Latitudinal patterns and drivers of plant lignin and microbial necromass accumulation in forest soils: Disentangling microbial and abiotic controls

Plant- and microbial -derived compounds are the two primary sources of the soil organic carbon (SOC) pool. However, whether and how biotic and abiotic factors regulate the means through which microbes and plants contribute to SOC accumulation at a regional scale remains unclear. This study investigated the distribution patterns of plant lignin components and microbial necromass in soils, as indicated by lignin phenols and amino sugars across five latitudinal forests in eastern China. The contents of plant lignin and microbial necromass in the soil increased with increasing latitude. However, their contributions to SOC followed quadratic patterns with increasing latitude. Given its positive relationship with SOC content in all examined forests, microbial necromass seemed to play a more critical role in SOC accumulation than lignin phenols. Moreover, plant lignin and microbial necromass accumulation and their contributions to SOC were mainly influenced by the joint effects of climatic variables, microbial traits, and soil properties, but their importance was divergent. Specifically, the mean annual temperature (MAT) and soil phosphorus content were central to plant lignin accumulation, whereas MAT and the microbial richness: biomass ratio mainly controlled microbial necromass accumulation. These findings demonstrate that microbial necromass plays a more critical role than plant lignin in forest SOC accumulation and further highlight the importance of microbial traits in microbial necromass accumulation.