Impact of Ear Stage Drought Stress on Yield and Rhizosphere Metagenomic Profiles in Maize Cultivars with Contrasting Drought Tolerance

Background/Objectives: Drought stress is a primary constraint on maize productivity, yet the role of rhizosphere microbial communities in modulating cultivar-specific drought resilience remains poorly understood. This study aimed to investigate the physiological and microbiome-mediated responses underlying differences in drought tolerance between contrasting cultivars to better understand drought tolerance mechanisms. Methods: Two maize cultivars with contrasting drought tolerance—NK718 (tolerant) and Zhongdan 808 (sensitive)—were subjected to drought stress at the V12 stage. We assessed yield components, oxidative stress indicators (Malondialdehyde (MDA)), and antioxidant enzyme activities (Superoxide Dismutase (SOD), Peroxidase (POD), Catalase (CAT)). Metagenomic sequencing was employed to analyze structural and functional shifts in the rhizosphere microbiota. Results: Drought significantly suppressed yield and physiological performance in both cultivars. However, the sensitive cultivar suffered more pronounced yield losses and severe oxidative stress, indicated by elevated Malondialdehyde (MDA) and decreased antioxidant enzyme activities. Conversely, the tolerant cultivar maintained superior physiological homeostasis. Metagenomic sequencing revealed drought-induced microbial shifts, including decreased Proteobacteria and Ascomycota, alongside increased Actinobacteriota and Mucoromycota. Notably, the drought-tolerant cultivar exhibited enhanced microbial community stability and more complex co-occurrence networks. Furthermore, it enriched specific functional pathways, such as phenylpropanoid biosynthesis, which positively correlated with yield stability and antioxidant capacity. Conclusions: Maize drought tolerance is underpinned by the coordinated regulation of plant physiological adaptation and the structural and functional stabilization of the rhizosphere microbiome. These findings offer a theoretical framework for developing breeding strategies that leverage root-microbe interactions to optimize maize yields under water-limited conditions.