Microbial control over carbon cycling in soil

TLDR

Terrestrial microbial ecology seeks to link community composition to ecosystem‑scale biogeochemical processes, yet evidence for such influence on broad soil carbon cycling—especially in mineral soils where substrate access limits decomposition—is limited, with microbial effects largely mediated by carbon allocation and extracellular enzymes. The study aims to determine how soil microbial community structure and carbon allocation influence carbon cycling and long‑term sequestration in soils. The authors analyze microbial guilds defined by phylogeny and life‑history strategies, assessing when community differences can alter organic‑matter breakdown, concluding that such effects are significant in rhizosphere and detritus but negligible in mineral soil. They find that microbial community structure influences organic‑matter decomposition in the rhizosphere and detritus but has little impact on mineral‑soil carbon turnover.

Abstract

A major thrust of terrestrial microbial ecology is focused on understanding when and how the composition of the microbial community affects the functioning of biogeochemical processes at the ecosystem scale (meters-to-kilometers and days-to-years). While research has demonstrated these linkages for physiologically and phylogenetically "narrow" processes such as trace gas emissions and nitrification, there is less conclusive evidence that microbial community composition influences the "broad" processes of decomposition and organic matter turnover in soil. In this paper, we consider how soil microbial community structure influences C-cycling. We consider the phylogenetic level at which microbes form meaningful guilds, based on overall life history strategies, and suggest that these are associated with deep evolutionary divergences, while much of the species-level diversity probably reflects functional redundancy. We then consider under what conditions it is possible for differences among microbes to affect process dynamics, and argue that while microbial community structure may be important in the rate of OM breakdown in the rhizosphere and in detritus, it is likely not important in the mineral soil. In mineral soil, physical access to occluded or sorbed substrates is the rate-limiting process. Microbial community influences on OM turnover in mineral soils are based on how organisms allocate the C they take up—not only do the fates of the molecules differ, but they can affect the soil system differently as well. For example, extracellular enzymes and extracellular polysaccharides can be key controls on soil structure and function. How microbes allocate C may also be particularly important for understanding the long-term fate of C in soil—is it sequestered or not?