Institute of Botany, Czech Academy of Sciences, Department of Functional Ecology, Dukelská 135, CZ-379 82 Třeboň, Czech Republic; Faculty of Science, University of South Bohemia, Branišovská 1760, CZ-370 05 České Budějovice, Czech Republic.
Faculty of Science, Masaryk University, Department of Botany and Zoology, Kotlářská 2, CZ-611 37 Brno, Czech Republic.
Sci Total Environ. 2017 Feb 15;580:1429-1438. doi: 10.1016/j.scitotenv.2016.12.109. Epub 2016 Dec 27.
Sphagnum expansion to alkaline fens has accelerated during the last decades in Europe, leading to changes in diversity, habitat distributions and carbon storage. The causes are still not clearly understood and involve an interplay between climate change, hydrology, nutrient supply and Sphagnum physiology. We conducted a 4-year field experiment in eight fens in Central European highlands and assessed survival and establishment of individual apical shoot fragments of S. flexuosum, S. warnstorfii and S. squarrosum transplanted along the microtopographical gradient. In a laboratory experiment, we tested combined effects of desiccation and high calcium bicarbonate concentration on Sphagnum survival. We found that in unflooded positions, living shoots of Sphagnum and brown mosses lowered [Ca] and pH in their capillary water, in contrast to dead fragments; yet without differences between species. Survival and expansion of Sphagnum fragments, which did not die of acute calcium toxicity during first weeks/months, was negatively affected by dry weather and alkaline water chemistry, reflecting Sphagnum intolerance to desiccation and to combined high [Ca] and pH. Shoot fragments expanded to patches only when precipitation was high. Interestingly, non-toxic concentration of calcium bicarbonate reduced desiccation damage in Sphagnum, probably through protection of membranes or other cell components. This mechanism would facilitate Sphagnum survival in elevated, frequently desiccated microhabitats of calcareous fens such as brown-moss hummocks. However, since water-retaining capacity of few Sphagnum shoots is insufficient to change water chemistry in its surroundings, surface acidification may occur only once the environment (e.g. sufficient humidity) enabled expansion to larger mats. Then, the retained rainwater together with hardly decomposable Sphagnum litter would separate mire surface from groundwater, speeding up successional shift towards poor fens. Sphagnum expansion to alkaline fens is therefore more likely in humid regions.
欧洲过去几十年来，泥炭藓向碱性沼泽的扩张加速了，导致多样性、生境分布和碳储存发生变化。其原因仍不清楚，涉及气候变化、水文学、养分供应和泥炭藓生理学之间的相互作用。我们在中欧高地上的 8 个沼泽地进行了为期 4 年的野外实验，评估了沿微地形梯度移植的 S. flexuosum、S. warnstorfii 和 S. squarrosum 个体顶梢片段的存活和定植。在实验室实验中，我们测试了干燥和高碳酸钙浓度对泥炭藓存活的综合影响。我们发现，在未淹没的位置，活的泥炭藓和棕色苔藓的毛细管水降低了[Ca]和 pH 值，与死碎片相反；然而，不同物种之间没有差异。没有因急性钙毒性而在最初几周/几个月内死亡的泥炭藓碎片的存活和扩展受到干旱天气和碱性水化学的负面影响，反映出泥炭藓对干燥和高[Ca]和 pH 的不耐受。当降水高时，梢片段才会扩展到斑块。有趣的是，无毒浓度的碳酸钙减少了泥炭藓的干燥损伤，可能是通过保护膜或其他细胞成分。这种机制将有助于泥炭藓在钙质沼泽中经常干燥的升高微生境中生存，例如棕色苔藓丘。然而，由于少数泥炭藓梢的保水能力不足以改变其周围的水化学，只有当环境（例如足够的湿度）允许其扩展到更大的地衣垫时，表面酸化才会发生。然后，保留的雨水和几乎不可分解的泥炭藓凋落物将使沼泽表面与地下水分离，加速向贫瘠沼泽的演替转变。因此，在潮湿地区，泥炭藓向碱性沼泽的扩张更有可能。
