassland ecosystem |
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| Authors: | Xiaorong Wei Peter B Reich Sarah E Hobbie Clare E Kazanski |
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| Affiliation: | 1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, China;2. Department of Forest Resources, University of Minnesota, St. Paul, MN, USA;3. Hawkesbury Institute for the Environment, Western Sydney University, Penrith South DC, NSW, Australia;4. Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN, USA |
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| Abstract: | Species richness (SR) and functional group richness (FGR) are often confounded in both observational and experimental field studies of biodiversity and ecosystem function. This precludes discernment of their separate influences on ecosystem processes, including nitrogen (N) cycling, and how those influences might be moderated by global change factors. In a 17‐year field study of grassland species, we used two full factorial experiments to independently vary SR (one or four species, with FGR = 1) and FGR (1–4 groups, with SR = 4) to assess SR and FGR effects on ecosystem N cycling and its response to elevated carbon dioxide (CO2) and N addition. We hypothesized that increased plant diversity (either SR or FGR) and elevated CO2 would enhance plant N pools because of greater plant N uptake, but decrease soil N cycling rates because of greater soil carbon inputs and microbial N immobilization. In partial support of these hypotheses, increasing SR or FGR (holding the other constant) enhanced total plant N pools and decreased soil nitrate pools, largely through higher root biomass, and increasing FGR strongly reduced mineralization rates, because of lower root N concentrations. In contrast, increasing SR (holding FGR constant and despite increasing total plant C and N pools) did not alter root N concentrations or net N mineralization rates. Elevated CO2 had minimal effects on plant and soil N metrics and their responses to plant diversity, whereas enriched N increased plant and soil N pools, but not soil N fluxes. These results show that functional diversity had additional effects on both plant N pools and rates of soil N cycling that were independent of those of species richness. |
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| Keywords: | CO2 elevation N enrichment net N mineralization plant diversity plant N pools soil inorganic N pools |
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