Abstract: Using the improved CASA model based on comprehensive and sequential classification system of grasslands (CSCS),the grassland net primary productivity(NPP)from 2004 to 2008 in China and its spatio-temporal variations were estimated and analyzed. The results showed that from 2004 to 2008,the annual average value is 489.4 g C·m^-2·a^-1. The grassland NPP in China from 2004 to 2008 followed an overall trend of increase. From the trend of monthly variation,it can be drawn that the NPP accumulative period was mainly between April and October when the combination of water and thermal is in a good condition for grassland vegetation growth. The sum of the NPP in these seven months was about 89.1% of the annual total. The grassland NPP in spring,summer,autumn and winter was about 18.6%,59.6%,17.4% and 4.5% of the total annual NPP respectively. According to the annual,monthly and seasonal variation of grassland vegetation NPP,the suitable combination of water and thermal plays key roles in grassland vegetation growth. The grassland NPP increased with the increasing longitude and the decreasing latitude,although there were some fluctuations. The characteristic of longitude and latitude zonation of grassland NPP had a high correlation with zonal regularity of water and thermal.

Key words: Comprehensive and sequential classification system of grasslands (CSCS), Grassland net primary productivity, Spatio-temporal distribution

摘要： 利用基于草原综合顺序分类系统（CSCS）的改进CASA模型，估算2004-2008年中国草地净初级生产力并分析其时空分布特征。结果表明：2004-2008年中国草地NPP年平均为489.4 g C·m^-2·a^-1，5年里草地NPP总体呈现增加趋势。草地NPP的积累期主要发生在水、热搭配较好的4-10月，占了全年总量的89.1%。春（3月-5月）、夏（6月-8月）、秋（9月-11月）、冬（12月-2月）四季的草地NPP各自占全年总量的18.6%，59.6%，17.4%和4.5%。由年际、月份—空间和季节—空间的NPP变化可知，适宜的水热搭配是草地NPP积累的关键。中国草地NPP随经度的递增而逐渐增大，随纬度的增大而逐渐减小，但存在一定的波动性，其变化规律与水、热状况的地带性规律相一致。

关键词: 草原综合顺序分类系统, 改进CASA模型, 草地净初级生产力, 时空分布