Soil abiotic properties and plant functional diversity co-regulate the impacts of nitrogen addition on ecosystem multifunctionality in an alpine meadow.

Soil abiotic properties and plant diversity have been shown to affect ecosystem functions in alpine meadow ecosystems. However, we know little about the relative importance of these factors in driving the responses of multiple ecosystem functions simultaneously (multifunctionality) to nitrogen (N) enrichment. Here, we measured soil abiotic properties (soil pH; available nitrogen, AN; available phosphorous, AP; and dissolved organic carbon, DOC) and multiple plant diversity metrics (species diversity, SD; functional diversity, FD; and phylogenetic diversity, PD) after a 5-year N fertilization experiment (0, 5, 10, and 15 g N m-2 yr-1) to evaluate their roles in mediating the impacts of N addition on aboveground plant functions (APF), soil microbial functions (SMF), and ecosystem multifunctionality (EMF) in a N-limited Tibetan alpine meadow. We found that N addition decreased APF but increased SMF and EMF. Structural equation models (SEMs) showed that APF was co-driven by soil DOC and the community weighted mean for plant traits (CWMs), and SMF was driven by soil DOC, soil AN, CWMs and functional dispersion (FDis). The effects of N addition on EMF were driven by soil AN and FDis. Our results suggest that the effects of N enrichment on APF, SMF, and EMF are driven by differential mechanisms. Furthermore, the findings suggest that FD is superior to SD and PD in mediating the responses of ecosystem functions to N enrichment.