Abstract
Subsoil microbiomes play important roles in soil carbon and nutrient cycling, yet our understanding of the controls on subsoil microbial communities is limited. Here, we investigated the direct (mean annual temperature and precipitation) and indirect (soil chemistry) effects of climate on microbiome composition and extracellular enzyme activity throughout the soil profile across two elevation-bioclimatic gradients in central California, USA. We found that microbiome composition changes and activity decreases with depth. Across these sites, the direct influence of climate on microbiome composition and activity was relatively lower at depth. Furthermore, we found that certain microbial taxa change in relative abundance over large temperature and precipitation gradients only in specific soil horizons, highlighting the depth dependence of the climatic controls on microbiome composition. Our finding that the direct impacts of climate are muted at depth suggests that deep soil microbiomes may lag in their acclimation to new temperatures with a changing climate.
Highlights
Microbial community composition varies considerably throughout the soil profile [1] likely due to edaphic factors that change with depth, including organic carbon (C) availability, nutrients, pH, and texture [2,3,4,5]
While the variation in the microbial community explained by horizon was overall lower than site identity, master horizon consistently explained a greater amount of the variation in microbial community composition than depth (Table 1)
We find that certain microbial taxa change in relative abundance over large temperature and precipitation gradients only in specific soil horizons, highlighting the depth dependence of the climatic controls on microbial community composition
Summary
Microbial community composition varies considerably throughout the soil profile [1] likely due to edaphic factors that change with depth, including organic carbon (C) availability, nutrients, pH, and texture [2,3,4,5]. Most studies on subsoil microbial communities do not span large ecological gradients, preventing a conclusive understanding of large-scale drivers of subsoil microbial communities. Across broad ecological gradients, our understanding of the controls of subsoil microbial communities is inconclusive for bacteria [1] and even more limited for fungi. Climate is often considered a major driver of microbial community composition and activity at large spatial scales in the surface soil [6,7,8]. The role of climate in predicting subsoil microbial community composition and activity is still unclear. Given that subsoil microbial communities play a significant role in decomposing the ~1400 Pg of soil organic carbon (SOC) stored below 20 cm [9], understanding the large-scale controls over subsoil microbial communities is critical in predicting future soil C stocks and future temperatures
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