The effect of long-term controlled-release urea application on the relative abundances of plant growth-promoting microorganisms

Controlled-release urea (CRUs), including polymer-coated urea (PCU), sulfur-coated urea (SCU), and polymer/sulfur dual layer-coated urea (PSCU), have been demonstrated to increase crop yield and nitrogen use efficiency (NUE). However, the effects of long-term application of CRUs on soil microbial community and function remain unclear. In this study, a 12-year (2009–2021) 24-season wheat -maize rotation lysimeter experiment was studied to investigate the effects of PCU, SCU, and PSCU on soil microbial community composition and function. Wheat was grown, soil chemical properties were analyzed, and soil biological properties including enzyme activities and microbial community structure and function at the wheat filling stage were determined in 2021. The results showed that soil organic matter (SOM) contents were markedly increased by 3.1∼5.0% under the CRUs compared to conventional urea. Meanwhile, some carbon, nitrogen, and sulfur cycle enzyme activities, including cellulase (CE), urease and arylsulfatase (AS), were significantly enhanced by 23.4∼32.4%, 6.6∼32.1%, and 2.5∼3.7% under the CRUs compared to conventional urea, respectively. Redundancy analysis indicated that changes in bacterial and fungal communities were driven by SOM. Co-occurrence network analysis showed that wheat growth promotion by the CRUs was strongly linked to the high relative abundance (Z-score) of bacterial and fungal module 1, which included such plant growth-promoting microorganisms (PGPMs) as Arthrobacter, Bryobacter, Bradyrhizobium, Microscypha, and Marasmius. Compared with PCU, SCU and PSCU showed a better effect in increasing the relative abundances of PGPMs while inhibiting the growth of nitrobacteria, denitrifying bacteria, and plant pathogens, thereby better promoting wheat yields and reducing N loss and plant disease. Of the three CRUs, SCU and PSCU have significantly increased SOM, which provided sufficient substrate for the growth of PGPMs, thus increasing wheat yield. This study provides a support for long-term CRUs application and sustainable agriculture.