1982-2010年中国草地净初级生产力时空动态及其与气候因子的关系

植被净初级生产力（NPP）及其与气候变化的响应研究是全球变化的核心内容之一。论文基于长时间序列遥感数据和气象数据，通过光能利用率模型（Carnegie-Ames-Stanford approach， CASA模型）模拟了1982-2010 年中国草地NPP，进而分析其时空变化特征及其与气候水热因子的相关性。结果表明：（1）1982-2010年中国草地年平均NPP为282.0 gC m^-2a^-1，年总NPP的多年平均值为988.3 TgC；空间分布上呈现东南部高西北部低的特征。（2）近30年中国草地NPP增加速率为0.6 gC m^-2a^-1，呈增加趋势的面积占中国草地总面积的67.2%；总体上，中国草地NPP呈极显著和显著增加的比例（35.8%、8.0%）大于呈极显著和显著减少的比例（5.8%、4.8%）；NPP明显增加的区域主要包括青藏高原西部、阿拉善高原、新疆西部；明显降低的区域主要分布在内蒙古地区；不同年代际和不同草地类型的NPP变化趋势差异明显。（3）草地NPP与降水量的相关性高于与温度的相关性。不同草地类型NPP对气温、降水量的响应程度不同，其中温性荒漠草原 、温性草原、温性草甸草原的NPP与降水量均达到显著正相关（P<0.05）。

Spatio-temporal dynamics of grassland net primary productivity and their relationship with climatic factors from 1982 to 2010 in China

Global warming has led to significant vegetation changes in the past half century. Grasslands in China are mainly located in ecologically fragile regions, which are sensitive to climate change. During recent decades, grasslands have experienced prominent warming and drying. Therefore, investigating the response of grasslands to climatic variations is necessary for a better understanding of the cumulative consequences of climate change. Grassland net primary productivity (NPP) is an important indicator for evaluating grassland ecosystem conditions. We used multi-source remote-sensing data and meteorological data to estimate the grassland NPP from 1982 to 2010, based on the Carnegie-Ames-Stanford approach (CASA) model. The spatial pattern and change trends of grassland NPP were evaluated. The response of grassland NPP changes to climatic variations was also analyzed. The results revealed that the spatial distribution of grassland NPP showed an increasing trend from the northwest to southeast across China. During the period from 1982 to 2010, the grassland mean NPP was 282 gC m^-2a^-1, and NPP exhibited apparent spatial heterogeneity, being highest (710 gC m^-2a^-1) in the dry heat savanna shrub and grass and lowest (58 gC m^-2a^-1) in the alpine desert. The total annual NPP was 988.3 Tg C. Grassland NPP has increased slightly in the past 30 years, at a rate of 0.6 gC m^-2a^-1. Regions showing increasing NPP accounted for 67.2% of the total grassland areas, within which, areas with extremely significant (P<0.01) and significant (P<0.05) increases accounted for 35.8% and 8.0% of the total grassland area, respectively. Regions showing extremely significant and significant decreases encompassed only 5.8% and 4.8% of total grassland area, respectively. Clear increases in grassland NPP were observed in the west of the Qinghai-Tibet Plateau, the Alxa Plateau and western area of Xinjiang. Areas with a decrease in grassland NPP were mainly distributed in the western regions of Inner Mongolia. Furthermore, the increasing rate of NPP showed temporal variation and differed among different grassland types. The correlation coefficient between NPP and precipitation was larger than that between NPP and temperature. Moreover, the response of grassland NPP to temperature and precipitation differed for different grassland types. There were significant positive correlations between annual precipitation and NPP in temperate desert steppe, temperate steppe, and temperate meadow steppe.