Bacterial diversity of Agave lechugilla rizosphere in Cuatro Cienegas Basin

Due to the environmental conditions presented in arid zones, it is expected to have a high influence of deterministic processes over the community assemblages. Plants living in this habitats are well adapted to survive this difficult conditions but independently of their physiologic and morphological adaptations, the symbiotic interactions with microorganisms could be strengthen, facilitating colonization and survival. In this context, the microbial communities associated to plants that inhabit these types of areas can be a good model to understand the community assembly processes. In this study, we investigated the influence of deterministic and stochastic processes in the assemblage of rhizosphere microbial communities of Agave lechuguilla and bulk soil on the Cuatro Cienegas Valley, a site known for its oligotrophic conditions. We proposed two hypotheses: 1) Microbial co-occurrence patterns in Agave lechuguilla rhizosphere are distinct from those in bulk soil, which is affected by both abiotic and biotic factors (season and physicochemical properties of soil and plant interactions, respectively); 2) The keystone microbial species are usually critical for plant growth and health in the rhizosphere, whereas in the bulk soil they are related to the resistance to abiotic stress. In order to confirm this hypothesis, 16S rRNA gene was sequenced by Illumina from rhizospheric and bulk soil samples in two seasons, also the physicochemical properties of the soil were determined. Our results showed differences in bacterial diversity, community composition, potential functions and interaction networks between the rhizosphere samples and the ones from the bulk soil. Despite patterns of community structure depend on a complex balance between deterministic and stochastic forces acting on populations at different spatial scales and within different functional groups, our results suggest that Agave lechuguilla selects a specific microbial community inhabiting the rhizosphere based on functional traits, which may be related to benefits to the plant, as growth promotion and nutrition.

鉴于干旱地带的环境特征，确定性过程对群落组装的影响预计将占据主导地位。栖息于此类生境的植物已演化出良好适应性以应对严苛环境；但无论其生理与形态适应性如何，与微生物的共生互作均可能得到强化，从而助力微生物的定殖与存活。在此背景下，栖息于这类区域的植物相关微生物群落，可作为研究群落组装过程的优质模型。本研究以以贫营养环境著称的夸特罗谢内加斯谷地（Cuatro Cienegas Valley）为研究地点，探究了确定性与随机性过程对龙舌兰（Agave lechuguilla）根际微生物群落及非根际土壤微生物群落组装的影响。我们提出两项假说：其一，龙舌兰根际的微生物共现模式与非根际土壤存在显著差异，二者分别受非生物因素（土壤季节变化与理化性质）与生物因素（植物互作）的调控；其二，根际的关键微生物类群通常对植物生长与健康至关重要，而非根际土壤中的关键微生物类群则与非生物胁迫抗性相关。为验证上述假说，本研究于两个季节采集根际与非根际土壤样品，通过Illumina测序平台对16S rRNA基因进行测序，并测定了土壤的理化性质。研究结果显示，根际土壤样品与非根际土壤样品在细菌多样性、群落组成、潜在功能及互作网络方面均存在显著差异。尽管群落结构模式取决于不同空间尺度与不同功能类群下，作用于种群的确定性与随机性力量之间的复杂平衡，但本研究结果表明，龙舌兰会基于功能性状筛选其根际的特异性微生物群落，这类群落或可通过促生长、改善营养等方式为植物带来益处。