Monitoring Nitrogen Status In Wheat And Rice With Leaf Chlorophyll Fluorescence Parameters

Active chlorophyll fluorescence technology could be used to monitor leaf nitrogenstatus of crop plants in modern precision agriculture. Based on the field experimentsinvolving different wheat and rice cultivars under varied nitrogen levels, the characteristicsof leaf fluorescence parameters in rice and wheat under different treatment conditions andtheir relationships to leaf nitrogen status were determined in this study. Then, thefluorescence parameter based-models were developed for monitoring leaf pigment contentsin wheat. The sensitive reflectance spectral parameters for indicatingleaf fluorescenceparameters were also established. The overall results help. to provide a new technicalapproach for monitoring of physiological status in crop plants.From the field experiments, the change patterns of leaf nitrogen contents andfluorescence parameters over growth progress in different wheat cultivars were determinedunder different nitrogen levels, the correlative relationships of leaf nitrogen contents tofluorescence parameters were established, and the regression equations for predicting leafnitrogen contents were formulated. The results showed that the leaf nitrogen contents andfluorescence parameters at different leaf positions of wheat increased with raised nitrogenlevels. From booting to maturity, fluorescence parameters F_v/F_m and F_v/F_o of wheatleaves initially increased and then decreased with growth progress. Leaf nitrogen contentsof different leaf positions in wheat had significant positive correlations with fluorescenceparameters F_m, F_v, F_v/F_m, F_v/F_o, F_s and F_o', especially the correlation in the 1st and 2nd leaffrom top was best. Leaf nitrogen contents of different wheat cultivars were significantlyrelated to fluorescence parameters F_v/F_m and F_v/F_o, with average R² of 0.66 and 0.61,respectively. For different cultivar types with low, medium and high grain proteincontents, an integrated regression equation could be used to describe the dynamic changepattern of leaf nitrogen contents at top two leaves with fluorescence parameter (F_v/F_o).The change patterns of leaf nitrogen accumulation and fluorescence parameters overgrowth progress in different wheat cultivars were determined under different nitrogen levels, the correlations of leaf nitrogen accumulation to fluorescence parameters were analyzed,and the regression equations for predicting leaf nitrogen accumulation were established.The results showed that the leaf nitrogen accumulations and fluorescence parameters atdifferent leaf positions of wheat increased with increasing nitrogen levels. Leaf nitrogenaccumulations of different leaf positions in wheat had significant positive correlations withfluorescence parameters F_m, F_v, F_v/F_m, F_v/F_o, F_s, F_v'/F_m' and F_o', especially the correlationin the 1st and 2nd leaf from top was best. Leaf nitrogen accumulations of different wheatcultivars were all significantly related to fluorescence parameters F_v/F_o, with average R² of0.74. For different cultivars with low, medium and high grain protein contents, differentregression equations were suggested to describe the dynamic change pattern of leafnitrogen accumulations at top two leaves with fluorescence parameter (F_v/F_o), which couldenhance the accuracy of prediction. The results indicated that fluorescence parametersFv/Fo could be potentially used to estimate the leaf nitrogen accumulation in wheat.The fluorescence parameters of the top 4 leaves on stems of two rice cultivars weremeasured with FMS-2 at different growth stages under three nitrogen levels, and the leafnitrogen contents and accumulation were correspondingly determined by destructivesampling and chemical assay. The results showed that the leaf nitrogen contents, nitrogenaccumulation and fluorescence parameters changed significantly with nitrogen levels,tending to increase with the nitrogen application rates. The fluorescence parametersexhibited a parabolic shape over the growth progress, initially increased until heading andthen decreased to the lowest from heading to maturity. The distributions of fluorescenceparameters on main stem in all treatments were L1＞L2＞L3＞L4. With a single cultivar, leafnitrogen contents of single leaf positions were significantly correlated to fluorescenceparameters, with better performance in Huajing 2 than in Wuxiangjing 9. With combinedrice cultivars, leaf nitrogen contents of different leaf positions were linearly related tofluorescence parametersΦ_PSâ…¡ and qP. Different regression equations should used toestimate leaf nitrogen contents at different leaf positions withΦ_PSâ…¡ and qP. Fluorescenceparameters F_m and F_v were significantly correlated to leaf nitrogen accumulation. Theresults indicated that fluorescence parameters (Φ_PSâ…¡, qP) and (F_m, F_v) could be potentiallyused to indicate the leaf nitrogen contents and accumulation in rice, respectively.The leaf pigment concentrations and fluorescence parameters at different leaf positionsin different wheat and rice cultivars were investigated under different nitrgen rates, the quantitative relationships of leaf pigment concentrations to fluorescence parameters wereestablished. The results showed that the leaf pigment concentrations and fluorescenceparameters at different leaf positions of wheat and rice varied distinctly with nitrogen rates,Chl a, Chl (a+b), Car, and fluorescence parameters F_v/F_m and F_v/F_o all increased withincreasing nitrogen rates, while Chl a/b values decreased. From jointing to maturity, thefluorescence parameters F_v/F_m and F_v/F_o of wheat leaves decreased with growth progress.The distributions of fluorescence parameters on main stem in all treatments were L2＞L1＞L3＞L4. With a single cultivar, the leaf pigment (Chl a, Chl (a+b),Car) concentrationsand Chl a/b values at different leaf positions were positively correlated with fluorescenceparameters F_m, F_v, F_s, F_m', F_o', F_v/F_m, F_v/F_o and F_v'/F_m'. With combined wheat cultivars,fluorescence parameters F_s, F_m and F_v/F_o could accurately estimate leaf Chl a, Carconcentrations and Chl a/b values at different leaf positions, respectively. The pigmentconcentrations of rice were much lower correlated to fluorescence parameters than wheat,andΦ_PSâ…¡ could be used for estimating leaf Chl a concentrations of rice. Thus it is feasibleto estimate the leaf pigment concentrations and Chl a/b values in wheat and rice withfluorescence parametersLeaf net photosynthetic rate and transpiration rate in wheat and rice under differentnitrogen levels and its relationships to fluorescence parameters were studied. The resultsshowed that leaf net photosynthetic rate and transpiration rate increased with increasednitrogen levels in wheat and rice. The fluorescence parameter F_v was positively andlinearly related to leaf net photosynthetic rate in wheat and negatively and linearly relatedto leaf transpiration rate in rice. It is concluded that the fluorescence parameter F_v could beused to monitor leaf net photosynthetic rate in wheat and leaf transpiration rate in rice.Different regression equations should be used to estimate leaf net photosynthetic rate inwheat and leaf transpiration rate in rice at different leaf positions.The relationship between leaf fluorescence parameters and leaf spectral reflectance inwheat under different nitrogen levels were further established. The leaf fluorescenceparameters (F_v/F_m, F_v/F_o) in wheat increased with increasing nitrogen application. Theleaf spectral reflectance varied distinctly with nitrogen rates, leaf positions and growthprogress. For different leaf positions, the correlations of leaf spectral reflectance of 1stand 2nd leaves to fluorescence parameters were stabilized in visible light (550-680nm) andnear infrared (750-850nm). The leaf reflectance spectral indexes DVI(750,550), DVI(735,690) and TVI could be used to quantitatively monitor leaf fluorescenceparameters F_o, F_m, F_v, F_v/F_m, F_v/F_o, F_s, F_m', F_o', F_v' and F_v'/F_m' of top 2 leaves. The abovedynamic relationships of leaf fluorescence parameters to leaf reflectance spectra wereapplicable for different cultivars, growing stages and nitrogen levels in wheat. Thus, theleaf fluorescence parameters could be predicted with leaf reflectance spectra.