State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, People's Republic of China.
University of Chinese Academy of Sciences, Beijing, 100049, People's Republic of China.
Environ Sci Pollut Res Int. 2018 Sep;25(26):26576-26591. doi: 10.1007/s11356-018-2724-5. Epub 2018 Jul 11.
The alpine meadow ecosystem is one of the major vegetation biomes on the Qinghai-Tibetan Plateau, which hold substantial quantities of soil organic carbon. Pronounced grassland degradations (induced by overgrazing/climate change and further exacerbated by the subterranean rodent activities) that have widely occurred in this ecosystem may significantly alter the non-growing season carbon turnover processes such as carbon dioxide (CO) efflux, but little is known about how the non-growing season CO emissions respond to the degradation (particularly the exacerbated degradations by plateau zokor), as most previous studies have focused primarily on the growing season. In this study, the effects of four degradation levels (i.e., the healthy meadow (HM), degraded patches (DP), 2-year-old zokor mounds (ZM2), and current-year zokor mounds (ZM1)) on CO emissions and corresponding environmental and agronomic variables were investigated over the two non-growing seasons under contrasting climatic conditions (a normal season in 2013-2014 and a "warm and humid" season in 2014-2015). The temporal variation in the non-growing season CO emissions was mainly regulated by soil temperature, while increasing degradation levels reduced the temperature sensitivity of CO emissions due to a reduction in soil water content. The cumulative CO emissions across the non-growing season were 587-1283 kg C ha for all degradation levels, which varied significantly (p < 0.05) interannually. The degradation of alpine meadows significantly (p < 0.05) reduced the vegetation cover and aboveground net primary productivity as well as the belowground biomass, which are typically thought to decrease soil CO emissions. However, the non-growing season CO emissions for the degraded meadow, weighted by the areal extent of the DP, ZM2, and ZM1, were estimated to be 641-1280 kg C ha, which was significantly higher (p < 0.05) as compared with the HM in the warm and humid season of 2014-2015 but not in the normal season of 2013-2014. Additionally, grassland degradation substantially increased the productivity-scaled non-growing season CO emissions, which showed an exponential trend with increasing degradation levels. These results suggest that there is a strong connection between grassland degradation and soil carbon loss, e.g., in the form of CO release, pointing to the urgent need to manage degraded grassland restoration that contributes to climate change mitigation.
高山草甸生态系统是青藏高原主要的植被生物群系之一，它含有大量的土壤有机碳。在这个生态系统中，普遍发生的强烈草地退化（由过度放牧/气候变化引起，并进一步因地下啮齿动物活动而加剧）可能会显著改变非生长季节的碳转化过程，如二氧化碳（CO）排放，但对于非生长季节 CO 排放如何响应退化（特别是由高原鼢鼠加剧的退化），人们知之甚少，因为大多数先前的研究主要集中在生长季节。在这项研究中，在对比的气候条件下（2013-2014 年的正常季节和 2014-2015 年的“温暖和湿润”季节），通过四个退化水平（即健康草地（HM）、退化斑块（DP）、两年鼢鼠丘（ZM2）和当年鼢鼠丘（ZM1））来研究 CO 排放和相应的环境和农学变量的影响。非生长季节 CO 排放的时间变化主要受土壤温度调节，而随着退化程度的增加，由于土壤水分含量的减少，降低了 CO 排放的温度敏感性。整个非生长季节的 CO 累积排放量为 587-1283kg C ha-1，所有退化水平之间存在显著差异（p < 0.05）。高山草甸的退化显著降低了植被覆盖度、地上净初级生产力和地下生物量，这通常被认为会减少土壤 CO 排放。然而，在 2014-2015 年的温暖和湿润季节，退化草地的非生长季节 CO 排放（按 DP、ZM2 和 ZM1 的面积加权）估计为 641-1280kg C ha-1，与 2013-2014 年的正常季节相比，这一排放显著更高（p < 0.05）。此外，草地退化大大增加了生产力标准化的非生长季节 CO 排放，这与退化程度呈指数增长趋势。这些结果表明，草地退化与土壤碳损失之间存在很强的联系，例如以 CO 释放的形式，这表明迫切需要管理退化草地的恢复，以有助于减缓气候变化。
