Spatio-temporal Variation Of NPP And Its Climate Factors In Cropland Ecosystem Of Fujian Province During The Year From 2000 To 2014

Net Primary Productivity(NPP)is an important part of surface carbon cycle,and the carbon cycle of farmland ecosystem is the most active part of the global carbon pool.Agricultural vegetation NPP represents the ability of the farmland ecosystem fixing CO2 in the atmosphere by photosynthesis,which can reflect ecosystem productivity as the scale of the unified standard,and it is a good measure farmland productivity.The study of the spatial and temporal evolution characteristics and influencing factors of NPP in farmland ecosystem not only helps us to understand farmland productivity,but also provides scientific basis for assessing the safety of cultivated land resources and food security.We Based on cropland of Fujian province,using he MOD 17A3H data set during the years of 2000-2014 from EOS/MODIS satellite and the data of combination with solar radiation,air temperature and precipitation were used in this paper.Spatial and temporal evolution characteristics of cropland NPP during the years of 2000-20 and its correlation with climate factors were analyzed on regional and pixel with the methods of anomaly analysis,trend analysis and correlation analysis.The main conclusions are as follows:(1)During the yearfrom 2000 to 2014,the average of average annual cropland NPP in Fujian province was 677.21gC·m-2·a-1,and the range of variation was 552.58-770.19,gC·m-2·a-1;The average NPP of the year was 10.02 TgC·a-1,with a range of 8.19-11.42 TgC·a-1(1 Tg=1012g).During the whole study period,the annual variation of cropland NPP showed an upward trend,while the trend of annual linear change was not significant(P>0.05).From the point of spatial distribution,the average of average annual cropland NPP of each district cities of Fujian province in 2000-2014 changes ranging of 576.98gC·m-2·a-1-769.02gC·m-2·a-1.Descending order is:Quanzhou>Zhangzhou>Longyan>Ningde>Putian>Xiamen>Sanming>Fuzhou>Nanping,mainly related to the geographical conditions,the cultivated land around the city level of soil fertility and crop cropping system.totalcropland NPP of one year over the same period range 115.33-1577.33 GgC·a-1(1 Gg = 109 g),with descending order:nanping>Zhangzhou>Longyan>Ningde>Sanming>Fuzhou Quanzhou>Putian>Xiamen,mainly related to the degree of farmland area and land use.(2)Cropland NPP in Fujian province mainly presents the trend of high eastern and western low.According to the spatial distribution of farmland productivity levels estimated by cropland NPP,during the years of 2000 to 2014,Fujian province had the largest area of low-yield farmland,followed by middle class farmland and the smallest area of high-yield farmland.High-yielding farmland and middle farmland are mainly distributed in the eastern coastal cities,and low-yield farmland is mainly distributed in the western mountainous areas.(3)Cropland NPP from 2000 to 2014 by pixel trend analysis shows that 66.12%of the area of the cropland NPP showed a trend of increase,and 33.88%showed a trend of decrease.The increase of area are mainly distributed in the coastal.Significance test shows that 89.72%of cropland NPP showedthe trend of reduced and increase not significantly(p>0.05).No significant increase of the area are mainly distributed in coastal areas,while not significantly reduce of the area are mainly distributed in mountainous cities.(4)Cropland NPP and climate factors related to the simple correlation analysis shows that under the condition of combination of three kinds of climate factor,solar radiation had the largest positive effect on cropland NPP in Fujian province;The less effect is precipitation,which is negative to the cropland NPP.More precipitation may inhibit the growth of farmland vegetation.The least effect is the temperature,temperature had positive effect onhalf of regional NPP,while no biginfluenceon 25%of the area,and the temperature is too high to the vegetation carbon sequestration in few areas.Cropland NPP and climate factors related to the partial correlation analysis Shows:without considering the three climate factors,the solar radiation had largest effect on NPP,followed by precipitation,the last is the temperature.The regional difference between the influence of precipitation and temperature on NPP is more apparent.