青海湖北岸高寒草甸草原生态系统CO_2通量特征及其驱动因子

CO_2 fluxes and their driving factors over alpine meadow grassland ecosystems in the northern shore of Qinghai Lake,China

草甸草原是青藏高原的重要植被类型,与其他植被类型相比,其碳交换过程和驱动机理的研究仍较薄弱。利用青海湖东北岸草甸草原的涡度相关系统观测的连续数据(2010年7月1日-2011年6月30日),分析了草甸草原CO2通量特征及其驱动因子。结果表明:草甸草原净生态系统CO2交换量(NEE)在植物生长季的5-9月,其日变化主要受控于光合光量子通量密度(PPFD);而非生长季(10月21日-4月19日)和生长季初(4月下旬)、末期(10月中上旬)NEE的日变化主要受气温(Ta)的影响。CO2日最大吸收值和释放值分别出现在7月1日(11.37gCO2·m-2·d-1)和10月21日(4.04gCO2·m-2·d-1)。逐日NEE主要受控于Ta,两者关系可用指数线性(explinear)方程表示(R2=0.54,p<0.01)。叶面积指数(LAI)和增强型植被指数(EVI)对逐日NEE的影响表现为渐近饱和型,LAI和Ta交互作用明显(p<0.05),EVI的主效应强烈(p<0.001)。生态系统的呼吸熵(Q10)为2.42,总呼吸(Reco)约占总初级生产力(GPP)的74%。生长季适度的昼夜温差(<14.8℃)有利于系统的碳蓄积。研究时段该草甸草原作为碳汇从大气吸收271.31gCO2·m-2。

Aims Meadow grassland is a dominant vegetation type on the Qinghai-Tibetan Plateau,but its mechanisms con-trolling the exchange of CO2 across a spectrum of time scales and carbon budget remain unclear.Our objective was to investigate the main drivers of ecosystem carbon dynamics and understand the potential response to future climate warming.Methods We used the eddy covariance method for continuously measuring net ecosystem CO2 exchange（NEE） and environmental factors over meadow grassland on the northern shore of Qinghai Lake from July 1,2010 to June 30,2011.Important findings Diurnal changes of NEE were controlled by photosynthetic photon flux density（PPFD）dur-ing the middle growing season（May to September）,and air temperature（Ta）was the determining factor on diurnal NEE during other periods.The maximum daily CO2 uptake and release rate were 11.37 g CO2·m-2 ·d-1 on July 1 and 4.04 g CO2·m-2 ·d-1 on October 21,respectively.Ta was the primary environmental factor related to daily NEE,and the correlation was described by an exponential-linear equation（R 2 =0.54,p0.01）.A significant asymptotical response of daily NEE with increasing leaf area index（LAI）and enhanced vegetation index（EVI） was observed.The interaction effect of LAI and Ta was significant（p〈0.05）,while main effect of EVI versus Ta was more important（p〈0.001）.Respiration quotient（Q10）was 2.42 and ecosystem total respiration（Reco）consumed 74%of gross primary production（GPP）.The proper magnitude of diurnal temperature range（14.8 ℃）could be propitious to ecosystem carbon sequestration.The meadow grassland acted as carbon sink and ab-sorbed 271.31 g CO2·m-2 from the atmosphere during the study period.