Decaying logs and gap positions jointly mediate the structure and function of soil bacterial community in the forest ecosystem

Abstract

Altres ajuts: the Fundación Ramón Areces Project CIVP20A6621.Soil bacteria play a vital role in soil processes within forest ecosystems, yet the changes in the structure and function of soil bacterial communities with decaying logs and forest gaps remain inadequately understood. To address this knowledge gap, we conducted an experiment involving the incubation of five decay classes (I-V, at increasing levels of decay) of Minjiang fir (Abies faxoniana) logs at forest gap center, gap edge and closed canopy areas in a subalpine forest on the eastern Tibetan Plateau, China. We employed high-throughput sequencing (Illumina Novaseq) and Functional Annotation of Prokaryotic Taxa (FAPROTAX) to analyze the diversity, composition and function of soil bacterial communities beneath decaying logs. A total of 11,291 operational taxonomic units were observed. After six years, soil bacterial diversity, composition and function exhibited significant variations across log decay classes and gap positions. Soil bacterial alpha diversity beneath decaying logs was significantly higher and lower in decay classes III/IV and I, respectively, and significantly higher under the center/edge of forest gaps than closed canopy. Additionally, Proteobacteria, Acidobacteria, and Actinobacteria were the dominant bacterial phyla, regardless of decay classes and gap positions. The relative abundance of most soil bacterial genera varied significantly with decay classes and gap positions. Results from FAPROTAX analysis showed that chemoheterotrophy and aerobic chemoheterotrophy were the dominat functional groups across all samples. Moreover, functional groups associated with soil carbon cycle showed higher abundance beneath highly decayed logs (IV-V), and functional bacteria participating in the nitrogen and sulfur cycles were enriched in the gap center, underscoring the importance of decaying logs and forest gaps in the succession of soil bacterial communities. Overall, the structure and function of soil bacterial communities showed significant variation depending on the log decay stage, e.g., decay class, with these dynamics being strongly influenced by forest gap positions. Thus, maintaining woody debris in the middle (III) to late (IV) stage of decay in the forest floor, particularly in the center of forest gaps, is beneficial for sustaining soil bacterial biodiversity in forest ecosystems. These results provide insights into managing woody debris for a sustainable forest practice