新疆北部覆膜滴灌棉田的碳交换日、生长季变化特征

利用涡动相关系统测定新疆石河子棉区覆膜滴灌棉田的CO₂通量，分析2010年棉花各生育期净生态系统碳交换（NEE）的日变化特征，并将NEE]拆分为生态系统总生产力（GEP）和生态系统呼吸（R_eco），分析三者的生长季变化特征及其影响因素。结果表明：在播种期和苗期，棉田白天和夜间的NEE变化幅度都较小；其他生育期NEE白天呈‘V’形变化，夜间为正值且变化小。NEE的日变化主要受太阳总辐射影响。GEP、R_eco和NEE的生长季变化趋势与叶面积指数变化相对一致，最大日累积量均出现在花铃期，分别为11.8，8.0和-6.2 g C·m^-2·d^-1。播种期、苗期、蕾期、花铃期和吐絮期的日平均NEE]分别为2.6，1.6，-1.2，-2.8和0.5 g C·m^-2·d^-1。整个生长季棉田NEE累积量为-122.2 g C·m^-2，表现为碳汇。由偏相关分析可得，GEP，R_eco和NEE的生长季变化与气温的相关系数最高，其次为饱和水汽压差，再次为太阳总辐射和土壤温度，结果表明气温是影响棉田GEP，R_eco和NEE生长季变化的主要气象因素。气温对棉田GEP，R_eco和净碳吸收起促进作用，而饱和水汽压差对其起限制作用。

Diurnal and seasonal variation of carbon dioxide exchange over a film-mulched cotton field under drip irrigation in northern Xinjiang

To study the diurnal and seasonal variation of CO₂ fluxes and to explore the effects of biotic and abiotic factors on the seasonal dynamics of CO₂ exchange for cotton fields，CO₂ fluxes were measured using Eddy covariance （EC） methods at a film-mulched cotton field under drip irrigation in Wulanwusu （85°49′E，44°17′N，469 m a. s. l.），which is located in northern Xinjiang in the northwest part of China and has a continental climate. The net ecosystem carbon exchange （NEE） was partitioned into gross ecosystem production （GEP） and ecosystem respiration （R_eco）. Diurnal changes of NEE in each growth stage and evolution of daily GEP，R_eco and NEE in cotton growing season were analyzed. Except for the emergence and seedling stage，the daytime CO₂ fluxes varied with maximum assimilation occurred closing to the noon while the nighttime fluxes changed little. Overall，the evolution of daily GEP，R_eco and NEE was closely related to the leaf area index （LAI）. Absolute values of GEP，R_eco and NEE increased to the maximum of 11.8，8.0 and 6.2 g C·m^-2·d^-1 respectively in the flower-boll stage when the LAI reached peak. The mean daily NEE was 2.6，1.6，-1.2，-2.8 and 0.5 g C·m^-2·d^-1 for the emergence，seedling，squaring，flower-boll and boll-opening stage，respectively. The integrated NEE value for the whole growing season was about -122.2 g C/m² and for the whole year of 2010 was 65 g C·m^-2·a^-1，showed that the cotton fields behaved as a carbon sink in growing season and weak carbon source for the year. Partial correlation coefficients between daily CO₂ fluxes and meteorological factors showed that air temperature was the most important one influencing the dynamics of carbon fluxes during the growing season. The rise in air temperature increased assimilation of carbon dioxide while vapor pressure deficit （VPD） exerted significant limitation on the carbon fluxes.