2001—2010年中国农田生态系统NPP的时空演变

植被净初级生产力(Net Primary Productivity,NPP)是地表碳循环的重要组成部分,而农业NPP代表了农田生态系统通过光合作用可固定大气中CO2的能力,决定了农田土壤可获得的有机碳含量.测算中国农田生态系统产生的NPP并分析其时空变异规律,探索其影响因子,对于了解全球碳循环,预测未来生态变化趋势具有重要意义.基于MOD17A3数据集,利用一元线性回归趋势线法和相关系数法定量分析了农田生态系统NPP的时空演变特征和气候因子对农田NPP的影响.结果表明,2001-2010年中国农田NPP平均值变化范围为C 0.21 ～ 17.24 Mg hm-2a-1,平均值为4.12 Mg hm-2 a-1.从时间变化来看,NPP年际变化呈现先增加后下降的趋势.从空间分布来看,表现为南方高,北方低,其中,甘新区、黄土高原区、东北区、内蒙古及长城沿线区和黄淮海区北部NPP值较低,＜3 Mg hm-2 a-1;四川盆地、山东丘陵、长江中下游滨海和沿江平原、云南、贵州、海南等地NPP值较高,＞5 Mghm-2 a-1.从变化趋势来看,黄淮海农业区、黄土高原区、新疆的绿洲农业区和长江中下游农业区南部上升趋势明显,东北农业区、四川盆地和长江中下游农业区下降趋势明显.2001-2010年,中国农田中有22％的像元NPP平均值与降水呈显著相关,7％的像元与气温呈显著相关,反映了农田生态系统受人类活动影响较大.

Spatio-temporal Variation of NPP in Cropland Ecosystem of China during the Years From 2001 to 2010

Objective] Net primary productivity (NPP) of vegetation is an important part of the land surface carbon cycle and is closely related to the processes of carbon recycling and global climate change.NPP of agricultural vegetation represents capacity of the agroecosystem fixing CO2 from the atmosphere via photosynthesis,and determines how much organic carbon the agricultural soil can sequestrate.Agricultural soil is a huge carbon (C) pool.An accurate estimation of how much carbon can be turned into organic matter may help better understand the mechanism of carbon recycling in farmland soil,predict which way carbon tends to go in recycling and manage carbon recycling in farmland soil.China is a country vast in territory,changeable in climate,complex in type of regions,and diverse in agricultural pattern,making the farmland ecosystems,one of the sectors the most sensitive to global climate change.Size and variation of the agricultural carbon pool is very important to both the world's food safety and global carbon balance.It is,therefore,of important significance to understanding of the role of China in global carbon recycling and prediction of future trend of the global climate change,to accurately estimate NPP of the farmland ecosystem of China,analyze its spatio-temporal variation rules and explore for its affecting factors Method] In this study,based on the annual net primary productivity (NPP) data cited from the MOD17A3 dataset,characteristics of the spatial-temporal variation of NPP of the farmland in China and impacts of climatic factors on farmland NPP were analyzed quantitatively with the single factor linear regression trendline method and correlation coefficient method.Result] Results show that during the years from 2001 to 2010,the annual NPPs averaged to be C 4.12Mg hm-2 a-1,ranging from 0.21 to 17.24 Mg hm-2 a-1.Within this period of time,annual NPP rose first and then declined,and within the territory of China,the Gansu-Xinjiang Region,the Loess Plateau Region,Northeast China,Inner Mongolia,areas alongside the Great Wall and northern part of the Huang-Huai-Hai Region were quite low in NPP,and even lower than 3 Mg hm-2 a-1,whereas the Sichuan Basin,Shandong Hilly Region,the coastal areas of East China and areas alongside the Middle Lower Reaches of the Yangtze River,Yunnan,Guizhou and Hainan were quite high,and even going beyond 5 Mg hm-2 a-1.In about 55％ of the pixels NPP displayed a rising trend,especially in the pixels representing the Huang-Huai-Hai Agricultural Region,the Loess Plateau Region,oasis agricultural areas in Xinjiang,and the south part of the agricultural region of the Middle-Lower Reaches of the Yangtze River.But NPP in Northeast China agricultural zones,Sichuan Basin and most part of the agricultural region of the Middle Lower Reaches of the Yangtze River displayed reversely.In order to assess the impact of climate factors on crop NPP in China,we analyzed relationships between average NPP and mean temperature and precipitation during the years of 2001-2010.It was found that average NPP was significantly related to precipitation in about 22％ of the pixels of the farmland of China,and with temperature in about 7％ of the pixels,which indicates that the agroecosystem of China is greatly affected by human activities such as tillage and farming pattern,cropping system and field management.Conclusion] Farmland NPP of China varied sharply in space.It was relatively low in the north and quite high in the south,but displayed a rising trend in most parts of the country.However,its spatial distribution did not tally with its variation trend.In areas that used to be low in NPP,a rising trend was observed with NPP,and vice versa.The agroecosystem of China was less affected by climatic factors than by human activities.It is,therefore,advisable to pay more attention to quantification of the factors of human activities in future studies on influential factors of the agroecosystem.