Estimation Model Of Maximum Carboxylation Rate Of Winter Wheat And Summer Maize In North China Plain Based On Leaf Nitrogen Content And Photosynthetic Pigments

As an important part of terrestrial ecosystem,farmland ecosystem plays a very important role in terrestrial carbon cycle.Accurate simulation of the dynamic change of maximum carboxylation rate(V_cmax25)based on leaf nitrogen content(N_area)and photosynthetic pigments(chlorophyll content Chl_area and carotenoid content Car_area)is very important to predict vegetation productivity.However,there is still great uncertainty about the dynamic research of V_cmax25 in farmland ecosystem.In this study,the farmland ecosystem of Yucheng Station in China was taken as the research object,and the dynamic changes of photosynthetic parameters(V_cmax25 and maximum electron transfer rate J_cmax25),N_area,Chl_area and Car_area of winter wheat and summer corn leaves at different growth stages were measured.The limiting effect of leaf nitrogen content and photosynthetic pigments on V_cmax25 was analyzed,and the V_cmax25 estimation model was built to improve the simulation accuracy of the model,which provided technical support for carbon budget assessment of farmland ecosystem in North China Plain.The research results are as follows:（1）During the observation period,the seasonal variation trends of photosynthetic parameters(V_cmax25 and J_cmax25)and photosynthetic pigments of winter wheat and summer corn leaves are consistent,and they all start to rise slowly at jointing stage,reach the peak at flowering stage,and then gradually decrease.However,the seasonal variation trend of N_area in winter wheat and summer corn leaves is different from that of photosynthetic pigment and V_cmax25,and its peak value appears at jointing stage and flowering stage.This may be due to the dynamic distribution of nitrogen to different nitrogen pools,resulting in different trends of nitrogen content in leaves from other parameters.（2）N_area,Chl_area and Car_area of winter wheat leaves have strong correlation with V_cmax25（R²=0.54,P<0.001,R²=0.75,P<0.001,R²=0.57,P<0.001）,among which Chl_areaof winter wheat leaves has the highest correlation with V_cmax25;There is also a high correlation between N_area and Chl_area of summer maize leaves and V_cmax25（R²=0.63,P<0.001,R²=0.71,P<0.001）,but a low correlation between Car_area and V_cmax25（R²=0.38,P<0.001）.（3）Path analysis of the leaf parameters of winter wheat and summer corn showed that the Chl_area of the leaves of the two crops contributed the most to the seasonal variation of V_cmax25.Winter wheat leaves affected V_cmax25 through the direct action of Chl_area and Car_area,while summer corn affected V_cmax25 through the direct action of Chl_area and Car_area through the indirect action of Chl_area.（4）Through multiple regression analysis of winter wheat-summer corn leaves N_area,Chl_area and Car_area with V_cmax25,it was found that among the four photosynthetic models(N_area-Chl_area,Chl_area-Car_area,N_area-Car_area and N_area-Chl_area-Car_area),The N_area-Chl_area-Car_area model has the highest estimation accuracy（R²=0.81,P<0.001,R²=0.87,P<0.001）,which indicates that leaf N_area may have some limitations in estimating V_cmax25,and the addition of photosynthetic pigments(Chl_area and Car_area)can significantly improve the estimation accuracy of winter wheat and summer corn V_cmax25.