Stable soil moisture promotes shoot performance and shapes the root-rhizosphere microbiome

Soil moisture is a key factor limiting crop productivity and has been widely studied to optimize agriculture production. However, the majority of previous studies focus only on the soil moisture content and ignore its temporal variation. This study investigates the impact of different soil moisture conditions, specifically fluctuating soil moisture (FSM) and stable soil moisture (SSM), on the rhizosphere microbiome and the plant performance of romaine lettuce. Plants were grown in natural and sterilized soils, which were subjected to SSM through negative pressure irrigation to achieve high, mid, and low moisture levels and FSM through manual irrigation. Shoot performance parameters, such as plant height, leaf count, -size, and biomass, were significantly enhanced under SSM compared to FSM. The findings reveal SSM enhances shoot performance and crop water productivity (WPc) independent of root size, as indicated by a lower root/shoot ratio. Analyses of the soil microbiome showed that the root-associated rhizosphere microbial community composition differs for SSM and FSM conditions, while the bulk soil microbial community was unaffected. This suggests that the response of the romaine lettuce rhizosphere microbial community to soil moisture temporal variation is driven by root microbiome interactions. This study indicates that stable soil moisture, together with the recruited root microbiome, induces shoot performance without enhancing root growth. Overall, the findings highlight the importance of optimizing soil moisture dynamics to improve plant growth and resource efficiency, offering valuable implications for sustainable agricultural practices.