Tree species diversity modulates the effects of fungal pathogens on litter decomposition: evidences from an incubation experiment

Litter decomposition is a major determinant of carbon (C) and nutrient cycling in ecosystems, and contributes to soil organic carbon (SOC) formation. Ongoing global changes are exacerbating biodiversity loss, potentially elevating foliar fungal pathogen infections and consequently impacting litter quality and quantity. However, the potential interplay between biodiversity loss and fungal pathogen infection on litter decomposition and SOC formation remains largely unknown. We collected leaf litter with different fungal pathogen infection levels across various tree species richness (TSR) stands within a subtropical forest biodiversity-ecosystem functioning experiment in China. We conducted a 383-day incubation experiment using these litter samples and measured initial litter quality, litter mass loss, and incubation-induced changes in mineral-associated soil C and nitrogen (N). We found that litter from higher richness plots exhibited lower N concentration and higher carbon to nitrogen ratio (C:N). Moreover, TSR exerted control over the effects of fungal pathogen infection on litter quality, decomposition, and N turnover. Under higher richness, litter with higher fungal infection levels tended to have higher N concentration and lower C:N, thus leading to faster decomposition rates and more soil N loss. Meanwhile, litter with elevated fungal infection levels contributed more to litter C retained in soil. Our findings indicate that changes in litter chemistry and fungal pathogen infection rates induced by biodiversity loss could affect decomposition and the extent of C stabilized in soil, highlighting the significance of considering fungal pathogen infection in studies related to biodiversity and biogeochemical cycles.