Response Of The Leaf Maximum Carboxylation Rate To Nitrogen And Hyperspectral Inversion On Cotton

The maximum carboxylation rate(Vcmax)of plant leaves is one of the most important parameters to characterize the photosynthetic capacity of vegetation.Accurate simulation of Vcmax is of great significance to predict the photosynthesis and future productivity of vegetation.The experiment was set up in 2018 and 2019 on the Sanfenchang Experimental Plot of Hebei Agricultural University.Transgenic insect resistant Guoxinmian 9 cotton was used as the experimental material.Four nitrogen application levels were set up:0(N0),120(N1),240(N2),480(N3)kg·hm-2 in a randomized block design,repeated three times.The effects of different nitrogen application levels on Vcmax of cotton leaves were studied.The physiological parameters and reflectance spectra of cotton leaves at different growth stages were measured.The main results followed that:1.The Vcmax of cotton showed a seasonal change trend from high to low with the growth period,which reached the maximum value at the seedling stage.Under the premise of high basic soil fertility,leaf Vcmax is not affected by the level of nitrogen application from seedling stage to bud stage.As the growth period progresses,nitrogen has gradually become one of the main factors affecting its height.In addition,high nitrogen fertilization can keep the leaf Vcmax at a high level later in the growth period.2.The change of nitrogen application level can significantly affect the physiological parameters of cotton leaves.With the increase of nitrogen application,the content of soil nitrogen increased,the content of nitrogen in cotton leaves,the proportion of nitrogen in the carboxylation system(PR),chlorophyll content,SPAD,leaf mass per area,the actual photochemical quantum yield(φPSⅡ)and Rubisco carboxylase activity all increased,and reached a significant difference in some growth periods(after the catchy period in 2018 and the boll period in 2019),only The maximum photochemical quantum yield(Fv/Fm)was less affected by nitrogen application.Among them,the nitrogen content of leaves was consistent with PR,and the chlorophyll content was consistent with SPAD.In addition,the level of nitrogen application had no significant effect on the growth and development of cotton seedlings.3.There is a good correlation between Vcmax of cotton leaves and some physiological parameters,which has the potential to retrieve Vcmax of cotton leaves.Among them,the correlation between Vcmax and nitrogen content,PR(R2=0.705),chlorophyll content,cpPSII(R2=0.528)in carboxylation system was higher than that of other physiological parameters.A univariate linear regression model and multiple stepwise regression model with physiological parameters as independent variables and Vcmax of cotton leaves as dependent variables was constructed.Among them,the model based on nitrogen content and chlorophyll of leaves was the best(R2=0.801,RMSE=17.01 μmolm-2s-1),the model based on leaf nitrogen content was the second(R2=0.717,RMSE=20.54 μmolm-2s-1),and the model based on other physiological parameters had the lowest accuracy.So was the validation result.4.The leaf Vcmax of cotton is significantly correlated with the blue and red edge bands of the spectral reflectance,and from this the spectral index that can better predict the cotton leaf Vcmax:normalized spectral index(NDVI697,445)and specific spectral index(SR445,694).In the construction of the blade Vcmax estimation model with the spectral index as the independent variable,the accuracy of the blade Vcmax estimation model constructed by NDVI697,445 and SR445,694 is much higher than other univariate estimation models,and R2 exceeds 0.75.In addition,the multiple stepwise regression model constructed by SR445,694,PRI,and mND705 has the highest accuracy(R2=0.809,RMSE=16.93μmolm-2s-1);the verification result is also the same.In conclusion,Vcmax is more sensitive to leaf nitrogen in cotton leaves,and the relationship between Vcmax and nitrogen content in cotton leaves is better than other physiological parameters,but the relationship with Rubisco carboxylase activity is weak.It is affected by nitrogen content in cotton leaves and PR in cotton leave.In addition,the accuracy and accuracy of the model based on leaf spectrum are higher than those based on physiological parameters,which shows that it is feasible to retrieve the Vcmax of cotton leaf by leaf spectrum,and the research results can provide theoretical and model support for the spectral inversion of vegetation leaf Vcmax.