Effect Of Nitrogen On Correlation Between Chlorophyll Fluorescence And Photosynthesis Of Crops Basing On Combined Observation Of Active And Passive Remote Sensing

Sun induced chlorophyll fluorescence（SIF）monitoring is a new technology for quantitative remote sensing monitoring.Gross primary productivity（GPP）is a measure of how much carbon is absorbed through photosynthesis by terrestrial plants,which plays an important role in driving the function of global ecosystem.The precise measurement of GPP in terrestrial ecosystems is crucial for a comprehensive understanding of the carbon cycle in terrestrial ecosystems.In view of the close physiological relationship between chlorophyll fluorescence and photosynthesis,satellite-based SIF has become a powerful method to estimate GPP in terrestrial ecosystems.However,the relationship between GPP and SIF is affected by various factors,such as environmental conditions,canopy structure,vegetation functional type,and vegetation physiological state.Multiple fluorescence quantitative remote sensing monitoring instruments were combined and modified to realize the active and passive combined simultaneous observation of chlorophyll fluorescence,in order to explore the complex correlation mechanism between chlorophyll fluorescence and photosynthesis.Secondly,the improved instrument was used to observe the chlorophyll fluorescence of rice（C₃）and maize（C₄）leaves in different nitrogen levels at daily and seasonal scales,coupled with the gas exchange measurements.Finally,the rice in different nitrogen concentrations in the field experiment was taken as the research object.Active fluorescence measurement was performed on leaves,passive observation was performed on canopy,both coupled with the gas exchange measurements.The main conclusions were as follows:（1）The chlorophyll fluorescence active and passive combined synchronous observation system could obtain rich fluorescence parameters of crops,such asФ_P,Ф_F,Ф_NPQ,SIF_yield,and NPQ,through combining Fluo Wat leaf clip,QEpro spectrometer and PAM fluorometer.It is helpful to analyze the relationship between fluorescence and photosynthesis at leaf scale.（2）The relationships between net photosynthetic rate A_n and SIF were nonlinear and nitrogen dependent.The relationships were also different between rice and maize.Ф_D andФ_NPQ had effects on the relationship between fluorescence and photosynthesis（Ф_P/Ф_F）,and the effects were different between rice and maize.Nitrogen addition alleviated photoinhibition effectively in the leaves of rice and maize（Ф_D>0.2）,and also reduced the effect of high heat dissipation onФ_P/Ф_F in the leaves of maize(Ф_NPQ>0.38).（3）SIF/GPP decreased with the increase of leaf nitrogen content N.Nitrogen could also affect the relationship between SIF and GPP through physiological factors.The regulatory mechanisms of different nitrogen concentrations were significantly different.With the increase of N,the optimal regulation of the relationship between SIF and GPP shifted from C_ab,to APAR,and then to G_sw gradually.Specifically,C_ab,APAR and G_sw were the main factors in low,medium and high nitrogen treatment.