Microbial (bacterial and eukaryotic) community composition of transiently wetted Antarctic Dry Valley soils with comparisons to local arid soils.. Microbial community composition of transiently wetted vs. asrid Antarctic Dry Valley soils

During the summer months, wet (hyporheic) soils associated with ephemeral streams and lake edges in the Antarctic Dry Valleys (DV) become hotspots of biological activity and are hypothesized to be an important source of carbon and nitrogen for arid DV soils. Recent research in the DV has focused on the geochemistry and microbial ecology of lakes and arid soils, with substantially less information being available on hyporheic soils. Here we determined the unique properties of hyporheic microbial communities, resolved their relationship to environmental parameters and to compared them to archetypal arid DV soils. Generally, pH increased and chlorophyll a concentrations decreased along transects from wet to arid soils (9.0 to ~7.0 for pH and ~0.8 to ~ 5 µg/cm3 for chlorophyll a, respectively). Soil water content decreased to below ~3% in the arid soils. Community fingerprinting-based principle component analyses revealed that bacterial communities formed distinct clusters specific to arid and wet soils; however, eukaryotic communities that clustered together did not have similar soil moisture content nor did they group together based on sampling location. Collectively, rRNA pyrosequencing indicated a considerably higher abundance of Cyanobacteria in wet soils and a higher abundance of Acidobacterial, Actinobacterial, Deinococcus/Thermus, Bacteroidetes, Firmicutes, Gemmatimonadetes, Nitrospira and Planctomycetes in arid soils. The two most significant differences at the genus level were Gillisia signatures present in arid soils and chloroplast signatures related to Streptophyta that were common in wet soils. Fungal dominance was observed in arid soils and Viridplantae were more common in wet soils. This research represents an in-depth characterization of microbial communities inhabiting wet DV soils. Results indicate that the repeated wetting of hyporheic zones has a profound impact on the bacterial and eukaryotic communities inhabiting in these areas.

南极干谷（Antarctic Dry Valleys, 简称DV）的季节性溪流与湖岸周边的湿润潜流带（hyporheic）土壤，在夏季会成为生物活动热点区域，且被推测为干旱型干谷土壤重要的碳、氮来源。此前针对南极干谷的研究多聚焦于湖泊与干旱土壤的地球化学及微生物生态学特征，关于潜流带土壤的相关资料则相对匮乏。本研究明确了潜流带微生物群落的独特属性，解析了其与环境参数的关联，并将其与典型干旱型干谷土壤进行了对比。沿湿润至干旱土壤的样带，土壤pH值整体呈上升趋势，叶绿素a浓度则逐步下降（pH范围为9.0至约7.0，叶绿素a浓度范围为约0.8至5 µg/cm³）；干旱土壤的土壤含水量降至约3%以下。基于群落指纹图谱的主成分分析结果显示，细菌群落可形成与干旱、湿润土壤对应的独立聚类簇；但真核生物群落的聚类既未与土壤含水量呈现相关性，也未按采样地点进行分组。综合来看，rRNA焦磷酸测序（rRNA pyrosequencing）结果表明，湿润土壤中蓝细菌门（Cyanobacteria）的丰度显著更高；而干旱土壤中则富集了酸杆菌门（Acidobacterial）、放线菌门（Actinobacterial）、异常球菌-栖热菌门（Deinococcus/Thermus）、拟杆菌门（Bacteroidetes）、厚壁菌门（Firmicutes）、芽单胞菌门（Gemmatimonadetes）、硝化螺旋菌门（Nitrospira）与浮霉菌门（Planctomycetes）。在属水平上，两类土壤的最显著差异为干旱土壤中存在吉里斯菌属（Gillisia）特征类群，而湿润土壤中普遍存在与链形植物类群（Streptophyta）相关的叶绿体特征类群。干旱土壤呈现真菌优势度特征，湿润土壤中则以绿色植物类群（Viridplantae）更为常见。本研究实现了对南极干谷湿润土壤中微生物群落的深度表征，研究结果表明，潜流带区域的反复湿润过程，对栖息于此的细菌与真核生物群落具有显著影响。