Resource limitation and modeled microbial metabolism along an elevation gradient

Abstract Soil microbes have a great influence on the feedbacks of carbon (C)-climate, and their metabolic activities are limited by resource availability. Altitudinal gradients strongly affect soil microbial communities, but the effects on microbial resource limitation and their regulation for C dynamics remain unclear. In this study, we designed an altitudinal gradient experiment that included six altitudinal sites from 1308 m to 2600 m in the Qinling Mountains, China. The enzymatic stoichiometry was determined and modeled to investigate microbial resource limitations and major microbial metabolism processes (e.g., organic C decomposition rate and microbial respiration rate) along the elevation gradient. Other environmental variables including mean annual temperature (MAT) and mean annual precipitation (MAP), the C: nitrogen (N): phosphorus (P) ratio in soil total nutrients, available nutrients, and microbial biomass were also measured. The results showed that soil microbes suffered from N limitation in our study and microbial N limitation significantly increased with increasing elevation. But the rates of both organic C decomposition and microbial respiration greatly decreased with increased elevation. These trends suggest that warming induced by elevation change might relieve N limitation for microbes and lead to increased soil C release. Redundancy analysis (RDA) showed that MAT and soil nutrient stoichiometry, particularly for the DOC: TDN ratio, explained more variations for changes in microbial N limitation and major microbial processes. Collectively, our study demonstrated that the higher microbial N limitation at high elevation may be beneficial to soil carbon accumulation by changing the C: N ratio, which provided insights into microbially mediated soil carbon release under global warming.