Recent observations document increased abundance of algae in the headwater streams of Hubbard Brook Experimental Forest (HBEF). It is possible that this “greening up” of HBEF streams may be due to climate change, with rising temperatures, altering terrestrial phenology, and shifting hydrologic regimes. Alternatively, stream “greening” could be from the slow recovery of stream chemistry after decades of acid rain, which has led to rising pH, declining concentrations of toxic Al3+, and low solute concentrations. Four years of weekly algal measurements on artificial moss and ceramic tiles, along with six nutrient enrichment experiments, revealed new insights about the interactions between these two autotrophs. We found that in protected weir ponds and in stream channels, algal biomass was higher on artificial moss substrates than on tiles—with this effect amplified in the stream channels. These results suggest that bryophytes can provide physical protection from flood scour or may trap nutrients to support algal growth. In stream channels, algal biomass was higher in well‐lit habitats and time periods indicating strong light limitation. We only measured nitrogen and phosphorus limitation of algal biomass in nutrient enrichment experiments conducted within weir ponds, with higher light availability and lower flow. By comparison, results from the remaining four instream experiments provided little evidence for nutrient limitation, with only one trial showing increased algal growth in response to nutrient addition. The most striking implication of our study is the role of bryophytes in providing refugia, and potentially nutrients, to algae in shaded and oligotrophic headwater streams.

中文翻译：

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溪流苔藓植物在高度贫营养的源头促进“神秘”的生产力


最近的观察记录了哈伯德布鲁克实验森林 （HBEF） 源头溪流中藻类的丰度增加。HBEF 溪流的这种“绿化”可能是由于气候变化、气温升高、陆地物候改变和水文状况的变化。或者，溪流“绿化”可能是由于几十年的酸雨后溪流化学反应缓慢恢复，这导致 pH 值升高、有毒 Al3+ 浓度下降和溶质浓度低。四年来每周对人造苔藓和瓷砖进行藻类测量，以及六次营养富集实验，揭示了关于这两种自养生物之间相互作用的新见解。我们发现，在受保护的堰池和河道中，人造苔藓基质上的藻类生物量高于瓷砖上的藻类生物量——这种影响在河道中被放大。这些结果表明，苔藓植物可以提供物理保护免受洪水冲刷，或者可以捕获营养物质以支持藻类生长。在河道中，藻类生物量在光线充足的栖息地和表明强烈光照限制的时间段较高。在堰池内进行的营养富集实验中，我们只测量了藻类生物量的氮和磷限制，具有更高的光可用性和更低的流量。相比之下，其余四次溪流实验的结果几乎没有提供营养限制的证据，只有一项试验显示营养物质添加后藻类生长增加。我们研究最引人注目的意义是苔藓植物在为阴凉和贫营养源头溪流中的藻类提供避难所和潜在的营养方面的作用。