Impact of plant litter decomposition on soil microbial diversity and ecosystem multifunctionality

Soil microbial communities play a key role in maintaining ecosystem services and agricultural sustainability. However, experimental evidence linking microbial diversity to soil multifunctionality in agroecosystems remains limited. In this study, we conducted a controlled indoor litter decomposition experiment using citrus leaves, alfalfa leaves, and their mixture, to investigate the coupling mechanism between soil bacterial/fungal diversity and soil ecosystem multifunctionality. Our results showed that litter addition had a stronger influence on fungal diversity than on bacterial diversity. Alfalfa litter significantly increased fungal diversity, while citrus leaves reduced bacterial diversity, likely due to their high content of aromatic volatile organic compounds (VOCs). The mixture of both litters enhanced the diversity of both bacterial and fungal communities. Litter decomposition also reshaped microbial community structures, particularly among fungi, and primarily affected rare taxa rather than dominant ones. Importantly, soil fungal diversity was positively associated with enhanced soil multifunctionality, whereas bacterial diversity exhibited a negative correlation. These findings demonstrate that different litter types exert contrasting effects on microbial communities and their ecological functions. The results highlight that alfalfa litter improves soil multifunctionality mainly through increased fungal diversity and nutrient turnover, while citrus leaf VOCs potentially hinder bacterial activity, leading to reduced soil functional outcomes. • Soil bacterial and fungal communities exhibited distinct patterns of variation. • Plant litter addition significantly increased soil fungal diversity. • Enhanced fungal diversity contributed to improved soil multifunctionality. • Rare microbial taxa were more sensitive to plant litter decomposition. • Volatile organic compounds (VOCs) from citrus leaves may regulate the decline in bacterial diversity.