Soil microbial community composition and function are closely associated with soil organic matter chemistry along a latitudinal gradient

Despite the important roles of microorganisms in soil organic matter (SOM) decomposition and nutrient cycling, how their biomass, community composition and function are driven by a joint effect of edaphic and environmental factors at a large spatial scale remains unclear. Moreover, a mechanistic understanding of the associations among microbial communities and SOM chemistry as a key indicator of substrate availability over large spatial scales has been lacking until now. To fill this knowledge gap, we examined how soil microbial community abundance and composition (via phospholipid fatty acid (PLFA) analysis) and function (via enzyme activities and net N mineralization) were associated with the edaphic and environmental factors from six oriental oak (Quercus variabilis) forest sites arranged across a 11° latitudinal gradient in East China. We found strong relationships between SOM chemistry as indicated by ¹³C nuclear magnetic resonance (NMR) spectroscopy and microbial community composition and function along this gradient. For example, the ratio of fungi to bacteria (F/B) decreased with increasing carboxyl C percentage; the lower abundance of arbuscular mycorrhizal fungi (AMF) and decreased invertase activity in the southern sites were possibly related to higher ratio of alkyl to O alkyl (A/O); urease activity increased with carboxyl C percentage. Microbial biomass (total PLFAs) had positive relationships with urease activity, net N mineralization rate, and soil pH. Mean annual precipitation (MAP) and pH were important for overall microbial community composition. Overall, our results indicate that SOM chemistry is closely related to microbial community composition and function along the latitudinal gradient and should be considered in future studies. Our study contributes to a better prediction of microbial responses to possible substrate changes brought by future environmental changes, which is urgently needed under the context of accelerating global change.