Effects Of Different Ratio Of Nitrogen Status On Photosynthetic Physiology And Endogenous Hormones Of Citrus Cultivar Huangguogan

Auxin（IAA）,abscisic acid（ABA）,Gibberellic acid（GA）and zeatin nucleosides（ZR）are not only closely related to plant growth and development,but also play a very important role in the process of nitrogen uptake and metabolism.Therefore,according to the optimum nitrogen application rate in different fertilizer periods,the nitrogen content was converted into different ratios of nitrate nitrogen（NO₃^-）and ammonium nitrogen（NH₄⁺）,which were100,75,50,25,75 and 100,respectively,and the corresponding treatments were 1:5.The control（CK）was conventional urea fertilizer treatment.The contents of four kinds of endogenous hormones in root,leaf,pericarp and pulp were determined at the young fruit stage,the expansion stage,the color conversion stage and the mature stage,respectively,and the effects of different nitrogen status on the changes of endogenous hormones in different parts of Citrus huangguo were studied.The fruit quality and photosynthetic physiology of Citrus mandarin were measured at maturity stage,and the correlation and grey correlation analysis were carried out to reveal the response of Citrus cultivar Huangguogan to the photosynthetic characteristics and fruit quality of different nitrogen forms.The optimum ratio of different nitrogen forms of Citrus mandarin under the optimum nitrogen fertilizer rate was further determined.The experiment concluded as follows:The main results were as follows:（1）When the ratio of nitrate nitrogen to ammonium nitrogen was 75:25,the contents of total sugar,soluble solids,vitamin C and sugar-acid ratio were the highest.Comprehensive grey correlation analysis showed that nitrate nitrogen:ammonium nitrogen=75:25 was beneficial to the improvement of fruit quality.（2）With the increase of ammonium nitrogen ratio,the openness of PSⅡand the photochemical electron transfer efficiency of PSⅡwere decreased,and the conversion of light energy decreased,which resulted in the decrease of the amount of light energy used in photosynthesis.Thus,the net photosynthetic rate is reduced.Therefore,the increase of nitrate ratio is more beneficial to the photosynthetic performance of Huangguogan plants.When the ratio of nitrate nitrogen to ammonium nitrogen is 75:25,the net photosynthetic rate of Huangguogan is the highest,thus accumulating more photosynthetic products for the formation of fruit quality.（3）The grey correlation degree analysis showed that when the ratio of nitrate nitrogen to ammonium nitrogen was 75:25,the correlation degree between plant and ideal endogenous hormone level was the largest,so with the increase of nitrate/nitrogen ratio,the level of plant growth hormone IAA,ZR,GA₃ was increased.The level of ABA is reduced.Through correlation analysis,the increase of IAA content and IAA/ABA ratio was significantly correlated with the improvement of fruit quality,so the ratio of nitrogen forms was mainly to increase the size of fruit cells to increase the appearance quality of fruit.There was a significant correlation between the improvement of internal quality and the increase of plant IAA level.