Plant functional traits predict soil multifunctionality under increased precipitation and nitrogen addition in a desert steppe

Soil multiple functions (soil multifunctionality, SMF) are crucial in regulating biogeochemical cycling in grassland ecosystems. Global changes (e. g. increased precipitation and nitrogen deposition) are strongly affecting SMF in arid grasslands. However, little is known about how increased precipitation, nitrogen deposition and their combinations affect SMF in desert steppe. Here, we conducted a 6-year manipulated experiment to investigate the effects of increased precipitation, nitrogen addition and their interactions on aboveground biomass, species diversity, functional traits, soil properties and different aspects of SMF. Linear mixed models were used to explore the relationships between these biotic and abiotic factors we considered and soil nutrient pools (SMF-Nutrient pool), soil enzyme activities (SMF- Nutrient turnover) and SMF under increased precipitation and nitrogen addition. We found that increased precipitation increased leaf thickness and soil moisture but decreased leaf nitrogen content. Nitrogen addition increased leaf thickness and leaf nitrogen content but decreased soil pH. Increased precipitation increased SMF and SMF- Nutrient turnover, and nitrogen addition increased SMF and SMF-Nutrient pool. Further, the interaction between increased precipitation and nitrogen addition increased SMF and SMF-Nutrient pool. Results of linear mixed models showed that SMF was positively associated with leaf nitrogen content and specific leaf area. SMF-Nutrient pool was positively related to leaf nitrogen content but negatively related to aboveground biomass. SMF-Nutrient turnover showed positive relationships with specific leaf area, plant height and soil moisture. Our results suggest that increased precipitation, nitrogen addition and their interactions can enhance soil multifunctionality by increasing soil nutrient pools and nutrient turnover. Plant functional traits can predict the changes in soil functions under increased precipitation and nitrogen addition. These findings highlight the importance of considering different aspects of soil functions in response to global changes and the role of plant functional traits in predicting soil functions under global changes.