Conservation tillage and moderate nitrogen application changed the composition, assembly pattern and interaction network of abundant and rare microbial community on straw surface

Microbial-driven straw decomposition is important for soil organic carbon accumulation, nutrient uptake, and crop utilization. However, the mechanism by which tillage and fertilization interactions form the abundant and rare microbial communities that mediate straw degradation in dry farmland remains unclear. Based on an interaction experiment between three tillage practices (zero-till, chisel-till, and conventional plow-till) and three levels of nitrogen fertilizer (180, 240, and 300 kg·N·ha−1), we aimed to understand the community assembly process of abundant and rare microbe in the decomposition of maize straw. We found that the abundant bacterial and fungal communities were governed by stochastic processes, whereas the rare bacterial communities were dominated by deterministic processes. Furthermore, the relative importance of deterministic assembly of all microbial communities was higher in conservation tillage; in addition, the deterministic assembly process of the abundant bacterial and fungal communities was significantly increased by the medium level of nitrogen fertilizer (240 kg·N·ha−1), but the rare microbial community was not significantly affected. Redundancy analysis (RDA) and threshold indicator taxa analysis (TITAN) indicated that soil temperature, pH, and NO3− are the key influencing factors for the abundant and rare microbial communities. Overall, conservation tillage and a medium level of nitrogen fertilizer (240 kg·ha−1) in dry farmland promoted straw decomposition by regulating the development and turnover of straw-decomposing communities, in which they regulated bacterial community succession rather than fungi within a short decomposition time. These findings highlight the distinct responses to conservation tillage and N fertilization in the community assembly of abundant and rare biospheres in maize straw decomposition, and provide additional evidence for the development of conservation tillage applications in drylands.