科尔沁草甸生态系统净碳交换特征及其驱动因子

Net ecosystem carbon exchange and its main driving factors in meadow grassland ecosystems in the Horqin Sand Lands

以2013年10月-2014年9月连续观测的CO2 通量数据为基础,分析了科尔沁草甸生态系统净碳交换量（NEE）的时间变化特征及其驱动因素.结果表明,NEE 日变化季节差异明显,生长季变化幅度大,净CO2 日吸收速率7月〉8月〉9月〉6月〉5月;生长季内,NEE 主要受控于叶面积指数和光合有效辐射.NEE 与光合有效辐射（PAR）之间的关系可用直角双曲线方程来描述,拟合得到的表观初始光能利用率α为0.0015μmolCO2/μmolPAR,最大光合速率Pmax为0.65μmolCO2/（m^2·s）.叶面积指数（LAI）对NEE 的影响可由分段函数表示,当LAI〉3.08时,表现为渐进饱和型,且LAI越大NEE 对PAR 的响应越明显;当高饱和水汽压差（VPD）在1.5～2.0kPa时,光合作用开始降低,NEE 明显受到VPD 值的抑制;短暂强降雨（累计降雨量〉40 mm/d）对昼间NEE 有一定的抑制,而持续低强度降雨（降雨时长〉15h）对夜间NEE 存在激发作用;夜间NEE 随土壤温度呈指数增长,温度敏感系数（Q10）为2.63.

The objectives of this study were to investigate the main drivers of ecosystem carbon dynamics in meadow grasslands in the Horqin Sand Lands,and to understand the relationship between net ecosystem CO2 exchange (NEE)and key meteorological factors in this region.We continuously measured (NEE)and environ-mental factors in meadow grasslands in the Horqin Sand Lands from October 2013 to September 2014 using the eddy covariance method.The results showed that the diurnal variation in NEE differed significantly among sea-sons,especially among vegetation growing seasons.The highest seasonal diurnal absorption rate of CO2 was in July,followed by August,September,June,and then May.The NEE was controlled by photosynthetically ac-tive radiation (PAR)and the leaf area index (LAI)during vegetation growing seasons.The relationship be-tween NEE and PAR was expressed by a rectangular hyperbolic function.The simulated apparent initial aver-age light-use efficiency was 0.0015 μmol CO2/μmol PAR,and the maximum photosynthetic rate (P max )was 0.65 μmol CO2/(m2 ·s).The NEE was influenced by LAI,which was expressed by piecewise functions.When the LAI was greater than 3.08,NEE-PAR showed a gradual saturation-type relationship.The higher the LAI,the stronger the response of net carbon exchange to the amount of PAR.A light saturation response occurred when 1.5<VPD<2 kPa,and NEE was significantly inhibited under high VPD.The day-time net CO2 exchange was inhibited by heavy rainfall (cumulative rainfall>40 mm/day),while sustained low-intensity rain-fall (rainfall length>15 h)stimulated soil respiration at night.The night-time respiration rate of the ecosystem (R eco )increased exponentially as the soil temperature (T s )increased,and the temperature-sensitive coefficient Q10 was 2.63.