Department of Plant Ecology, Evolutionary Biology Center, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden.
Ecology. 2010 Oct;91(10):3047-56. doi: 10.1890/09-2267.1.
Stratigraphic records from peatlands suggest that the shift from a rich fen (calcareous fen) to an ombrotrophic bog can occur rapidly. This shift constitutes a switch from a species-rich ecosystem to a species-poor one with greater carbon storage. In this process, the invasion and expansion of acidifying bog species of Sphagnum (peat mosses) play a key role. To test under what conditions an acidifying bog species could invade a rich fen, we conducted three experiments, contrasting the bog species S. fucsum with the rich-fen species S. warnstorfii and S. teres. We first tested the effect of calcareous water by growing the three species at different constant height above the water table (HWT; 2, 7, and 14 cm) in a rich-fen pool and measured maximum photosynthetic rate and production and difference in length growth as an indicator of competition. In none of the species was the photosynthetic capacity negatively affected when placed at low HWT, but S. fuscum was a weaker competitor at low HWT. In our second experiment we transplanted the three species into microhabitats with different and naturally varying HWT in a rich fen. Here, S. fuscum nearly ceased to photosynthesize when transplanted to low HWT (brown moss carpet), while it performed similarly to the two rich-fen species at the intermediate level (S. warnstorfii hummock level). In contrast to S. fuscum, the rich-fen sphagna performed equally well in both habitats. The brown moss carpet was seasonally flooded, and in our third experiment we found that S. fuscum, but not S. teres, was severely damaged when submerged in rich-fen water. Our results suggest two thresholds in HWT affecting the ecosystem switch: one level that reduces the risk of submergence and a higher one that makes bog sphagna competitive against the rich-fen species.
从泥炭地的地层记录来看，富营养沼泽（钙质沼泽）向寡营养沼泽的转变可能会迅速发生。这种转变构成了从一个物种丰富的生态系统到一个物种较少但碳储量更大的生态系统的转变。在这个过程中，酸化沼泽种泥炭藓（泥炭藓）的入侵和扩张起着关键作用。为了测试酸化沼泽种在什么条件下可以入侵富营养沼泽，我们进行了三项实验，对比了沼泽种 S. fucsum 与富营养沼泽种 S. warnstorfii 和 S. teres。我们首先通过在富营养沼泽池中不同的恒定水位（HWT；2、7 和 14 cm）上生长这三个物种，来测试钙质水的影响，并测量最大光合作用率和生产力以及长度生长差异作为竞争的指标。在所有物种中，当放置在低 HWT 时，光合作用能力都没有受到负面影响，但 S. fuscum 在低 HWT 时竞争力较弱。在我们的第二项实验中，我们将这三个物种移植到富营养沼泽中具有不同自然变化 HWT 的微生境中。在这里，当移植到低 HWT（棕色苔藓地毯）时，S. fuscum 几乎停止光合作用，而在中间水平（S. warnstorfii 丘顶水平）时，它与两种富营养沼泽种的表现相似。与 S. fuscum 相反，富营养沼泽种在这两种栖息地中表现都一样好。棕色苔藓地毯会季节性地被淹没，在我们的第三个实验中，我们发现 S. fuscum 但不是 S. teres 在富营养沼泽水中淹没时会受到严重损害。我们的结果表明，有两个 HWT 阈值会影响生态系统的转变：一个是降低淹没风险的水平，另一个是使沼泽泥炭藓具有竞争力的更高水平。
