Soil Biodiversity and Biogeochemical Cycles.

Soil food webs play a key role in the cycling of carbon (C) and nutrients and in sustainably provisioning ecosystem services. Despite the tremendous diversity of organisms that soil food webs harbor, we still know surprisingly little about the role of biodiversity in influencing ecosystem processes. With this study we aimed to test how a loss of soil foodweb diversity affects ecosystem processes, and under which circumstances loss of biodiversity matters most. We used meta-analysis to quantitatively assess how soil biodiversity affects soil C respiration, litter decomposition, and plant biomass production. We compared the response of process variables to changes in diversity both within and across groups of soil organisms that differed in body size, a grouping that typically correlates with ecological function. Plant biomass production was not affected by soil biodiversity. Plant tissue decomposition was reduced by 18% when studies that manipulated both within- and across-body size group diversity were included in the meta-analysis, or by 37% following a loss of soil fauna diversity. Soil C respiration was reduced by 27.5% upon a loss of both within- and across-body size group diversity, or with a loss of microbial diversity (-41%). Taken together, our findings show that loss of soil biodiversity can strongly impact ecosystem processes, and highlight the importance of diversity across groups of organisms (e.g., primary consumers and secondary decomposers) for maintaining full functionality of ecosystem processes. However, methodological concerns associated with studies aiming to link soil biodiversity and ecosystem function can lead to significant over- or underestimation of soil biodiversity effects on ecosystem processes, challenging extrapolation to natural field settings. Increased research emphasis on manipulating diversity across levels of functional trait diversity is critical for enhancing our understanding of the role of soil food web diversity in driving ecosystem services.