Identify the key factors driving the lignocellulose degradation of litter along a forest succession chronosequence from the perspective of functional genes

The purpose of this paper was to discover the key factors driving the lignocellulose degradation in litter along a forest succession chronosequence from the perspective of functional genes. We investigated four natural successive stages of forests (white birch forest, broad-leaved mixed forest, coniferous-broad-leaved mixed forest, and mixed broadleaved-Korean pine forest). We determined the lignocellulose degradation of litter and the absolute abundance of related functional genes by using high-throughput-qPCR. There was strong degradation of cellulose content, hemicellulose and lignin contents in the litter decomposition layer in the early and late stages of forest succession, respectively. Furthermore, forest succession changed microbial communities' succession and increased fungal Shannon diversity, and then enhanced the absolute abundance of lignocellulose-degrading genes and nitrogen-cycling genes. By network analysis, bacterial and fungal module 1 were key modules for producing lignocellulose-degrading genes and nitrogen cycling genes, while fungal module 2 was a key module for lignin-degrading genes. Fungi were strongly correlated with functional genes based on Procrustes analysis. Additionally, cellulose-degrading genes were the key factor driving the cellulose degradation in the early period of forest succession, while fungal diversity and composition were key drivers in promoting the degradation of lignin in the late period of forest succession. Our study provided insight into the mechanisms underlying the soil microbe-driven functional changes in nutrient cycling and an understanding of the decomposition kinetics of litter at a more microscopic level in the process of forest succession.