Data_Sheet_1_Relieving your stress: PGPB associated with Andean xerophytic plants are most abundant and active on the most extreme slopes.PDF

IntroductionPlants interact with plant growth-promoting bacteria (PGPB), especially under stress condition in natural and agricultural systems. Although a potentially beneficial microbiome has been found associated to plants from alpine systems, this plant- PGPB interaction has been scarcely studied. Nevados de Chillán Complex hold one of the southernmost xerophytic formations in Chile. Plant species living there have to cope with drought and extreme temperatures during the growing season period, microclimatic conditions that become harsher on equatorial than polar slopes, and where the interaction with PGPB could be key for plant survival. Our goal was to study the abundance and activity of different PGPB associated to two abundant plant species of Andean xerophytic formations on contrasting slopes.MethodsTwenty individuals of Berberis empetrifolia and Azorella prolifera shrubs were selected growing on a north and south slope nearby Las Fumarolas, at 2,050 m elevation. On each slope, microclimate based on temperature and moisture conditions were monitored throughout the growing period (oct. – apr.). Chemical properties of the soil under plant species canopies were also characterized. Bacterial abundance was measured as Log CFU g−1 from soil samples collected from each individual and slope. Then, the most abundant bacterial colonies were selected, and different hormonal (indoleacetic acid) and enzymatic (nitrogenase, phosphatase, ACC-deaminase) mechanisms that promote plant growth were assessed and measured.Results and DiscussionExtreme temperatures were observed in the north facing slope, recording the hottest days (41 vs. 36°C) and coldest nights (−9.9 vs. 6.6°C). Moreover, air and soil moisture were lower on north than on south slope, especially late in the growing season. We found that bacterial abundance was higher in soils on north than on south slope but only under B. empetrifolia canopy. Moreover, the activity of plant growth-promoting mechanisms varied between slopes, being on average higher on north than on south slope, but with plant species-dependent trends. Our work showed how the environmental heterogeneity at microscale in alpine systems (slope and plant species identity) underlies variations in the abundance and plant growth promoting activity of the microorganisms present under the plant canopy of the Andean xerophytic formations and highlight the importance of PGPB from harsh systems as biotechnological tools for restoration.

引言：植物与促进植物生长的细菌（PGPB）相互作用，尤其是在自然和农业系统中的逆境条件下。尽管在高山系统中发现的潜在有益微生物群与植物相关联，但这种植物-PGPB相互作用的研究尚属罕见。内华达斯奇连火山复合体拥有智利最南端的旱生植被之一。生活于此的植物物种必须应对生长季节期间的干旱和极端温度，这些微气候条件在赤道斜坡上比极地斜坡更为严酷，而与PGPB的相互作用可能对植物的生存至关重要。我们的目标是研究与安第斯旱生植被中两种丰富植物物种相关的不同PGPB的丰度和活性。方法：在海拔2,050米的拉富马罗拉斯附近，选择了20株生长在南北斜坡上的欧亚连枷和欧亚连枷灌木。在每个斜坡上，对基于温度和湿度条件的微气候进行了整个生长季节（10月-4月）的监测。同时，对植物物种冠下的土壤化学性质也进行了表征。通过从每个个体和斜坡采集的土壤样本，测量了细菌丰度，以Log CFU g−1表示。然后，选择了最丰富的细菌菌落，并评估和测量了促进植物生长的不同激素（吲哚乙酸）和酶促（固氮酶、磷酸酶、ACC-脱氨酶）机制。结果与讨论：在北向斜坡上观察到了极端温度，记录了最热的一天（41°C对36°C）和最冷的夜晚（-9.9°C对6.6°C）。此外，空气和土壤湿度在北斜坡上低于南斜坡，尤其是在生长季节后期。我们发现，在北斜坡的土壤中细菌丰度高于南斜坡，但仅在欧亚连枷冠下。此外，促进植物生长的机制活性在不同斜坡之间有所差异，平均而言，北斜坡高于南斜坡，但存在植物物种依赖的趋势。我们的研究揭示了高山系统中微尺度环境异质性（斜坡和植物物种身份）如何导致安第斯旱生植被下植物冠层中微生物的丰度和促进植物生长的活性发生变异，并强调了来自恶劣系统的PGPB作为恢复生物技术工具的重要性。