Alleviation of water‐deficit inhibition of plant growth by rhizosphere microbiota conditioning

Summary Rhizosphere microbiota conditioning is a promising strategy to enhance plant growth. We conditioned the rhizosphere microbiota of Brassica juncea to water deficit to assess its impact on plant growth. In a glasshouse, plants were first grown under well‐watered conditions, then exposed to moderate (MD, pF = 2.3) or extreme (ED, pF = 3.5) water deficits. We extracted and inoculated the rhizosphere microbiota to new plants and repeated this process 10 times. Control plants were kept well‐watered. We monitored changes in plant phenotypes and in rhizosphere microbial communities (bacteria and eukaryotes). The initial water‐deficit growth inhibition of plants was successfully alleviated by 19.3% in MD and 29.4% in ED after conditioning (MD: from −35.6% to −16.3%; ED: from −56.8% to −27.4%). This beneficial effect on plants was not observed during the well‐watered phases, suggesting an active role of the microbiota when water became scarce. The increase in plant growth correlated with aggregated rhizosphere soil and significantly matched changes in the bacterial community, featuring reduced diversity and increased biofilm production capacity along the conditioning process. We showed that microbiota conditioning was a fast and efficient way to achieve better plant growth under adverse conditions, likely via the adaptation capabilities of the rhizosphere bacterial community.