Abstract:

Experiments were conducted to investigate the effects of warming and dominant plant species removal on net ecosystem CO₂ exchange (NEE), ecosystem respiration (ER) and gross ecosystem production (GEP) along elevational gradients (3200 m and 4000 m) in the alpine meadow on the Tibetan Plateau. The results showed that GEP was higher than ER at both elevations, indicating that both ecosystems were a net C sink during the growing season in 2017. At a lower elevation (3200 m), warming did not have a significant effect on ecosystem C flux due to water limitation caused by warming. At a wetter high elevation (4000 m), warming significantly stimulated ecosystem C fluxes, on average, the warming-induced increase in GEP (2.30 mg CO₂/(m²·s)) was higher than that in ER (0.62 mg CO₂/(m²·s)), leading to an increase in NEE. Dominant plant species removal did not have a significant effect on ecosystem C flux at either elevations, probably due to the compensatory effects of the remaining species, because the removal on above ground biomass (AGB) or below ground biomass (BGB) was not significant at both elevations. There was no significant interaction between warming and dominant species removal on the ecosystem C fluxes at either elevations. The results reveal the importance of soil moisture in mediating the response of ecosystem C flux to climate warming in alpine meadow ecosystems, and removal of a single dominant plant species may not have a significant impact on ecosystem C flux in species-rich regions.

Key words: alpine meadow, warming, dominant species removal, elevational gradients, ecosystem carbon fluxes

摘要：

在青藏高原高寒草甸的两个海拔梯度(3200 m 和 4000 m)上开展实验, 研究增温和优势植物物种去除对净生态系统CO₂交换量(NEE)、生态系统呼吸(ER)和生态系统总初级生产力(GEP)的影响。结果表明: 在2017年生长季, 两个海拔的GEP均高于ER, 表明这两个生态系统在生长季均表现为碳汇。低海拔(3200 m)的增温对生态系统C通量没有显著的作用, 原因可能是增温引起的水分限制。在较湿润的高海拔(4000 m)地区, 增温显著提高了生态系统C通量, 平均而言, 增温引起的GEP增加量(2.30 mg CO₂/(m²·s))高于ER (0.62 mg CO₂/(m²·s)), 导致NEE增加。两个海拔优势植物物种的去除对生态系统C通量均没有显著的作用, 原因可能是剩余物种的补偿作用, 因为去除处理对两个海拔的地上生物量(AGB)和地下生物量(BGB)的影响都不显著。增温和优势物种去除对两个海拔生态系统C通量没有显著的交互作用。研究结果揭示土壤湿度在调节高寒草甸生态系统C通量对气候变暖响应方面的重要性, 单一优势植物物种的去除可能不会对物种丰富的生态系统C通量产生较大的影响。

关键词: 高寒草甸, 增温, 优势物种去除, 海拔梯度, 生态系统碳通量