Table_6_Characterization of microbiomic and geochemical compositions across the photosynthetic fringe.XLSX

Hot spring outflow channels provide geochemical gradients that are reflected in microbial community compositions. In many hot spring outflows, there is a distinct visual demarcation as the community transitions from predominantly chemotrophs to having visible pigments from phototrophs. It has been hypothesized that this transition to phototrophy, known as the photosynthetic fringe, is a result of the pH, temperature, and/or sulfide concentration gradients in the hot spring outflows. Here, we explicitly evaluated the predictive capability of geochemistry in determining the location of the photosynthetic fringe in hot spring outflows. A total of 46 samples were taken from 12 hot spring outflows in Yellowstone National Park that spanned pH values from 1.9 to 9.0 and temperatures from 28.9 to 92.2°C. Sampling locations were selected to be equidistant in geochemical space above and below the photosynthetic fringe based on linear discriminant analysis. Although pH, temperature, and total sulfide concentrations have all previously been cited as determining factors for microbial community composition, total sulfide did not correlate with microbial community composition with statistical significance in non-metric multidimensional scaling. In contrast, pH, temperature, ammonia, dissolved organic carbon, dissolved inorganic carbon, and dissolved oxygen did correlate with the microbial community composition with statistical significance. Additionally, there was observed statistical significance between beta diversity and the relative position to the photosynthetic fringe with sites above the photosynthetic fringe being significantly different from those at or below the photosynthetic fringe according to canonical correspondence analysis. However, in combination, the geochemical parameters considered in this study only accounted for 35% of the variation in microbial community composition determined by redundancy analysis. In co-occurrence network analyses, each clique correlated with either pH and/or temperature, whereas sulfide concentrations only correlated with individual nodes. These results indicate that there is a complex interplay between geochemical variables and the position of the photosynthetic fringe that cannot be fully explained by statistical correlations with the individual geochemical variables included in this study.

热泉溢流通道所形成的地球化学梯度，其特征可通过微生物群落组成得以体现。在多数热泉溢流系统中，当微生物群落从以化能营养型为主，转变为出现光合营养型所产生的可见色素时，会形成清晰的视觉分界。此前有假说认为，这种向光合营养型的转变（被称为光合带（photosynthetic fringe）），其形成源于热泉溢流通道内的pH值、温度以及/或硫化物浓度梯度。本研究针对地球化学特征在确定热泉溢流通道内光合带位置的预测能力，开展了系统性验证。本研究从黄石国家公园的12处热泉溢流通道中共采集了46份样本，样本覆盖的pH值范围为1.9至9.0，温度范围为28.9至92.2℃。基于线性判别分析（linear discriminant analysis），采样点位被设置在光合带上下两侧的地球化学空间中，且二者在该空间内间距均等。尽管此前研究均将pH值、温度以及总硫化物浓度列为微生物群落组成的关键影响因子，但在非度量多维尺度分析（non-metric multidimensional scaling）中，总硫化物浓度与微生物群落组成并未呈现出具有统计学显著性的相关性。与之相反，pH值、温度、氨氮、溶解性有机碳、溶解性无机碳以及溶解氧均与微生物群落组成呈现出具有统计学显著性的相关性。此外，典范对应分析（canonical correspondence analysis）结果显示，β多样性与采样点相对于光合带的相对位置之间存在统计学显著性差异：光合带上方的采样点，其群落组成与光合带处或下方的采样点存在显著区别。然而，通过冗余分析（redundancy analysis）结果可知，本研究纳入的所有地球化学参数组合，仅能解释微生物群落组成35%的变异量。在共现网络分析中，各团簇均与pH值及/或温度呈现相关性，而硫化物浓度仅与单个网络节点存在关联。上述结果表明，地球化学变量与光合带位置之间存在复杂的相互作用，而本研究纳入的单一地球化学变量的统计学相关性，无法完全阐释这一相互作用机制。