Microbiome Propagation of Drought Legacy in Willow Rhizosphere

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.

通过利用根际微生物（rhizosphere microorganisms）相关技术，可提升作物的抗旱性。植物-微生物互作（plant-microbe interactions）会影响植物生理特性以及与抗旱恢复力相关的土壤性质。然而，当前我们对相关生物学与生态学机制的认知仍不足以将这些现象应用于农业管理策略中。本研究通过两阶段实验探究干旱遗留效应，以此传递干旱对根际微生物组（rhizosphere microbiome）的影响：首先验证植物在干旱条件下是否会差异化选择微生物群落，其次明确初始群落的差异是否会影响后续世代植物在干旱胁迫下的生长表现。本研究以紫柳（Salix purpurea）为受试材料，通过无菌扦插繁殖的方式分离微生物群落作为植物在水分胁迫下的驯化机制。干旱对细菌根际群落结构产生了显著且持久的影响，具体表现为16S核糖体RNA基因（16S rRNA gene）拷贝数估计值更高、群落多样性更丰富，且放线菌门（Actinobacteria）与绿弯菌门（Chloroflexi）的种群丰度显著提升。然而，经干旱筛选的微生物群落并未使植物的耐旱性较对照组得到改善。与之相反，取自浇水对照组根际的微生物群落反而抑制了植物生长，这类群落以变形菌门（Proteobacteria）与拟杆菌门（Bacteroidetes）的种群为主。干旱影响的根际环境中，真核/真菌种群数量显著下降，但群落组成未出现显著且一致的变化。本研究结果表明，干旱对根际微生物群落结构造成的遗留效应在整个九周的植物生长期内持续存在，且不受当前水分胁迫状态的影响。