青藏高原高寒草甸和荒漠碳交换特征及其气象影响机制

Carbon exchange characteristics and meteorological influence mechanism of Alpine Meadow and Desert in Qinghai-Tibet Plateau

以青藏高原玛沁地区高寒草甸和沱沱河地区高寒荒漠草原为观测研究站,利用涡动协方差技术获取高寒生态系统水平上的CO_(2)通量以及水和能量通量,通过REddyProc、随机森林(Random Forest,RF)进行了数据后处理,探究了不同下垫面典型环境因子对净生态系统CO_(2)交换量(Net Ecosystem Exchange,NEE)的影响机制。结果表明:1)玛沁高寒草甸在6—7月以吸收为主,表现为碳汇,吸收峰值出现在11:00—12:00(北京时,下同)之间,而在3、4、5、8月以排放为主,表现为碳源,排放峰值出现在21:00—23:00之间;沱沱河高寒荒漠在3—8月以吸收为主,表现为净碳汇,吸收峰值出现在13:00—14:00之间;整个生长季前后(3—8月),玛沁和沱沱河的累计NEE分别为79.50 g C/m^(2)和79.24 g C/m^(2),都表现为碳汇。2)不同尺度不同下垫面,气象因子对NEE的重要程度不同,小时尺度上,高寒草甸辐射对NEE的重要性最大,高寒荒漠草原蒸散发对NEE的重要性最大;日尺度上,高寒草甸土壤含水率对NEE的重要性最大,高寒荒漠草原风速对NEE的重要性最大;3)生态系统呼吸(Ecosystem Respiration,Reco)和NEE都受到总初级生产力(Gross Primary Productivity,GPP)的显著限制,高寒荒漠草原GPP对NEE的影响远大于高寒草甸GPP对NEE的影响;4)NEE与蒸散发呈显著相关性,表明水分条件是控制高寒草甸和高寒荒漠草原碳和水收支变化的最重要因素。

In this study,the alpine meadow in Maqin area of Qinghai-Tibet Plateau and the alpine desert steppe in Tuotuo Rivers area were taken as the observation stations.The eddy covariance technique was used to obtain the CO_(2)flux,water and energy flux at the level of alpine ecosystem.The data were post-processed by REddyProc and Random Forest(RF),and the variation characteristics of Net Ecosystem Exchange(NEE)at different time scales and different underlying surfaces were analyzed,so as to accurately evaluate and compare the carbon budget under different underlying surfaces.The influence mechanism of meteorological factors on CO_(2)flux of alpine meadow and alpine desert grassland was explored,which provided reference and data support for the research on carbon and water cycle of alpine meadow and alpine desert grassland in Qinghai-Tibet Plateau.The results showed that:1)Maqin alpine meadow mainly absorbed carbon sink from June to July,and the absorption peak appeared between 11:00 and 12:00(Beijing,the same below).However,in March,April,May and August,the main emission was carbon source,and the emission peak appeared between 21:00 and 23:00.The alpine desert of Tuotuo Rivers was mainly absorbed from March to August,showing net carbon sink,and the absorption peak appeared between 13:00 and 14:00;around the whole growing season(March—August),the cumulative NEE of Maqin and Tuotuo Rivers were 79.50 g C/m^(2)and 79.24 g C/m^(2),respectively,showing carbon sink.2).The correlation between carbon flux and meteorological factors was different in different scales and underlying surfaces.On the hourly scale,the importance of alpine meadow radiation(Rg)to carbon flux was the largest.Evapotranspiration(ET)in alpine desert steppe was the most important factor for carbon flux.On the daily scale,soil water content(Soil_VWC)was the most important factor for carbon flux in alpine meadow,while wind speed(WS)was the most important factor for carbon flux in alpine desert steppe.3)Ecosystem Respiration(Reco)and Net Ecosystem Exchange(NEE)were significantly restricted by total primary productivity(GPP),and 91%of the GPP contributed to Reco and 9%to NEE;in alpine desert steppe,40%of the GPP contributed to Reco and 60%to NEE.4)NEE was significantly correlated with ET,indicating that water condition was the most important factor controlling the changes of carbon and water budget in alpine meadow and alpine desert steppe.5)Human activities intensified the impact of climate change and the susceptibility of carbon balance,and became the inducing factors of weak carbon sources in March,April,May and August in Maqin.