Linking leaf‒litter‒soil stoichiometry to microbial carbon‒use efficiency across different forest types in north subtropical China

Abstract

Changes in forest type influence microbial nutrient use efficiency, yet few studies have examined how the ecological stoichiometric characteristics of leaves, litter, and soil affect microbial carbon use efficiency (CUE) across different forest types. This study examines how forest type and soil depth influence nutrient dynamics, microbial resource limitation, and microbial CUE in three representative forest types—pure Pinus massoniana (PM), pure Quercus acutissima (QA), and mixed Pinus massoniana–Quercus acutissima (PM-QA)—in northern subtropical China. Soil samples were collected from two depths (0–5 cm and 5–30 cm) across 15 forest plots. Results showed significant differences in nutrient content and stoichiometric ratios among forest types. QA exhibited the highest carbon (C), nitrogen (N), and phosphorus (P) contents in soil, while PM had the highest leaf and litter C:N ratio and soil N:P ratio. Litter C content, microbial biomass carbon (MBC) and the microbial biomass C:N ratio were highest in PM-QA, contributing to the greatest microbial CUE, whereas PM had the lowest microbial CUE and the strongest nitrogen limitation. The microbial CUE of PM-QA (0.43) was 34 % higher than PM (0.32) and 14 % higher than QA (0.38), indicating improved microbial efficiency in mixed forests. Microbial resource limitation patterns revealed co-limitation by N and P, with PM experiencing the strongest P limitation. Correlation analyses showed that microbial CUE was positively associated with microbial biomass C:N ratio and vector angle but negatively correlated with soil total nitrogen (TN), soil N:P ratio, and enzyme C:N ratio. These findings highlight the role of forest type in shaping soil microbial function, with mixed forests enhancing nutrient availability, reducing resource limitation, and improving microbial CUE, ultimately contributing to soil C sequestration. This study provides new insights into how forest composition regulates microbial function and nutrient cycling, with implications for sustainable forest management.