Predictability Of Global Sunlight-induced Chlorophyll Fluorescence On Total Primary Vegetation Productivity And Its Response To Drought

Sun-induced chlorophyll fluorescence(SIF)is a spectral signal emitted by the photosynthetic center of plants under solar illumination,with a wavelength of 650?860 nm.As a by-product of photosynthesis,it is closely related to plant photosynthesis and contains rich photosynthetic information,which provides new technologies and ideas for land vegetation observation.In recent years,with the development of remote sensing technology,a variety of satellite based remote sensing SIF products have been generated.Gross primary production(GPP)is the total amount of carbon absorbed by green plants through photosynthesis,which reflects the production level of terrestrial biosphere in the natural environment.Accurate quantification of global and regional terrestrial GPP is of great significance to the study of global carbon cycle and ecosystem function assessment.Compared with vegetation index,chlorophyll fluorescence is more sensitive to vegetation photosynthesis.Using SIF to estimate GPP has gradually become a new model to estimate GPP.A comprehensive understanding and quantification of the relationship between SIF and GPP is the premise and foundation of effectively using SIF to estimate and monitor GPP of terrestrial ecosystems.However,the relationship between SIF and GPP is still controversial due to the influence of many factors.On the basis of evaluating multi-source remote sensing SIF products based on ground observation data,this study uses remote sensing SIF data and GPP data to study GPP-SIF relationships at different scales,the influence of meteorological factors on the spatio-temporal variation of GPP/SIF is analyzed,and the response of GPP and SIF to drought events in Southeast Asia is monitored to provide reference for understanding the relationship between GPP and SIF.The main research contents and conclusions of this paper are as follows:(1)This study obtains multi-source remote sensing SIF products.Firstly,the consistency of different products on a global scale is compared.The six products have similar spatial distribution characteristics on the annual scale,and the annual average value and maximum value are quite different.On the monthly scale,the change trend of data sets based on OCO-2and GOME-2 is different,except SIF_LUEPKthere is a good correlation between other remote sensing SIF data sets.From 2007 to 2016,GOSIF and CSIF were mainly rising above the global land,but SIF_LUEJJ,SIF_LUEPKand SIF₀₀₅showed a downward trend.There are great differences between different remote sensing SIF products and ground SIF observation data.Generally speaking,the satellite-based SIF data set has good correlation with coniferous forest station observation data,but poor correlation with farmland ground observation data.(2)The spatial variation characteristics of GPP and SIF were examined by GPP/SIF.GPP/SIF can be expressed as the ratio of LUE and SIF_yield,and can represent the dynamic change of light energy utilization relationship between GPP and SIF.Different from the spatial patterns of GPP and SIF,GPP/SIF has obvious spatial heterogeneity.In the growing season,the high value areas of GPP/SIF are mainly distributed in 60°north latitude and tropical rain forest areas,while the low value areas are concentrated in arid areas such as central North America,Southern Africa and Australia.GPP/SIF changes with different vegetation types and climate types,and shows an obvious seasonal change trend on a monthly scale.At the same time,the GPP-SIF relationship is affected by environmental factors and is highly sensitive to precipitation.The correlation between GPP/SIF and temperature and precipitation in growing season changes with climate types.(3)Under drought stress,the change trend of SIF and GPP will be different.Combined with the data of drought index,solar radiation,temperature and precipitation,the response of SIF and GPP to drought in Southeast Asia in 2015/16 was studied.It is found that GPP/SIF is greater than the multi-year average in the early stage of drought and less than the multi-year average in the late stage of drought.On the spatial scale,the decline of GPP is greater than that of SIF.Compared with SIF,SIF_yieldand GPP have higher correlation and can better indicate the change of GPP during drought.During the drought period,the correlation between GPP/SIF and temperature increases.APAR is the environmental factor that has the greatest impact on the change of GPP,and precipitation is the environmental factor that has the greatest impact on the change of SIF.