Net primary productivity (NPP) is one of the core components of the grassland wetland ecosystem carbon balance and climate change. Based on data of vegetation index, meteorology (precipitation and temperature), and vegetation type, we used the CASA (Carnegie-Ames-Stanford Approach) model to estimate NPP of the Zoige grassland wetland from 1999 to 2015. The spatial and temporal patterns of NPP in the Zoige grassland wetland ecological function area and its relationship with precipitation and temperature were examined. The results showed that the measured values of NPP were close to the simulated values, with the root mean square error being 120.3 g C·m-2 and a R2 of 0.78. The annual mean and the growth season (April-September) mean of NPP of the study area were 329.0 and 229.4 g C·m-2·a-1, respectively, with obvious inter-annual fluctuations, with a weak trend of decline (2.3, 1.6 g C·m-2·a-1). The inter-annual fluctuations of NPP in different vegetation types were basically consistent with the overall fluctuations of NPP of the whole study area. The slope of NPP in annual and growing seasons was from -21.3 to 18.7, -31.5 to 23.1 g C·m-2·a-1. The area with significant increase (mainly distributed in forest coverage area and wetland ecological compensation area) only accouned for 0.3% and 0.7% of the total area, and the area with significant decline (mainly distributed in areas where human activities were concentrated) only accounted for 1.4% and 6.4% of the total area, respectively. The carbon sequestration capacity of different vegetation types was different, among which the forest was the strongest, the grassland was the second, and the wetland vegetation was the weakest. Precipitation was the dominant climatic factor affecting NPP in grassland wetland.
植被净初级生产力(NPP)是草原湿地生态系统碳收支平衡和气候变化的核心内容之一。本研究基于植被指数、气象数据(降水和气温)、植被类型数据,利用CASA模型对若尔盖草原湿地1999—2015年NPP进行估算,分析了若尔盖草原湿地NPP时空格局特征及其与气候因子的关系。结果表明: NPP实测值与模拟值之间显著相关,R2为0.78,均方根误差为120.3 g C·m-2·a-1;研究区年均和生长季(4—9月)NPP分别为329.0、229.4 g C·m-2·a-1,年际间波动明显,以2.3、1.6 g C·m-2·a-1的微弱趋势下降,不同植被类型的年均及生长季NPP的年际波动与整个研究区的波动趋势基本一致;年均和生长季NPP的变化斜率分别为-21.3～18.7、-31.5～23.1 g C·m-2·a-1,显著增加的面积分别占研究区总面积的0.3%和0.7%,主要分布于森林覆盖区和湿地生态补偿区;显著下降的面积分别占研究区总面积的1.4%和6.4%,主要分布于人类活动集中的地区;研究区不同植被的固碳能力存在差异,其中,森林最强,草地次之,湿地最弱;降水是影响草原湿地植被NPP的主导气候因子。.
Keywords: Zoige; climate response; net primary productivity (NPP); spatio-temporal variation characteristics.