Different roles of core and noncore bacterial taxa in maintaining soil multinutrient cycling and microbial network stability in arid fertigation agroecosystems

Microbes play an essential role in soil biogeochemical processes and maintenance of soil nutrients, but not all microbial taxa contribute equally, and their functions in soil nutrient cycling and microbial network stability are unclear in arid fertigation agricultural ecosystems. In this study, a 4-year field experiment was conducted in an irrigation district in China using three levels of irrigation [high (400 mm), medium (300 mm) and low (200 mm)] and two levels of fertilization [high (600 kg/ha P2O5 + 300 kg/ha urea) and low (300 kg/ha P2O5 + 150 kg/ha urea)] to reveal the ecological roles of core and noncore taxa in maintaining soil nutrient cycling and their associations with microbial network stability. Our results showed that combining medium irrigation with low fertilization resulted in higher levels of soil organic C, inorganic N, available P, multinutrient cycling and noncore bacterial diversity compared with the other treatments. Soils supporting a higher diversity of noncore bacterial taxa had a high soil multinutrient cycling index, while soils harbouring highly diverse core taxa exhibited a more stable bacterial network. The soil multinutrient cycling index was also significantly positively related to the subnetwork modularity of noncore taxa. Moreover, noncore taxa could serve as diverse pools that turn into core taxa in response to changes in the external environment. Acinetobacter, Flavobacterium, Gemmatimonas and Salinimicrobium, which belong to the noncore taxa, were involved in soil C and N cycling in the arid agricultural ecosystem. Synthesis and applications. Our results suggest that soil microbiota contribute differently to ecosystem functions. Changes in soil nutrient cycling were more closely related to variations in noncore taxa, while bacterial network stability was more associated with core taxa. Our study emphasized the role of noncore microbiota, which has been neglected in previous studies. Furthermore, our findings suggested that combining medium irrigation with low fertilization is effective for enhancing soil nutrients and bacterial diversity, providing guidance for managing arid agricultural ecosystems.