云贵高原草地生态系统CO2通量变化特征

草地是云贵高原的重要植被类型,与其他地区研究相比,该地区草地生态系统的CO₂交换过程和驱动机理的研究较为薄弱。基于涡度相关系统对云贵高原草地生态系统观测的连续高频数据(2017年10月-2018年8月),分析了该生态系统CO₂通量的时间变化特征及其环境影响因素。结果表明:日尺度上CO₂通量具有显著的变化特征,为明显的单峰型变化,白天净吸收,夜晚净排放。季节尺度上,每月均为碳吸收,吸收速率呈春夏高,秋冬低的特征,吸收峰值出现在6月,最低值在1月,且生长季的碳吸收变化幅度比非生长季大。影响CO₂通量变化的主要环境因子有太阳辐射、气温、土壤温度和风速,综上,云贵高原草地生态系统CO₂通量对温度较为敏感,温度升高可提高其固碳能力。总的来看,该生态系统是一个明显的碳汇,研究时段内净碳吸收量为425.14 g CO₂·m^-2。

Factors influencing CO2 fluxes of a grassland ecosystem on the Yunnan-Guizhou Plateau,China

Grassland is a dominant vegetation type on the Yunnan-Guizhou Plateau, and comparatively little is known about the CO₂ flux and its diurnal and seasonal variation. Based on in-situ measurement using eddy covariance methodology from October 2017 to August 2018, the diurnal cycle and seasonal variations of CO₂ flux for a grassland ecosystem of Yunnan-Guizhou Plateau were analyzed, and key factors determining CO₂ flux were determined. The CO₂ flux had obvious diurnal variation, with net uptake during the day and net emission at night, and the diurnal cycle being more significant in growing season than in the non-growing season. Overall, the grassland ecosystem was a sink of atmospheric CO₂, which also varied seasonally with high uptake rate in spring and summer and low rate in autumn and winter. Specifically, the peak CO₂ uptake rate occurred in June and lowest was observed in January. The diurnal and seasonal variation in the CO₂ flux were associated with solar radiation, air temperature, soil temperature and wind speed fluctuations. Global warming would enhance the carbon sequestration capacity of the grassland ecosystem, given the CO₂ flux was sensitive to temperature. Our results suggested that the grassland ecosystem acted as carbon sink and absorbed 425.14 g CO₂·m^-2 from the atmosphere during the study period.