Microbiome Propagation of Drought Legacy in Willow Rhizosphere. Plant Soil Feedback and Drought

The drought tolerance of crops may be improved by incorporating technologies that utilize rhizosphere microorganisms. Plant-microbe interactions influence plant physiology and soil properties relevant to drought resilience. Yet, we lack adequate understanding of the biology and ecology to apply these phenomena as a part of a management strategy. Here, we investigated the drought legacy effect in a two-phase experiment where the effect of drought on the rhizosphere microbiome was propagated. First, we tested whether plants differentially-select for microbial communities under drought. Then, we determined whether differences in starting communities effected the performance of a subsequent generation of plants under drought stress. Willow (Salix purpurea) were propagated via sterile cuttings to segregate the effects of microbial community as a mechanism of acclimation for plants under water stress. Drought had a significant and lasting impact on the structure of bacterial rhizosphere communities, resulting in higher estimated 16S rRNA gene copy number, higher diversity and increased populations of Actinobacteria and Chloroflexi. However, the propagation of drought-selected communities did not enhance plant tolerance to drought above controls. Conversely, communities propagated from the rhizospheres of watered controls reduced plant growth, with communities dominated by populations of Proteobacteria and Bacteroidetes. Eukaryote/fungal populations significantly declined in drought-affected rhizospheres, yet no consistent changes in community composition were apparent. Our findings demonstrate that the legacy of drought on the structure of rhizosphere microbial communities persisted throughout nine weeks of plant growth, independent of current water stress.