Five years nitrogen reduction management shifted soil bacterial community structure and function in high-yielding ‘super’ rice cultivation

Integrated nitrogen (N) management has been adopted for the cultivation of ‘super’ rice to achieve high yield while minimizing environmental risks. How soil microbial communities respond to integrated N management in ‘super’ rice production remains unclear. Five years of field experiment was conducted under a wheat–rice system, with four treatments: conventional farming practices (300 kg ha^–1 N), reduced (270 kg ha^–1) and increase N (360 kg ha^–1) application coupled with increased planting density and accurate irrigation, and a non-N control. The results showed that after five years of treatment, the predominant bacterial phyla shifted from Proteobacteria (22.99%), Acidobacteria (17.04%), and Chloroflexi (14.43%), to Proteobacteria (30.83%), Chloroflexi (20.9%), and Actinobacteria (16.07%). The structure of soil bacterial community differed among the treatments, with available phosphorus contents and pH as key drivers in the first year and NO₃^--N content in the fifth year. The highest soil N content was detected in the treatment with increased N application, whereas the reduction of N application led to a 32% decrease in soil NO₃^–-N content. A greater difference was detected in N functional groups in the fifth year than the first year. Following reduced N application, there was also an increased proportion of N-transforming groups, including those involved in aerobic ammonia oxidation, aerobic nitrate oxidation, nitrate denitrification, and nitrite denitrification. Collectively, N fertilizer reduction coupled with accurate irrigation was most effective in regulating soil bacterial communities, especially those associated with N transformation in ‘super’ rice cultivation.