Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Center for Permafrost (CENPERM), University of Copenhagen, Copenhagen, Denmark.
Glob Chang Biol. 2024 Jul;30(7):e17401. doi: 10.1111/gcb.17401.
Climate change in high latitude regions leads to both higher temperatures and more precipitation but their combined effects on terrestrial ecosystem processes are poorly understood. In nitrogen (N) limited and often moss-dominated tundra and boreal ecosystems, moss-associated N fixation is an important process that provides new N. We tested whether high mean annual precipitation enhanced experimental warming effects on growing season N fixation in three common arctic-boreal moss species adapted to different moisture conditions and evaluated their N contribution to the landscape level. We measured in situ N fixation rates in Hylocomium splendens, Pleurozium schreberi and Sphagnum spp. from June to September in subarctic tundra in Sweden. We exposed mosses occurring along a natural precipitation gradient (mean annual precipitation: 571-1155 mm) to 8 years of experimental summer warming using open-top chambers before our measurements. We modelled species-specific seasonal N input to the ecosystem at the colony and landscape level. Higher mean annual precipitation clearly increased N fixation, especially during peak growing season and in feather mosses. For Sphagnum-associated N fixation, high mean annual precipitation reversed a small negative warming response. By contrast, in the dry-adapted feather moss species higher mean annual precipitation led to negative warming effects. Modelled total growing season N inputs for Sphagnum spp. colonies were two to three times that of feather mosses at an area basis. However, at the landscape level where feather mosses were more abundant, they contributed 50% more N than Sphagnum. The discrepancy between modelled estimates of species-specific N input via N fixation at the moss core versus ecosystem scale, exemplify how moss cover is essential for evaluating impact of altered N fixation. Importantly, combined effects of warming and higher mean annual precipitation may not lead to similar responses across moss species, which could affect moss fitness and their abilities to buffer environmental changes.
高纬度地区的气候变化既导致气温升高，又导致降水增加，但人们对其对陆地生态系统过程的综合影响知之甚少。在氮（N）限制且通常以苔藓为主的苔原和北方森林生态系统中，与苔藓相关的 N 固定是提供新 N 的重要过程。我们测试了高平均年降水量是否增强了三种适应不同水分条件的常见北极-北方苔藓物种在实验性生长季节 N 固定中的变暖效应，并评估了它们对景观水平的 N 贡献。我们在瑞典亚北极苔原的自然降水梯度（平均年降水量：571-1155 毫米）上测量了 Hylocomium splendens、Pleurozium schreberi 和 Sphagnum spp. 的原位 N 固定速率。在我们的测量之前，我们使用开顶室对苔藓进行了 8 年的夏季变暖实验，暴露在自然降水梯度上的苔藓（平均年降水量：571-1155 毫米）。我们在殖民地和景观水平上对特定物种的季节性 N 输入进行了建模。高平均年降水量明显增加了 N 固定，尤其是在生长季节高峰期和羽毛苔藓中。对于 Sphagnum 相关的 N 固定，高平均年降水量扭转了对变暖的小的负响应。相比之下，在干燥适应的羽毛苔藓物种中，高平均年降水量导致了变暖的负响应。基于面积的 Sphagnum spp. 殖民地的整个生长季节 N 输入的模型估计是羽毛苔藓的两到三倍。然而，在苔藓更丰富的景观水平上，它们的 N 贡献比 Sphagnum 多 50%。通过 N 固定在苔藓核心与生态系统尺度上对特定物种的 N 输入的模型估计之间的差异，说明了苔藓覆盖对于评估改变的 N 固定的影响是必不可少的。重要的是，变暖与高平均年降水量的综合效应可能不会导致不同苔藓物种的反应相似，这可能会影响苔藓的适应能力及其缓冲环境变化的能力。
