Differential Responses of Microbial Network Stability to Post-Tobacco Crop Rotation Driven by Contrasting Soil Nutrient Conditions

Background Continuous monocropping of flue-cured tobacco disrupts soil nutrient balance and degrades microbial communities, whereas post-tobacco minor crop rotations alleviate these constraints. Methods Tobacco fields in Geyi and Xize, Xuanwei City, Yunnan Province, were used to compare six rotation treatments with leguminous and non-leguminous crops to clarify the effects of post-tobacco rotation on soil nutrients and microbial communities in the nutrient-rich Geyi and nutrient-poor Xize regions. Results Intercropping with legumes better retained available nutrients in both regions. Bacterial communities showed greater sensitivity to post-tobacco rotation management than fungal communities, as evidenced by greater variation in bacterial α-diversity, higher explanatory rates of bacterial PCoA ordination axes (56.6% and 50.4% in Geyi and Xize, respectively; 31.6% and 36.8% for fungi), and bacterial community assembly being mainly governed by deterministic processes (88.9% and 94.4% in Geyi and Xize, respectively). In contrast, fungal assembly was dominated by stochastic processes (55.6% and 83.3%). Co-occurrence network analysis indicated that network complexity showed no significant differences among treatments at both sites, with positive correlations dominating the networks (> 82%). Two and nine key taxa were identified in Geyi and Xize, respectively, with Chloroflexi identified as a key taxon at both sites. Structural equation modelling indicated that changes in soil nutrients improved network stability directly or indirectly through increased β-diversity, increased contribution of deterministic assembly, and greater network complexity. Conclusions Intercropping with legumes better retains available nutrients. Bacterial communities showed greater sensitivity to post-tobacco rotation management. Both increases in β-diversity and greater contributions of deterministic assembly enhanced network stability. This study suggests that broadcasting green manure in Geyi and intercropping pea in Xize represent reasonable locally adapted management strategies for short-term post-tobacco rotation optimization.