Comparison Of Structural Characteristics Related To Water Metabolism Between Different Citrus Types And Study On The Water Requirement Pattern Of Bingtangcheng(Citrus Sinensis Osbeck)

Most citrus in China plant in mountainous and hills with poor water and fertilizer retention capacity.Lack of water irrigation facilities coupling with frequent seasonal drought from summer to autumn result in weak water management and strong dependence on natural rainfall in China’s citrus orchards.In this study,we firstly studied the relationship between fruit size and water content of different citrus types,and then systematically investigated the physiological characteristics of branch tips,leaves and the structural characteristics of vascular bundles inside the main stems to compare the differences of water transport capacity in different types citrus.Afterward,the natural water requirement pattern of ‘Bingtangcheng’(Citrus sinensis Osbeck)was assessed by using a stem flow meter.According to the summarized water requirement pattern,the corresponding water control irrigation for‘Bingtangcheng’ was designed.The main results in this study are as follows.1.Citrus fruit size,fruit water content and juice yield are related to citrus varieties and cultivation areas.In general,the overall citrus fruit size ordered as:pomelo > sweet orange > mandarin.The water content of citrus fruit ordered as:mandarin > sweet orange > pomelo.The juice yield of citrus fruit ordered as: sweet orange > mandarin > pomelo.One citrus variety differed in fruit size,fruit juice yield and fruit water content due to their different cultivation areas.2.Citrus tree development and fruit size are related to water transportation capacity of citrus tree.Citrus fruit size and main stem thickness were positively correlated with the degree of vascularity of the tree.In this study,the vascular bundles of the pomelo trees were the most developed,showing the greatest diameter,length,density and total area of ducts,and exhibiting the greatest water transport capacity,so that the pomelo trees had the thickest main stems,fruiting branches and the largest fruit.Bigger leaf areas and more vigorous stomata developments of pomelo and‘Bingtangcheng’ showed stronger growth potential than those of Satsuma mandarin and Ponkan.3.The daily stem flow intensity of citrus trees showed a "weak-strong-weak" activity pattern: the stem flow activity was weak in the early morning,and then started at 8:00-9:00 am,reached a peak at 16:00 pm,and stopped at 18:00-20:00 pm.citrus Stem flow intensity was positively correlated with temperature and solar radiation,but negatively correlated with rainfall.citrus plant posses the highest daily stem flow intensity during flowering and fruit expansion stages,the medium daily stem flow intensity in spring shoot and young fruit stages,and the lowest daily stem flow intensity in dormancy and maturity stages.4.A precise water control treatment(controlled water supply,CWS)was designed based on the water requirement pattern obtained by stem flow,the effects of CWS group,sufficient irrigation treatment(sufficient water supply,SWS)and natural rainfall cultivation group outside the greenhouse(CK)on tree development,fruit size and quality formation of ‘Bingtangcheng’ was investigated.The results showed that adequate water supply promoted branch tip emergence and accelerated growth and development of branch tip.Due to the low water supply during fruit expansion and colour change,the leaf area index of CK trees decreased significantly and fruit growth and development were significantly inhibited,Compared with CWS group,fruit transverse diameter,longitudinal diameter and juice yield in the CK group decreased by 25.9%,25.8% and 11% respectively,and the soluble solids and acid content increased by 29.2% and 28.3% respectively.Fruit vitamin C and soluble solids content of CWS group were significantly higher than SWS group,there was no significant difference in branch tip development,flowering number,fruit shape index and fruit size with SWS group.The annual water consumption of CWS group was995.6 mm,saving 18.64% of water consumption compared with SWS group.Overall,the CWS group treatment met the normal development of ‘Bingtangcheng’ trees and fruits,and comprehensive fruit quality was better than that SWS and CK groups,with the effect of quality improvement and water-saving irrigation.