Land use intensity constrains the positive relationship between soil microbial diversity and multifunctionality

Aims: The positive soil biodiversity and multifunctionality relationship has been widely recognized, however in agricultural ecosystems, this relationship is context dependent and could be altered by land use intensity (LUI). Understanding how LUI affects soil microbial community and multifunctionality (SMF) is instructive for optimizing external inputs and managements. Methods: We sampled soils from three cropping systems (cotton, wheat-maize and vegetable) with different LUI, sequenced both bacterial and fungal communities, and quantified the multifunctionality by averaging carbon, nitrogen and phosphorus cycling functions. The relationship between soil microbial diversity and SMF was further explored. Results: The results showed that the positive effects of soil microbial diversity on SMF was significantly affected by LUI. In general, LUI decreased SMF and both bacterial and fungal diversity. Cotton and wheat-maize rotation systems with relatively lower LUI showed higher microbial diversity and SMF compared with the vegetable system, which had the highest LUI and the lowest SMF. Moreover, bacterial but not fungal diversity drove this positive relationship between microbial diversity and SMF in both cotton and wheat-maize systems but not in the vegetable system, indicating a larger bacterial effect in lower LUI system. Random forest and structural equation modeling further confirmed bacterial diversity and composition contributed to SMF mainly via promoting carbon and phosphorus cycling. Conclusions: Our findings highlight the importance of LUI in influencing the relationships of biodiversity-SMF and further demonstrate that soil microbial diversity conservation with less anthropogenic disturbances is important for supporting soil functioning in agroecosystems.