Spatial-temporal Patterns And Driving Factors Of Vegetal NPP In The DongTing Lake Basin

Net primary production(NPP)of vegetation represents the production capacity of natural ecosystems.It is also an important index to evaluate ecosystem carbon sink and to clarify ecosystem response to global changes.The paper takes the Dongting Lake Basin as study area,which is the vital ecosystem in the middle reaches of the Yangtze River,this paper reveals the temporal and spatial variation characteristics and driving factors of vegetal NPP from 2000 to 2019 by using multi-source data such as remote sensing photos,ground monitoring data,statistical yearbook and many others.Then,Biome-BGCMuso model is used to simulate,predict and analyze the NPP value and its response pattern to global changes of forest,grass and cropland from 2050 to 2100.The main contents and conclusions are as follows:(1)It shows that plants in the study area is at the level of medium and high productivity during the study period with the multi-year average NPP value of 0.65Kg C/m~2/a.The high value area is located in the west,south and southeast of the basin,whereas the low value area nears the lake and in the middle of the basin.In the past two decades,the vegetal NPP in Dongting Lake Basin showed a stable but slight growing trend,and the spatial layout was relatively balanced without obvious migration,the reduced areas were mainly concentrated in the north,southeast and south,accounting for only 21.78%of the overall area.According to the types of land use,the NPP growth rate of grassland was the fastest(3.9g C/m~2/a),cropland came later(2.8g C/m~2/a),forest was the slowest(2.0g C/m~2/a).(2)The results of Geo Detector factor detection show that the leading driving factors on vegetation NPP in Dongting Lake Basin are land use,precipitation,DEM and air temperature.Land use has a decisive impact on vegetal NPP.DEM and air temperature have an obvious positive correlation with vegetal NPP,and there is no correlation between precipitation and vegetal NPP.Besides,bi-factor detection reveals significant results that combinations of precipitation-land use,temperature-land use,temperature-precipitation and DEM-temperature show significant nonlinear enhancement effect,while land use-DEM and precipitation-DEM show alternating effect within nonlinear and linear enhancement effect.(3)Future scenario simulation shows that under L scenario,the vegetal NPP has decreased in every land use,the decline range of forest has reached 9.5%,but the decline range of grassland and cropland is small.The vegetal NPP of different land use types under M and H scenarios has similar change laws,the forest shows the decline trend of slowing down,while the grass and cropland have the growth trend of slowing down.Spatially,simulation of NPP changes can see that the Dongting Lake Basin has an increase under the transformation from L to H scenario as a whole.The Western projecting part,the northwest broken zone,the southern and southeastern edge areas are the high-value areas of NPP,while the low-value areas near the lake.In addition,the distribution of predicted vegetal NPP changes is closely related to land use types,the change of forest is the smallest(negatively),and the change of grass is the largest(positively).(4)Finally,the response of vegetal NPP to the changes of environmental factors(concentration of C and N,temperature and precipitation,short as C、N、T、P)is analyzed and predicted based on Biome-BGCMuso model.Among the single factors,vegetation is sensitive to the change of temperature mostly,and the double factor C×T、N×T、T×P combinations have the greatest impacts on vegetal NPP,the temperature and the three double factor combinations have a negative impact on forest of 30-50 g C/m~2/a,a positive impact on grass of 0-20g C/m~2/a,and there is no obvious law in cropland.Three factor C×N×T、C×T×P、N×T×P and four factor combinations have the above similar law for forest and grass,but at this time,the cropland as a whole shows the trend that the simulated NPP change range decreases with the increase of step length and change from L to H scenario.The paper analyses the temporal and spatial patterns of vegetal NPP in the Dongting Lake Basin from 2000 to 2019,quantitatively extracts the driving factors of vegetal NPP in the study area,and predicts the change of vegetal NPP in the future.The results are helpful to comprehend the change law and internal influencing mechanism of the productivity renewal capacity of the ecosystem in the Dongting Lake Basin which can provide scientific auxiliary basis for watershed ecosystem management and governance.