The Effects Of Nitrogen On Photosynthetic Energy Transformation And Water Use Efficiency Of Wheat Leaves

To increase crop water use efficiency and drought-resistance is one of the importantcontents of water-saving agriculture, fertilizing in order to save water, especially,supplying nitrogenous fertilizer to regulate crop water use efficiency and amend thedrought-resistant ability are the hotspot both in theory and practice field. The two wheatcultivars with similar ecological characteristics and different drought-resistance had beenselected as experimental materials, and the different nitrogen levels also used astreatments in this study. Photosynthetic gas exchange parameters, chlorophyll fluorescenceparameters, ABA and NO content, the activity of protectase, aboveground biomas, plantwater content and yield were determined. The relationship among leaf NO content,ABAcontent and WUE, the regulating mechamism of nitrogen on the trans-conductanceand distribution of excitation energy, the relationship among leaf total N content, leaf ABAcontent and WUE, and the effects of nitrogen on leaf cell membrane stability had beenstudied to search the physiological methods which can increase drought-resistance andameliorate water use status of wheat. The main results described as below.(1)The effects of nitrogenous fertilization on the relationship among leaf NO content,ABA content and water use efficiency and its mechanism regulated the drought-resistantability was clafiried basically. The leaf NR activity had positively linear correlation withNO content in tillering and jointing stage (R2≥0.68,n=15), leaf NR activity was enhancedwith the increasing of nitrogen fertilization content and further to increase NO content andthen adjust stomatal opening. The leaf ABA content was positively related with leaf NOcontent at N360 treatment, but negatively related in the lower nitrogen levels. Thedrought-resistance depend on the stomatal sensitivity to leaf NO content on the stomalevel, the stoma of dryland cultivar could rapidly response to the changing of leaf NOcontent. The reasonable nitrogen application (N180 treatment) could maintain lower leafNO content and sustain the stoma opening, to promote the gas exchange and increase IWUE of sensitive cultivar, increase the stomatal sensitivity to leaf NO content of drylandcultivar, enhance the responsible sensitivity of dryland cultivar to drought condition.(2)The regulated mechanism of nitrogen on the trans-conductance and distributionof excitation energy were revealed. Nitrogen improved the photosynthetic pigmentcontent in leaves of different drought resistance cultivars, decreased respiration rate.Although nitrogen could not significantly change the distribution ratio of excitationenergy between PCR and PCO, but it improved the electron flow at the PCR direction.Excessive nitrogen fertilization could enhance the dark respiration of leaf.ΦPSⅡdecreased first and then increased as the increasing of leaf total N. There was linearpositive correlation between Pn andΦPSⅡ. These proved that nitrogen could amelioratethe competition relationship of excited energy between heat dissipation andphotochemistry reaction and increase the ability of photosynthetic instruments so thatmore light energy could enter the process of carbon assimilation, and increase IWUEfinally.(3)The relationship between leaf total N content and ABA content and its effects onWUE was primarily clarified. Leaf total N and ABA content of the two cultivars weresignificant negative linear correlation when nitrogen supplied, reasonable nitrogenfertilization could strengthen the reciprocal effects between ABA content and total Ncontent in flag leaves, whereas, excessive N did decrease this interaction. The sensitivityof leaf IWUE to ABA content was increased with the increasing of nitrogen fertilization;GWUE had negatively linear correlativity with ABA content in flag leaves. The total Ncontent and GWUE had significant negatively quadric correlation with each other in flagleaves, which showed that appropriate application of nitrogen content can maintain thereasonable level of leaf total N content, increase photosynthetic rate to accelerateaccumulation of dry matter and enhance instantaneous WUE to bring about the incrementof wheat yield and water use efficiency.(4)The effects of nitrogen application on celluar membrane anti-peroxidation of wheat leaves was explicited. The application of nitrogen increased leaf CAT and SODactivity, decreased XOD activity,H2O2 and MDA content. N0 treatment in dryland cultivarhad higher activity of protectase and lower XOD activity,H2O2 and MDA content thansensitive cultivar. Cellular membrane stability have close correlation with wheat resistanceto drought, thereby nitrogen application enhanced the adaptability to drought byincreasing leaf anti-peroxidation of wheat.(5)The effects of nitrogen application on yield and configuration developing ofwheat was validated. Nitrogenous fertilizer could increase leaf photosynthetic pigment inorder to increase Pn, and it also could maintain the stoma opening and improve gasexchange, and the dry matter assimilation was enhanced. The plant height and spike lengthwas increased after nitrogen supplied, although kilo-grain weight was decreased but thespike grain weight was increased compared the N0 treatments. The group growth wasimproved by nitrogen fertilizer, the leaf area index was increased significantly afternitrogen supplied, and the yield, water use efficiency and harvest index were enhancedfinally.