Log decomposition and forest gaps synergistically shape the structure and function of wood-inhabiting microbial communities in forest ecosystems

Abstract

Understanding the intricate relationships between microbes, log decomposition, and forest disturbance is vital for conserving microbial diversity and maintaining the health of forest ecosystems. However, the successional dynamics of wood-inhabiting microbial communities across different decay stages and their responses to varying forest gap positions remain poorly understood. Here, we present results from a 6-year in-situ experiment using Minjiang fir (Abies faxoniana) logs across five decay classes (I–V, representing increasing levels of decay) placed in gap centers, gap edges and under a closed canopy on the eastern Tibetan Plateau, China. Using high-throughput sequencing coupled with FUNGuild and Functional Annotation of Prokaryotic Taxa (FAPROTAX) analyses, we identified a total of 6193 fungal and 10,530 bacterial operational taxonomic units (OTUs). Fungal diversity in decaying logs initially increased, peaking in class III (maximum increase: 64 %), before declining in later stages. In contrast, bacterial diversity increased continuously, reaching its highest levels in decay classes IV and V (maximum increase: 27 %). Both fungal and bacterial species richness in decaying logs were greater at the center of forest gaps than under the closed canopy. Highly decayed logs favored specific fungal functional groups, such as ectomycorrhizal and saprotrophic fungi. Bacterial functional groups associated with the carbon cycle peaked in highly decayed logs (class V), whereas those linked to the nitrogen cycle were more abundant under the closed canopy. The dominant phyla, genera, and functional groups of fungi and bacteria were primarily driven by changes in log water content mediated by forest gaps, and the resulting pH and nutrient dynamics, rather than by temperature. These results highlight the pivotal roles of decaying logs and forest gaps in shaping the structural and functional succession of microbial communities. Therefore, maintaining coarse woody debris across various decomposition stages, particularly advanced decay classes, along with moderate gap disturbance, promotes the conservation of wood-inhabiting microbial diversity in forest ecosystems. Our study provides in-depth insights into the positive effects of forest disturbances, which are essential for informing sustainable forest management practices and preserving ecosystem health.