Mountain Ecosystems, WSL Institute for Snow and Avalanche Research-SLF, Flüelastrasse 11, 7260 Davos Dorf, Switzerland.
Oecologia. 2013 Mar;171(3):623-37. doi: 10.1007/s00442-012-2576-5. Epub 2013 Jan 23.
We evaluated the impacts of elevated CO2 in a treeline ecosystem in the Swiss Alps in a 9-year free-air CO2 enrichment (FACE) study. We present new data and synthesize plant and soil results from the entire experimental period. Light-saturated photosynthesis (A max) of ca. 35-year-old Larix decidua and Pinus uncinata was stimulated by elevated CO2 throughout the experiment. Slight down-regulation of photosynthesis in Pinus was consistent with starch accumulation in needle tissue. Above-ground growth responses differed between tree species, with a 33 % mean annual stimulation in Larix but no response in Pinus. Species-specific CO2 responses also occurred for abundant dwarf shrub species in the understorey, where Vaccinium myrtillus showed a sustained shoot growth enhancement (+11 %) that was not apparent for Vaccinium gaultherioides or Empetrum hermaphroditum. Below ground, CO2 enrichment did not stimulate fine root or mycorrhizal mycelium growth, but increased CO2 effluxes from the soil (+24 %) indicated that enhanced C assimilation was partially offset by greater respiratory losses. The dissolved organic C (DOC) concentration in soil solutions was consistently higher under elevated CO2 (+14 %), suggesting accelerated soil organic matter turnover. CO2 enrichment hardly affected the C-N balance in plants and soil, with unaltered soil total or mineral N concentrations and little impact on plant leaf N concentration or the stable N isotope ratio. Sustained differences in plant species growth responses suggest future shifts in species composition with atmospheric change. Consistently increased C fixation, soil respiration and DOC production over 9 years of CO2 enrichment provide clear evidence for accelerated C cycling with no apparent consequences on the N cycle in this treeline ecosystem.
我们在瑞士阿尔卑斯山的一个林线生态系统中进行了为期 9 年的大气 CO2 富集（FACE）研究，评估了 CO2 升高的影响。我们呈现了新的数据，并综合了整个实验期间植物和土壤的结果。在整个实验过程中，约 35 年生的欧洲赤松和欧洲云杉的光饱和光合作用（A max）受到 CO2 升高的刺激。在针叶组织中淀粉积累导致 Pinus 的光合作用略有下调。地上生长响应因树种而异，欧洲赤松的平均年增长率为 33%，而欧洲云杉则没有响应。林下丰富的矮灌木物种也表现出了特定于物种的 CO2 响应，其中 Vaccinium myrtillus 的枝条生长持续增强（+11%），而 Vaccinium gaultherioides 或 Empetrum hermaphroditum 则没有。地下，CO2 富集并没有刺激细根或菌根菌丝的生长，但增加了土壤 CO2 排放（+24%），这表明增强的 C 同化部分被呼吸损失所抵消。土壤溶液中溶解有机碳（DOC）的浓度在 CO2 升高下一直较高（+14%），这表明土壤有机质的周转加速。CO2 富集几乎没有影响植物和土壤中的 C-N 平衡，土壤总氮或矿质氮浓度没有变化，植物叶片氮浓度或稳定氮同位素比值也没有变化。植物物种生长响应的持续差异表明，随着大气变化，未来物种组成将发生变化。在 CO2 富集的 9 年中，持续增加的 C 固定、土壤呼吸和 DOC 产生提供了明确的证据，表明 C 循环加速，而氮循环在这个林线生态系统中没有明显的变化。
