The paper by Schimel and Schaeffer explores the role of microbial communities in carbon (C) cycling in soil. It discusses how the composition of microbial communities affects biogeochemical processes at the ecosystem scale, focusing on the phylogenetic level at which microbes form meaningful guilds based on life history strategies. The authors argue that while microbial community structure may influence the rate of organic matter (OM) breakdown in the rhizosphere and detritus, it is likely less important in mineral soils, where physical access to occluded or sorbed substrates is the rate-limiting factor. They highlight the importance of how microbes allocate carbon, as this can affect soil structure and function, and the long-term fate of C in soil. The paper also reviews the causes and nature of microbial diversity in soil, emphasizing the role of niche and functional differentiation in explaining patterns of diversity. Finally, it discusses the consequences of soil community composition on C cycling, including the importance of extracellular enzymes, extracellular polysaccharides, cell wall polymers, and stress response compounds produced by microbes. The authors conclude that the influence of microbial community composition on C cycling is associated with deep evolutionary divergences and that the specific compounds produced by microbes likely affect soil processes most strongly at the shortest or longest time scales, while less so at the interannual "ecosystem" scale.The paper by Schimel and Schaeffer explores the role of microbial communities in carbon (C) cycling in soil. It discusses how the composition of microbial communities affects biogeochemical processes at the ecosystem scale, focusing on the phylogenetic level at which microbes form meaningful guilds based on life history strategies. The authors argue that while microbial community structure may influence the rate of organic matter (OM) breakdown in the rhizosphere and detritus, it is likely less important in mineral soils, where physical access to occluded or sorbed substrates is the rate-limiting factor. They highlight the importance of how microbes allocate carbon, as this can affect soil structure and function, and the long-term fate of C in soil. The paper also reviews the causes and nature of microbial diversity in soil, emphasizing the role of niche and functional differentiation in explaining patterns of diversity. Finally, it discusses the consequences of soil community composition on C cycling, including the importance of extracellular enzymes, extracellular polysaccharides, cell wall polymers, and stress response compounds produced by microbes. The authors conclude that the influence of microbial community composition on C cycling is associated with deep evolutionary divergences and that the specific compounds produced by microbes likely affect soil processes most strongly at the shortest or longest time scales, while less so at the interannual "ecosystem" scale.