Soil type determines the impact of simulated rainfall on desert microbiota. Rhazyia microbiome

Despite the aridity and low organic content of desert soils, they support diverse microbial communities that influence many biogeochemical processes. However, a better understanding of the microbial response to simulated rainfall is required to predict the impact of future changes in precipitation patterns. Here, we performed and in-situ experiment to investigate the effect of simulated rainfall on the bacterial communities in soils associated with shrubs of Rhazya stricta, a widespread perennial plant of medicinal and ecological ?importance?. The bacterial community composition was distinct between three different soil compartments: surface biological crusts, root-attached, and within the rhizosphere. Simulated rainfall had minor effects on the overall bacterial community composition, but some population-level responses were observed, especially in soil crusts where Betaproteobacteria, Sphingobacteria and Bacilli became more abundant after water addition. Within crusts (that had significantly higher organic carbon and nitrogen than the rhizosphere samples), there was a three-fold increase in bacterial biomass one week after watering; whereas bacterial biomass in the rhizosphere remained unchanged, despite the fact that the rhizosphere retained soil moisture for much longer. These findings suggest that crust microbiota were primarily water-limited, whereas the rhizosphere microbiota were co-limited by nutrients and water. Nevertheless, water-induced stimulation of microbial activities such as nitrification may be inferred from changes in bacterial populations and soil chemistry in the rhizosphere. These results indicate that between rainfall events, desert-soil microbial communities enter into stasis, with limited species turnover, and reactivate rapidly and relatively uniformly when water becomes available, rather than communities reassembling from preferentially-surviving inocula.

尽管荒漠土壤干旱缺水且有机质含量极低，但其仍孕育着多样的微生物群落，这些群落调控着诸多生物地球化学过程。然而，若要精准预测未来降水格局变化所带来的影响，我们需要更深入地理解微生物对模拟降雨的响应机制。本研究开展了原位实验，探究模拟降雨对硬枝假紫草（Rhazya stricta）灌丛关联土壤细菌群落的影响——硬枝假紫草是一种分布广泛的多年生植物，兼具药用与生态价值。三类不同土壤微生境的细菌群落组成存在显著差异：地表生物结皮（surface biological crusts）、根附着土壤以及根际土壤。模拟降雨对整体细菌群落组成的影响较为微弱，但观测到了部分种群水平的响应，尤其是在土壤结皮中：补水后，β-变形菌纲（Betaproteobacteria）、鞘脂杆菌纲（Sphingobacteria）与芽孢杆菌纲（Bacilli）的相对丰度显著提升。相较于根际土壤样本，生物结皮的有机碳与氮含量显著更高；补水一周后，结皮内的微生物生物量提升了三倍，而根际土壤的微生物生物量未发生变化——尽管根际土壤的持水时间显著更长。上述研究结果表明，生物结皮中的微生物群落主要受水分限制，而根际微生物群落则同时受到养分与水分的共同限制。尽管如此，从根际细菌种群与土壤化学性质的变化中，可以推断出补水会刺激硝化作用等微生物活动。本研究结果显示，在两次降雨事件之间，荒漠土壤微生物群落处于停滞状态，物种更替有限；当水分条件适宜时，群落会快速且相对均一地恢复活性，而非通过优先存活的接种体重新组装群落。