青海湖北岸草甸草原CO_(2)通量年际动态及其驱动机制

Interannual dynamics and driving mechanism of CO_(2) flux in meadow grassland on the north shore of Qinghai Lake

青藏高原草甸草原是生态系统中重要的植被类型,准确评估高寒草甸草原生态系统碳源汇状况及碳储量变化尤为重要。基于涡度相关系统观测,分析了2009年至2016年8年期间青海湖北岸草甸草原环境因子以及碳通量的变化特征,运用结构方程模型(SEM)分析环境因子对总初级生产力(GPP)、净生态系统CO_(2)交换量(NEE)、生态系统呼吸(Re)的调控机制。结果表明:2009—2016年8年NEE日均值在-2.02—0.88 gC m^(-2)d^(-1)之间,5—9月NEE为负值,表现为碳吸收,雨热同期的6、7、8月是CO_(2)净吸收最强的时期,平均每月吸收CO_(2)39.85 gC m^(-2)month^(-1),NEE负值日数约占全年的48%,10月—翌年4月为正值,表现为碳释放,初春3月和秋末11月是CO_(2)净释放最强的时期;Re日均值为1.69 gC m^(-2)d^(-1),受季节温度的影响,呈夏季强,冬季弱的态势,夏季的生态系统呼吸强度大约是冬季的8倍,秋季较春季呼吸强度更大;GPP日均值为3.15 gC m^(-2)d^(-1),随着光照辐射强度不断增大,生长季的光合生产能力显著强于非生长季,夏季最强,秋季较春季更强。从年际尺度分析可得研究区为一碳汇区,8年平均碳吸收强度为63.51 gC m^(-2)a^(-1),2015年碳吸收最强NEE为-95.80 gC m^(-2)a^(-1),2016年碳吸收最弱NEE为-30.60 gC m^(-2)a^(-1)。通过SEM分析可得:气温(Ta)对Re和GPP有显著提高的作用,GPP对NEE有极显著负响应,而Re对NEE有极显著提高作用。暗示在气候变暖的背景下,未来气温升高,青海湖北岸草甸草原生态系统碳汇功能可能会加强。

The Qinghai-Tibet Plateau meadow steppe is an important vegetation type in the ecosystem.It is particularly important to accurately assess the carbon source-sink status and carbon storage changes of the alpine meadow-steppe ecosystem.Based on the observation of eddy correlation system,the change characteristics of environmental factors and carbon flux in the meadow steppe on the north bank of Qinghai Lake from 2009 to 2016 were analyzed.The structural equation model(SEM)was used to analyze the regulatory mechanism of environmental factors on total primary productivity(GPP),net CO_(2)exchange capacity(NEE)and respiration(Re).The results showed that the daily mean value of NEE from 2009 to 2016 ranged from-2.02 to 0.88 gC m^(-2)d^(-1),and NEE was negative from May to September,representing carbon absorption.The net absorption of CO_(2)in June,July and August of rain-hot period was the strongest,with the average absorption of CO_(2)of 39.85 gC m^(-2)month^(-1)per month,the number of NEE negative days accounted for about 48%of the whole year.It was positive from October to April of the next year,showing carbon release.The net CO_(2)release was the strongest in early spring,March and late autumn,November.The daily mean value of Re was 1.69 gC m^(-2)d^(-1),which was strong in summer and weak in winter due to the influence of seasonal temperature.The ecosystem respiration intensity in summer was about 8 times that in winter,and the intensity in autumn was higher than that in spring.The daily average of GPP was 3.15 gC m^(-2)d^(-1).With the increasing of light radiation intensity,the photosynthetic productivity in growing season was significantly stronger than that in non-growing season,while it was strongest in summer and stronger in autumn than in spring.According to the interannual scale analysis,the study area was a carbon sink area,and the average carbon absorption intensity in 8 years was 63.51 gC m^(-2)a^(-1),the highest NEE of carbon absorption in 2015 was-95.80 gC m^(-2)a^(-1),and the lowest NEE of carbon absorption in 2016 was-30.60 gC m^(-2)a^(-1).SEM analysis showed that air temperature(Ta)significantly improved Re and GPP,GPP had a very significantly negative response to NEE,and Re had a very significant improvement to NEE.It is suggested that under the background of climate warming and future temperature rise,the carbon sink function of meadow grassland ecosystem in the north bank of Qinghai Lake may be strengthened.