The Study Of The Gross Primary Productivity And Spatial Patterns In The Qinghai Lake Basin From2010 To 2020

In the context of climate warming,research on the carbon cycle of terrestrial ecosystem has gradually become a hot topic.As an indispensible part of the global ecosystem,terrestrial ecosystem plays an decisive role in mitigating greenhouse effect and regulating climate change in the global ecological environment.Gross Primary Productivity（GPP）refers to the total amount of organic carbon fixed in the leaves and stems of green plants during photosynthesis.The initial energy of terrestrial ecosystem is determined by the GPP,therefore,accurate estimation of GPP through model simulation and measured data is of great significance for the global terrestrial ecosystem carbon cycle.The Tibetan Plateau is the highest and largest plateau in China.Its ecological statues is very important in China and even the whole East Asia,which is known as the"roof of the world"and an important initiation area for global climate change.Qinghai Lake Basin is located at the northeastern edge of Tibetan Plateau,at the intersection of monsoon and arid areas,with a fragile ecosystem that are sensitive to climate change.Qinghai Lake Basin has large rugged terrain,rich vegetation species,obvious horizontal and vertical differentiation,and a natural security barrier against the spread of western desert.vegetation photosynthesis model（VPM）is an improved model of light energy use efficiency.In this study it has to simulate the GPP in the Qinghai Lake watershed using MODIS-GPP data products,meteorological data and other relevant data.Combining with MODIS-GPP data,the accuracy of the simulation results was evaluated and verified,the temporal and spatial distribution characteristics of the GPP in Qinghai Lake Basin were analyzed,and the influencing factors affecting the dynamic changes of the GPP in Qinghai Lake Basin were discussed.The contribution rate of each influencing factor was quantified by using the geographic probe model.The research results are as follows:（1）Accuracy verification and reliability evaluation of the simulation results of the VPM model are carried out with MODIS-GPP data.The results show that,on the interannual scale,the linear fitting coefficient R²between GPP_VPMand GPP_MODISis0.58,RMSE=55.05,RE=-65.62%.Therefore,GPP_VPMand GPP_MODIShave a good consistency on the interannual dynamic changes,and the simulation results of VPM model are reliable,and the model simulation results can be used for other analysis and calculation in the later period.（2）The photosynthetic active radiation（PAR）in the Qinghai Lake Basin fluctuated between 49.70-374.22MJ?m^-2·month^-1from 2010 to 2020,and the maximum value of PAR occurred in May 2014(374.22MJ?m^-2·month^-1).The minimum value of 49.70 MJ?m^-2?month^-1occurred in June 2016,and the multi-year mean photosynthetically active radiation（PAR）values ranged from 292.54 to 304.79MJ?m^-2?a^-1.The monthly land surface moisture index（LSWI）in the growing season from 2010 to 2020 fluctuated between-0.13 and 0.42,with an average value of 0.037.The maximum value was 0.42 in July 2013,and the minimum value was-0.13 in May2014.The multi-year average surface water index fluctuates between-1.36 and 1.62.On the time scale,the photosynthetic active radiation（PAR）and land surface moisture index（LSWI）showed a fluctuating trend.On the spatial scale,both PAR and land surface moisture index（LSWI）showed"low-high-low"distribution characteristics.（3）In terms of time scale,the change trend of GPP in the study area is as follows:GPP increases from May to July（or August）,and decreases from August to September.In each growing season,GPP reaches its peak in July.The monthly mean value of GPP fluctuated in the range of 1.17～169.4 g C·m^-2,with the highest monthly mean value in July 2012(169.4 g C·m^-2)and the lowest monthly mean value in September2020(1.17 g C·m^-2).On an annual scale,the average annual GPP in the last 10 years of the growing season varied in the range of 19.67～83.6 g C·m^-2,with the lowest average in 2017(19.67 g C·m^-2)and the highest in 2013(83.6 g C·m^-2).On a spatial scale.The spatial distribution characteristics of GPP in Qinghai Lake Basin are"low-high-low",that is,the GPP gradually increases from the northwest and eastern regions to the middle of the basin（4）It was analyzed by a geographic detector,the change of the GPP in Qinghai Lake Basin is not determined by a single factor,but is driven by air temperature and NDVI.The q value after the interaction of the two factors is greater than that of the single factor,and the interaction is shown as the double factor enhanced type and the independent type.In the single factor detection,the change of GPP was mainly affected by temperature,elevation and vegetation normalization index,indicating that meteorological factors were closely related to the change of GPP.In the two-factor driven model,NDVI（vegetation cover）and other factors showed high explanatory power,while the interaction detection results of land use type with average annual precipitation and average annual temperature were not very ideal,indicating that vegetation factors and natural factors jointly drove the change of GPP.