Drought alters the structure and assembly drivers of soil actinomycete and bacterial (non-Act.) communities in agroecosystems

Actinomycetes possess strong ecological resilience, enabling them to withstand drought while sustaining metabolic functionality. This adaptability allows them to play a crucial role in mitigating drought-induced impairments on crop growth. Yet, the mechanisms underlying Actinomycete community responses to drought remain poorly understood. To address this gap, we conducted a rain-shelter field experiment with graded water-deficit treatments, using arable soil collected from a conventional maize field. We examined the effects of drought on soil bacterial (non-actinomycete, non-act.) communities and the actinomycete communities, combining co-occurrence network analysis (CoNA) with squares structural equation models (SEM) to assess how drought shapes community structure and assembly. Our findings show that Actinomycete communities were more drought-resilient and maintained higher structural stability than bacteria (non-act.) communities. Both groups exhibited pronounced compositional changes from the jointing stage to filling stage of summer maize under drought conditions. CoNA showed that drought stress induced distinct network reorganization patterns in bacterial (non-act.) and actinobacterial communities. The bacterial (non-act.) network showed moderate increases in connectivity (edges: +5.62%, average degree: +14.11%) but minimal changes in modularity (−4.56%). In contrast, the actinomycete network exhibited more pronounced changes, with a 30.15% increase in edges and a 16.67% increase in graph density, indicating a more densely connected and complex network. This superior stability was further corroborated by robustness analysis, where actinobacteria exhibited stronger resistance to perturbations, characterized by a flatter robustness slope (-0.16 vs. −0.23) and lower vulnerability (0.0066 vs. 0.0112) compared to bacteria (non-act.), highlighting their critical role in maintaining ecological stability under water-limited conditions. Furthermore, SEM analysis identified Available Potassium (AK) as the primary positive driver for both bacterial (non-act.) (λ=0.836) and actinobacterial (λ=0.446) diversity. The model explained 53.8% of the variance in bacterial(non-act.) diversity, indicating high sensitivity to environmental fluctuations (e.g., AK and SWC). In contrast, the actinobacterial community (explained variance: 13.4%) exhibited attenuated responses to SWC deficits, providing compelling evidence of its superior ecological stability and drought resistance compared to bacteria (non-act.). Together, these findings reveal distinct drought-response strategies between (non-act.) and Actinomycete communities and provide new insights into the environmental controls governing microbial community assembly under drought in agricultural ecosystems.