Drought stress adaptation in Ficus carica L.: Modulation of ROS scavenging, nitrogen uptake, and rhizosphere bacterial community assembly and functions

Rhizosphere microorganisms are crucial for plant drought resistance; however, their response to drought stress in fig plants remains poorly understood. In this study, potted 'BoJi Red' fig plants were utilized to systematically investigate drought-induced changes in the structure, assembly processes, and functional potential of rhizosphere bacterial communities. The results showed that drought significantly inhibited fig growth, photosynthesis, and nitrogen uptake, while increasing reactive oxygen species (ROS) content and antioxidant enzyme activities, although these enzyme activities declined under severe drought conditions. Bacterial community richness and diversity significantly increased under moderate and severe drought, shifting toward drought-resistant groups, notably Actinomycetota and Bacillota. The number of nodes, links, and key species in the microbial co-occurrence network decreased as drought intensified, with stochastic processes dominating community assembly. Moreover, ecological niche breadth and the proportion of generalist species increased with drought severity. Notably, Nocardioidaceae was significantly enriched under drought, and metagenomic profiling indicated this taxon is strongly associated with carbohydrate metabolism pathways, with predicted genetic potential to participate in soil carbon turnover and nutrient transformation. Additionally, drought significantly reduced the abundance of nitrogen-fixing genes (nifD, nifK) and weakened the relative contribution of Rhizobiaceae to nitrogen fixation; correlative functional profiling suggests Nocardioidaceae may possess alternative nitrogen cycling pathways that could partially offset suppressed rhizosphere nitrogen fixation capacity. Overall, these findings indicate that the fig plant response to drought stress involves both physiological adjustments in the host and functional reconfiguration of the rhizosphere microbial community, with Nocardioidaceae playing a key role in maintaining rhizosphere functions and enhancing drought tolerance.