Effects of precipitation on rhizobacterial communities during plant growth: field and greenhouse experiments

Rhizosphere bacterial communities play a pivotal role in nutrient cycling, plant productivity, and soil ecosystem resilience. Understanding their response to precipitation variability is critical for predicting soil function under climate change, where droughts and heavy rainfall are becoming more frequent. Here, we investigated how precipitation influences rhizobacterial diversity and composition using a combination of multi-site field surveys and controlled greenhouse experiments with Aster koraiensis. Across three sites with contrasting climatic and soil conditions, rhizobacterial communities differed primarily according to soil physicochemical properties, while precipitation exerted additional effects on community structure. Greenhouse experiments with soils from all sites confirmed that reduced watering decreased bacterial α-diversity, whereas increased watering enhanced both microbial diversity and plant growth. Precipitation also altered nutrient dynamics, with higher NO₃ under watered treatments and greater uptake under plant presence. In particular, drought conditions enriched plant growth-promoting bacteria, suggesting functional resilience under water stress. Together, these findings demonstrate that precipitation regulates not only rhizobacterial composition but also the functional groups that sustain soil fertility and plant growth, highlighting the ecological significance of precipitation variability under climate change.