Data from: Draining the pool? Carbon storage and fluxes in three alpine plant communities

Shrub communities have expanded in arctic and alpine tundra during recent decades. Changes in shrub abundance may alter ecosystem carbon (C) sequestration and storage, with potential positive or negative feedback on global C cycling. To assess potential implications of shrub expansion in different alpine plant communities, we compared C fluxes and pools in one Empetrum-dominated heath, one herb- and cryptogam-dominated meadow, and one Salix-shrub community in Central Norway. Over two growing seasons, we measured Gross Ecosystem Photosynthesis, Ecosystem Respiration (ER), and C pools for above-ground vegetation, litter, roots, and soil separated into organic and mineral horizons. Both the meadow and shrub communities had higher rates of C fixation and ER, but the total ecosystem C pool in the meadow was twice that of the shrub community because of more C in the organic soil horizon. Even though the heath community had the lowest rates of C fixation, it stored one and a half times more C than the shrub community. The results indicate that the relatively high above-ground biomass sequestering C during the growing season is not associated with high C storage in shrub-dominated communities. Instead, shrub-dominated areas may be draining the carbon-rich alpine soils because of high rates of decomposition. These processes were not shown by mid-growing season C fluxes, but were reflected by the very different distribution of C pools in the three habitats.

近几十年来，北极与高山苔原的灌丛群落出现了扩张。灌丛丰度的变化可能会改变生态系统碳（C）固存与储存能力，进而对全球碳循环产生潜在的正负反馈效应。为评估不同高山植物群落中灌丛扩张的潜在影响，我们对比了挪威中部一处以帚石楠（Empetrum）为优势种的灌丛群落、一处以草本植物与隐花植物（cryptogam）为优势种的草甸群落，以及一处柳属（Salix）灌丛群落的碳通量与碳库特征。在两个生长季内，我们测定了总生态系统光合速率（Gross Ecosystem Photosynthesis）、生态系统呼吸（Ecosystem Respiration, ER），并分析了地上植被、枯落物、根系以及分为有机层和矿质层的土壤碳库。草甸与柳属灌丛群落的碳固定速率与生态系统呼吸速率均更高，但草甸群落的总生态系统碳库是柳属灌丛群落的两倍，这得益于其有机土层中储存了更多的碳。尽管帚石楠灌丛群落的碳固定速率最低，但其碳储存量却是柳属灌丛群落的1.5倍。研究结果表明，灌丛优势群落中，生长季较高的地上生物量碳固存能力并未伴随高碳储存量。相反，由于较高的分解速率，柳属灌丛分布区域可能正在消耗原本富碳的高山土壤碳库。上述过程无法通过生长季中期的碳通量观测体现，但可通过三类生境中碳库分布的显著差异得以反映。