Global change factors cause decoupling of nutrient dynamics and asynchrony between microbial communities and ecological functions in a temperate grassland soil

Soil microbial communities and grassland ecosystem processes are increasingly confronted with multiple global change factors (GCFs). There is still a lack of research on how these multiple GCFs interact and impact soil microbial communities and their functions. To address this gap, we conducted a simulation experiment to examine the individual and interactive effects of the four most critical and prevalent GCFs, elevated carbon dioxide concentration (eCO₂), elevated temperature (eT), decreased precipitation (dP), and elevated nitrogen (N) deposition (eN). This study focused on their effects on soil physicochemical properties, bacterial and fungal communities, and extracellular enzyme activities (EEAs) related to carbon (C), N, and phosphorus (P) cycles in a temperate grassland. Results showed that eCO₂, eN, and dP tended to increase EEAs, while having neutral effects on microbial diversity and community composition. On the other hand, eT resulted in decreases in soil pH, total C, total N, EEAs, and microbial diversity, but increases in plant biomass, total P, microbial richness, and network complexity and stability. This shift in the nutrient limitation from P to N under warming conditions resulted in decoupling of nutrients. Neutral or slightly negative relationships were found between enzyme activities and microbial richness, diversity, and dominant species, and the responses of microbial communities and ecological functions were asynchronous under GCFs. Importantly, our results revealed significant higher-order interactions among GCFs and found that they had notable effects on soil physicochemical properties as well as on microbial communities and ecological functions. These findings provide valuable insights and suggestions for ecological adaptations to future global changes.