INIBIOMA (UNComahue-CONICET), Quintral 1250, 8400 San Carlos de Bariloche, Río Negro, Argentina.
Microb Ecol. 2010 Apr;59(3):533-45. doi: 10.1007/s00248-009-9627-4. Epub 2010 Jan 28.
The epilithic algae distribution along a pH gradient and the relationship between the chemical gradient and biomass development were studied in Río Agrio, a naturally acidic river located in Patagonia (Argentina). The epilithic community was monitored during the summer of three consecutive years in sites located above and below the entrance of tributaries. The epilithic community showed differences between sites based on the chemical composition of the water and the precipitates that appear on the streambed of the river. The lowest biomass, diversity, and number of species were found at the most extreme part of the river in terms of pH (ca. 2) and element concentrations. Euglena mutabilis was the dominant species in this section of the river. As pH increased (ca. 3), the community changed to be dominated by filamentous green algae (Ulothrix spp., Mougeotia sp., Klebsormidium sp.) showing luxuriant growths in terms of biomass. With the inflow of a neutral tributary, the pH of Río Agrio increased above 3, and the precipitates of orange-red iron hydroxides appeared. The algal community was not affected by these precipitates or the low P concentrations, along the next 30 km of river downstream from this site. The apparent physical stress that the precipitates impose on algae is in fact a dynamic reservoir of P because diel cycle of Fe could be promoting precipitation and redissolution processes that binds and releases P from these precipitates. Where the pH increased above 6, precipitates of aluminum hydroxides appeared. At this site, the epilithic biomass and density decreased, some algae species changed, but the diversity and the number of species in general remained consistent with the upstream values. The physical stress of the Al precipitates on the algae is added to the chemical stress that represents the sequestering of P in these precipitates that are not redissolved, resulting P a limiting nutrient for algae growth.
在巴塔哥尼亚（阿根廷）的天然酸性河流里亚格罗河，我们研究了沿 pH 梯度的附生藻类分布以及化学梯度与生物量发展之间的关系。在连续三年的夏季，我们在位于支流入口上方和下方的地点监测了附生群落。附生群落根据水的化学成分和出现在河床的沉淀物在不同地点之间存在差异。在 pH（约 2）和元素浓度方面最极端的河流部分，生物量、多样性和物种数量最低。在这条河的这一部分，Euglena mutabilis 是优势物种。随着 pH 值的升高（约 3），群落发生变化，丝状绿藻（Ulothrix spp.、Mougeotia sp.、Klebsormidium sp.）成为优势物种，生物量丰富。随着中性支流的流入，里亚格罗河的 pH 值上升到 3 以上，橙色-红色铁氢氧化物的沉淀物出现。在这个地点下游的接下来 30 公里的河流中，藻类群落没有受到这些沉淀物或低磷浓度的影响。沉淀物对藻类施加的明显物理压力实际上是磷的动态储库，因为铁的昼夜循环可以促进沉淀和再溶解过程，从而将磷从这些沉淀物中结合和释放出来。当 pH 值上升到 6 以上时，出现了铝氢氧化物的沉淀物。在这个地点，附生生物量和密度下降，一些藻类物种发生了变化，但总体多样性和物种数量与上游值保持一致。藻类受到铝沉淀物的物理压力，再加上磷被这些不溶解的沉淀物固定所带来的化学压力，使磷成为限制藻类生长的养分。
