pH-Driven Modulation of Microbial Community Structure and Functional Succession in Fallen Oak Logs

Deadwood serves as a vital carbon sink in forest ecosystems, fostering diverse microbial communities. pH shapes microbial community structure and metabolism in deadwood, especially in mid-to-late decomposition stages with strong pH gradients. In fallen Quercus liaotungensis logs, the variation in pH was closely related to changes in available nutrients and the activity of lignocellulolytic enzymes, particularly involved in cellulose degradation. These changes reflect a successional transition in microbial community structure and function, as revealed by ITS and 16S rRNA amplicon sequencing. Specifically, low pH (< 4.5) suppressed lignocellulosic enzyme activity but showed higher microbial diversity and greater modularity in fungal-bacterial co-occurrence networks, while bacterial communities also exhibited niche differentiation, suggesting distinct ecological strategies employed by fungi and bacteria in response to pH changes. Moreover, the abundance of major functional fungal groups and specific bacterial functional taxa varied with pH. Co-occurrence network analysis identified the bacterial order Micrococcales as a core taxonomic group associated with high-pH environments. This study elucidates how pH regulates microbial nutrient utilisation in a self-contained decomposing system and provides a basis for understanding how pH-driven microbial metabolic adjustment promotes nutrient transformation during deadwood decomposition.