短花针茅荒漠草原生态系统净碳交换对载畜率的响应

摘要

草地生态系统作为中国最大的陆地生态系统,其碳循环的动态变化在全球碳收支平衡中扮演着重要角色.为探讨短花针茅(Stipa breviflora)荒漠草原净CO2交换的日变化和季节变化特征,阐明放牧及土壤温度和湿度的季节性变化对生态系统净CO2交换的影响,采用便携式光合仪LI-6400(LI-COR,USA)和密闭式箱法于2013—2014年生长季(5—10月)测定了对照(CK)、轻牧(LG)、中牧(MG)和重度放牧(HG)4个处理的生态系统净碳交换.结果表明:短花针茅荒漠草原净 CO2交换具有明显的日变化规律.净碳交换的日动态主要受气温影响,昼间净碳吸收随温度升高而降低,甚至出现碳释放;夜间随气温降低,生态系统呼吸减弱.整个生长季,短花针茅荒漠草原表现为碳汇,在植物生长季的高峰期,净碳吸收达到峰值(-2.96 mol·m-2·s-1).年际间生态系统净碳交换差异显著(P<0.0001),净碳交换主要受降水调控.净碳吸收与土壤温度在两年间均呈显著的二次多项式关系(P<0.01),而与土壤湿度的关系则是2013年为显著的线性关系(P<0.0001), 2014年为显著的二次多项式关系(P<0.01).土壤温度对生态系统净 CO2交换变化的解释能力为0.31~0.36,而土壤湿度对生态系统净CO2交换变化的解释能力为0.26~0.51.HG区净碳吸收速率(-0.66 mol·m-2·s-1)显著低于CK区(-1.65 mol·m-2·s-1).放牧减弱了荒漠草原的固碳潜力.%To explore the diurnal and seasonal dynamics of net CO2exchange characteristics of Stipa Breviflora desert steppe,and to clarify the effects of grazing and seasonal variations of soil temperature and moisture on net ecosystem CO2exchange, we used portable optical LI-6400 (LI-COR, USA) and the method of static chamber to measure net ecosystem carbon exchange under the four stocking rate treatments (control-CK, lightly grazing-LG, moderately grazing-MG, heavily grazing-HG) during the growing season (from May to October) of 2013 and 2014. During this period, we also measured soil temperature and soil moisture at a depth of 10 cm twice per month. Diurnal dynamics of net carbon exchange was measured once per month in July and August on sunny days. We found that the diurnal dynamics of net CO2exchange of Stipa breviflora desert steppe was related to air temperature.During the day, net carbon absorption decreased with increasing temperature, and even carbon release occurred. As the temperature decreased at night,ecosystem respiration decreased.Throughout the growing season,Stipa breviflora desert steppe acted as carbon source,only moderately and heavily grazing plots had a slight carbon release in June. When biomass reached peak, net carbon gain was the highest (-2.96 mol·m-2·s-1). Year significantly affected net ecosystem CO2uptake (P<0.000 1). Net carbon exchange was mainly controlled by precipitation. There was a significant quadratic polynomial relationship between net CO2exchange and soil temperature in 2013 and 2014 (P<0.01). A significant linear relationship was found between net CO2exchange and soil moisture in 2013 (P<0.000 1), and a significant quadratic polynomial relationship in 2014 (P<0.01). The influence of soil temperature soil temperature on net ecosystem CO2exchange was 0.31~0.36, while soil moisture on the change of net ecosystem CO2exchange was 0.26~0.51. The net carbon uptake rate in HG block (-0.66 mol·m-2·s-1) was significantly lower than that in CK block (-1.65 mol·m-2·s-1). Therefore, grazing can reduce carbon sequestration potential of desert steppe.