Contrasting wood carbon quality of angiosperms and gymnosperms drives fungal-mediated decomposition responses to nutrient enrichment

Abstract

Deadwood occupies about eight percent of the global forest carbon stock. Its high lignin content and low nutrient concentration typically inhibit microbial activity, yet the combined influence of these wood properties on fungi, the main decomposers of wood, has not been thoroughly explored. Here we tested how wood carbon quality (e.g., lignin carbon and cellulose carbon) and nutrient availability interactively shape fungal communities, microbial respiration, and decomposition rates of diverse angiosperm and gymnosperm trees under nitrogen (N; 100 kg N ha⁻¹ yr⁻¹), phosphorus (P; 15 kg P ha⁻¹ yr⁻¹), and combined N + P additions in a subtropical forest. Nutrient additions had opposing effects on fungal communities in angiosperms and gymnosperms and accelerated decomposition more in gymnosperms compared to angiosperms. Specifically, in relatively nutrient-rich, low lignin carbon of angiosperms, nutrient additions shifted fungal communities from Basidiomycota to Ascomycota dominance. This significantly increased fungal diversity, boosted the activities of hydrolytic carbon-acquiring enzymes, and enhanced cellulolytic carbon decomposition. In nutrient-poor, high lignin carbon of gymnosperms, nutrient additions strengthened Basidiomycota dominance, reduced fungal diversity, and promoted decomposition of lignin-derived carbon. Our study highlights that carbon quality mediates how nutrient additions accelerate wood decomposition by adjusting the dominant taxa of communities with decomposition traits adapted to target specific carbon compounds. It provides important information to forest managers aiming to boost forest carbon sequestration through selection of distinct tree species under global changes.