In arctic and boreal ecosystems, ground bryophytes play an important role in regulating carbon (C) exchange between vast belowground C stores and the atmosphere. Climate is changing particularly fast in these high‐latitude regions, but it is unclear how altered precipitation regimes will affect C dynamics in the bryosphere (i.e. the ground moss layer including senesced moss, litter and associated biota) and the closely associated upper humus layer, and how these effects will vary across contrasting environmental conditions. Here, we set up a greenhouse experiment in which mesocosms were assembled containing samples of the bryosphere, dominated by the feather moss Hylocomium splendens, and the upper humus layer, that were collected from across a boreal forest chronosequence in northern Sweden which varies strongly in nutrient availability, productivity and soil biota. We tested the effect of variation in precipitation volume and frequency on CO₂ exchange and dissolved organic carbon (DOC) export, and on moss growth. As expected, reduced precipitation volume and frequency lowered net CO₂ efflux, DOC export and moss growth. However, by regulating moisture, the lower bryosphere and humus layers often mediated how precipitation volume and frequency interacted to drive C dynamics. For example, less frequent precipitation reduced moss growth only when precipitation volume was low. When volume was high, high moisture content of the humus layer helped avoid moss desiccation. Variation in precipitation regime affected C cycling consistently in samples collected across the chronosequence, despite large environmental variation along the sequence. This suggests that the bryosphere exerts a strong buffering effect on environmental variation at the forest floor, which leads to similar responses of C cycling to external perturbations across highly contrasting ecosystems. As such, our study indicates that projected increases in droughts and ground evapotranspiration in high‐latitude regions resulting from climate change will consistently reduce C losses from moss‐dominated ecosystems.

中文翻译：

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在不同的生态系统中，降水机制同样控制了Bryosphere碳循环

在北极和北方的生态系统中，地面苔藓植物在调节地下大量C碳库与大气之间的碳（C）交换中起着重要作用。在这些高纬度地区，气候变化特别迅速，但是目前尚不清楚降水方式的变化将如何影响苔藓层（即包括苔藓，凋落物和相关生物群的地面苔藓层）以及紧密相关的上腐殖质层中碳的动态变化，以及这些影响在不同的环境条件下如何变化。在这里，我们建立了一个温室实验，在该实验中，组装了以羽毛苔藓为首的Hylocomium splendens占主导地位的苔藓层样品以及上腐殖质层是从瑞典北部的一个北方森林时序序列中收集的，其养分利用率，生产力和土壤生物区系差异很大。我们测试了降水量和频率变化对CO ₂交换和溶解有机碳（DOC）出口以及苔藓生长的影响。不出所料，减少的降水量和频率降低了净CO ₂外排，DOC出口和苔藓生长。然而，通过调节水分，较低的苔藓层和腐殖质层通常介导降水量和频率如何相互作用以驱动碳动力学。例如，较少的降水仅在降水量较低时才减少苔藓的生长。当体积高时，腐殖质层的高水分含量有助于避免苔藓干燥。尽管整个序列的环境变化很大，但降水方式的变化始终在整个时间序列中影响样品中的C循环。这表明，苔藓层对森林底层的环境变化具有很强的缓冲作用，这导致碳循环对高度反差的生态系统中的外部扰动具有相似的响应。因此，