Nutrient enrichment shapes litter micro-food webs in a subtropical plantation

Tropical and subtropical forests are important for terrestrial gross primary production. These forests are limited by nutrient availability and are vulnerable to nutrient enrichment under global change. However, little is known about how and why belowground biodiversity responds to nutrient enrichment during litter decomposition in these forests – the fundamental process fuelling nutrients to the soil system while supporting carbon sequestration. We conducted a 6-year field microcosm experiment and used a linear mixed effect to investigate the effects of nutrient enrichment on micro-food webs (i.e., microbes and nematodes) of leaf and root litters in a subtropical plantation. We found strong effects of nutrient enrichment on diversity and structure of microbes and nematodes during litter decomposition. For instance, fertilization (nitrogen+phosphorus; N + P) significantly decreased fungal richness of diversity (OTUs richness) throughout the decomposition process, and shifted the litter biota toward lower bacterial evenness of diversity (OTUs evenness), with higher relative abundances of fungi and herbivores at the humus-near stage. Nutrient enrichment also modulated leaf and root litter micro-food webs in different ways. NP addition had stronger positive effects on leaf litter bacterial oligotrophs:copiotrophs at the early stage, and stronger positive effects on root litter fungi:bacteria, but stronger negative effects on leaf litter fungal oligotrophs:copiotrophs at the humus-near stage. Overall, our results indicate that nutrient enrichment significantly alters microbes and microfauna associated with litter decomposition in subtropical forests, with important consequences for nutrient replenishment and soil organic carbon formation.