Koranda Marianne, Michelsen Anders
Terrestrial Ecology Section Department of Biology University of Copenhagen Copenhagen Denmark.
Center for Permafrost University of Copenhagen Copenhagen Denmark.
J Ecol. 2021 Mar;109(3):1424-1438. doi: 10.1111/1365-2745.13567. Epub 2020 Dec 21.
In high-latitude ecosystems bryophytes are important drivers of ecosystem functions. Alterations in abundance of mosses due to global change may thus strongly influence carbon (C) and nitrogen (N) cycling and hence cause feedback on climate. The effects of mosses on soil microbial activity are, however, still poorly understood. Our study aims at elucidating how and by which mechanisms bryophytes influence microbial decomposition processes of soil organic matter and thus soil nutrient availability.We present results from a field experiment in a subarctic birch forest in northern Sweden, where we partly removed the moss cover and replaced it with an artificial soil cover for simulating moss effects on soil temperature and moisture. We combined this with a fertilization experiment with N-labelled N for analysing the effects of moss N sequestration on soil processes.Our results demonstrate the capacity of mosses to reduce soil N availability and retard N cycling. The comparison with artificial soil cover plots suggests that the effect of mosses on N cycling is linked to the thermal insulation capacity of mosses causing low average soil temperature in summer and strongly reduced soil temperature fluctuations, the latter also leading to a decreased frequency of freeze-thaw events in autumn and spring. Our results also showed, however, that the negative temperature effect of mosses on soil microbial activity was in part compensated by stimulatory effects of the moss layer, possibly linked to leaching of labile substrates from the moss. Furthermore, our results revealed that bryophytes efficiently sequester added N from wet deposition and thus prevent effects of increased atmospheric N deposition on soil N availability and soil processes. . Our study emphasizes the important role of mosses in carbon and nutrient cycling in high-latitude ecosystems and the potential strong impacts of reductions in moss abundance on microbial decomposition processes and nutrient availability in subarctic and boreal forests.
在高纬度生态系统中，苔藓植物是生态系统功能的重要驱动因素。因此，全球变化导致的苔藓丰度改变可能会强烈影响碳（C）和氮（N）循环，进而对气候产生反馈。然而，苔藓对土壤微生物活动的影响仍知之甚少。我们的研究旨在阐明苔藓植物如何以及通过何种机制影响土壤有机质的微生物分解过程，从而影响土壤养分有效性。我们展示了瑞典北部亚北极桦树林实地实验的结果，在该实验中，我们部分移除了苔藓覆盖物，并用人工土壤覆盖物取而代之，以模拟苔藓对土壤温度和湿度的影响。我们将此与使用氮标记氮的施肥实验相结合，以分析苔藓固氮对土壤过程的影响。我们的结果表明，苔藓有能力降低土壤氮有效性并减缓氮循环。与人工土壤覆盖地块的比较表明，苔藓对氮循环的影响与苔藓的隔热能力有关，导致夏季土壤平均温度较低，土壤温度波动大幅降低，后者还导致秋季和春季冻融事件的频率降低。然而，我们的结果还表明，苔藓对土壤微生物活动的负温度效应部分被苔藓层的刺激效应所补偿，这可能与苔藓中不稳定底物的淋溶有关。此外，我们的结果表明，苔藓植物能有效固定来自湿沉降的添加氮，从而防止大气氮沉降增加对土壤氮有效性和土壤过程的影响。我们的研究强调了苔藓在高纬度生态系统碳和养分循环中的重要作用，以及苔藓丰度降低对亚北极和北方森林微生物分解过程和养分有效性的潜在强烈影响。
