Cascade effects of forest thinning on microbial composition and function of various tree species and multiple decomposition time series: Insights from deadwood decomposition in tropical forests

Abstract

Deadwood-inhabiting bacteria and fungi were crucial in understanding ecosystem functioning in carbon turnover. The objectives of this study were to investigate microbial succession in deadwood and analyze bacterial-fungal ratio, composition, and diversity of various tree species; it explored fungal traits during decomposition and uncovered unique bacterial-fungal networks; thinning effects on microbial composition over three years and the roles of nitrogen cycle in energy metabolism were assessed; the analysis included carbohydrate-active enzyme gene families, examining bacterial and fungal contributions to organic compound degradation; the impacts of thinning degrees on specific carbohydrate-active enzyme gene families were also evaluated. Deadwood samples of Machilus thunbergii and Quercus pachyloma in decomposition time series spanning 2017, 2018, and 2019 under thinning degrees of 0%, 20%, 40%, 60%, and 80% were analyzed using metagenomics. The results reflected the decomposition stages of deadwood with changes in microbial composition and function over time. Furthermore, this study revealed the dominance of microbial groups, including Proteobacteria and Actinobacteria for bacteria and Ascomycota and Basidiomycota for fungi. This study revealed the prevalence of wood saprotrophs and mycoparasites. Deadwood of Machilus thunbergii fostered more microbial networks with mutualistic relationships, while Quercus pachyloma encouraged more microbial networks with antagonistic interactions. The sensitivity of microbial composition to thinning degrees was primarily evident at lower taxonomic levels (such as family to species). Furthermore, nitrogen cycle genes and carbohydrate-active enzyme gene families unveiled the roles of bacteria and fungi, including nitrogen fixation and lignin degradation. Thinning significantly impacted the gene families of carbohydrate-active enzymes, especially in the second year, influencing the microbial resource requirements and metabolic function in deadwood decomposition. In conclusion, the findings provided insights into the intricate microbial dynamics and their ecological implications in tropical forests. Lastly, this study underscored the importance of actively managing sustainable forests to promote desired microbial roles, thus enhancing ecosystem functioning.