Resource-enhancing global changes shift soil multifunctionality towards faster cycling in arid grasslands

Soil multifunctionality in terrestrial ecosystems plays a pivotal role in providing sustainable services to humanity. Resource-enhancing global changes, such as increased precipitation and nitrogen (N) deposition can accelerate the transformation of various aspects of ecosystem functions from slow to fast cycling. The difference in how these global change factors influence soil multifunctionality in arid grasslands remains unknown, limiting our ability to manage these ecosystems under anthropogenic changes. Using a framework recently developed to quantify slow-to-fast cycling transitions in ecosystem functions, we tested the impact of increased precipitation and N addition on soil slow-fast multifunctionality and its components related to soil carbon (C), N, and phosphorous (P) functions by conducting two separate manipulative experiments in arid grasslands. Additionally, we explored the contribution of plant diversity, microbial diversity and soil properties to the variations of soil multifunctionality. We found that increased precipitation and N addition drove shifts in soil multifunctionality towards faster cycling. However, such shifts resulted from different responses of soil C, N and P functions. Specifically, increased precipitation resulted in faster C, N and P cycling functions, while N addition led to faster N cycling functions. Although above- and below-ground diversity and soil properties were closely linked to soil N and P functions, increased precipitation did not affect these abiotic and biotic drivers. Therefore, the impacts of increased precipitation on soil C, N and P functions were direct. In contrast, the impact of N addition on soil N functions was mediated through changes in above- and below-ground community composition and soil properties. Our results provide deeper insights into the driving mechanisms by which increased precipitation and N addition affect soil multifunctionality, indicating that the drivers of multifunctionality are context-dependent. Therefore, we should develop corresponding strategies to mitigate the impacts of different global change factors on soil multifunctionality in arid grasslands.