A history of drought exposure promoted by variable precipitation regimes can select for drought-tolerant soil microbial taxa, but the mechanisms of survival and death of microbial populations through the selective stresses of soil drying and re-wet are not well understood. We subjected soils collected from a 15-year field drought experiment ("Altered" precipitation history with extended dry periods, versus the "Ambient" field control) to a laboratory drying/re-wetting experiment, to learn whether selective population survival, death, or maintenance of protein synthesis potential and microbial respiration through variable soil water conditions was affected by field drought legacy. Microbial community composition, as measured by Illumina MiSeq sequencing of the 16S rRNA and 16S rRNA gene, shifted with laboratory drying/re-wet and field drought treatments. In Ambient soils, there was a higher proportion of reduced OTU abundance (indicative of mortality) during re-wet, whereas Altered soils had a greater proportion of stable OTU populations that did not change in abundance (indicative of survival) through drying/re-wet. Altered soils also had a lower proportion of rRNA:rRNA genes (lower protein synthesis potential) during dry-down, a greater weighted mean rRNA operon number (potential growth rate and r-selection) which was associated with higher abundance of Firmicutes (order Bacillales), and lower average microbial respiration rates. These data demonstrate that soils with a weaker historical drought legacy exhibit a higher prevalence of microbial water-stress mortality and differential survival and death at OTU levels following short-term dryingand re-wetting, concurrent with higher carbon loss potential. This work provides novel insight into the mechanisms and consequences of soil microbial changes resulting from extended drought conditions.

中文翻译：

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历史干旱影响土壤干燥和再湿期间的微生物种群动态和活性。

由不同的降水方式促进干旱暴露的历史可以选择耐旱的土壤微生物类群，但通过土壤干燥和再湿的选择性胁迫，微生物种群的生存和死亡机制尚未得到很好的理解。我们对一项15年的野外干旱实验（“干旱”的降水历史记录，具有延长的干旱时间，而“环境”野外控制）的土壤进行了实验室干燥/再湿润实验，以了解是否有选择性的种群存活，死亡，在田间干旱的影响下，通过变化的土壤水分条件维持或维持蛋白质合成潜能和微生物呼吸的能力受到影响。通过16S rRNA和16S rRNA基因的Illumina MiSeq测序测得的微生物群落组成，转移了实验室干燥/再湿和田间干旱处理。在环境土壤中，湿润期间降低的OTU丰度（指示死亡）的比例更高，而蚀变土壤具有稳定的OTU种群的比例更大，其通过干燥/再干燥不会改变其丰度（指示存活）。湿。在干燥过程中，改变的土壤还具有较低的rRNA：rRNA基因比例（较低的蛋白质合成潜力），较大的加权平均rRNA操纵子数（潜在生长率和r-选择），这与​​较高的Firmicutes（有序芽孢杆菌）相关），并降低平均微生物呼吸速率。这些数据表明，历史干旱较弱的土壤在短期干燥和再湿润后，在OTU水平上表现出较高的微生物水分胁迫死亡率和不同的存活率和死亡率，同时具有较高的碳损失潜力。这项工作提供了新的见解，以了解干旱造成的土壤微生物变化的机制和后果。