Effects Of Shading On Leaf Photosynthetic Characteristics And Fruit Quality Of Granny Smith Apple

Granny Smith is one of the high-acid apple varieties,rich in organic acids and vitamin C,and has excellent storage stability.It is an excellent raw material for concentrated juice.Ningxia,as one of the growing areas of Granny Smith apples,may be due to the high light intensity in the local cultivation conditions,resulting in poor fruit quality of high-acid apples,insufficient acid content and low fruit juice yield.This study took Ningxia Granny Smith as the research object,and set up a green apple tree shading test in the orchard of Hedong Village,Dazhan Town,Zhongning County.The 35%shading treatment and the real shading treatment(bagging)of the Granny Smith apples were used as controls to carry out experimental research.Through the detection and analysis of the photosynthetic characteristics of Granny Smith leaves with different shading intensities,the effect of different shading treatments on the photosynthetic characteristics of Granny Smith leaves was studied.To explore the effects of different shading treatments on the quality of Granny Smith apples;to provide a theoretical reference for improving the cultivation measures of Granny Smith apples,and to provide a scientific basis for optimizing the industrial layout of Granny Smith apples in Ningxia.The main results are as follows:1.15%shading treatment increased the chlorophyll content of Granny Smith,while more than 25%shading treatment significantly decreased the chlorophyll content,and chlorophyll a/b first decreased and then increased with the increase of shading degree.15%shading treatment weakened the phenomenon of’photosynthetic lunch break’ in Granny Smith leaves,and more than 25%shading treatment changed the photosynthetic diurnal variation from ’double-peak’ to ’ single-peak’,but 35%shading made the photosynthetic rate significantly reduce.The phenomenon of’photosynthetic lunch break’ is obviously related to the drop of stomatal conductance at noon.Shading reduces plant light compensation point,light saturation point,dark respiration rate and quantum efficiency.2.With the increase of shading degree,the maximum fluorescence value of Granny Smith leaves increased.Shading improves the absorption capacity of leaves to light energy,but reduces the activity of photosystem Ⅱ reaction center,shading inhibits the reduction ability of QB of photosystem Ⅱ and improves the reduction ability of QA;improves the quantum ratio of PS Ⅱ for electron transfer,and reduces the reduction of QA.Heat dissipation quantum ratio to improve light energy utilization,3.Different shading treatments had obvious effects on the real longitudinal diameter,transverse diameter and single fruit weight of Granny Smith apples.Shading will delay the appearance of the maximum vertical and horizontal diameter of the fruit.Under different shading treatments,the shading rate of 15%has little effect on the fruit,and the shading rate of more than 25%will reduce the growth rate of fruit per fruit weight,which will obviously delay the growth and development of longitudinal and transverse diameters.When the shading rate reaches 35%,will significantly affect the fruit size and single fruit weight at harvest,thereby affecting the total yield of Granny Smith apples.4.Under different shading treatments,there was no significant difference in the shape index of green apples;shading made the fruit surface of the green apples uniform in color,reduced the peeling hardness of the fruit,and had better palatability.Shading reduces the anthocyanin content of the peel.Acid is an important quality factor of Granny Smith apple.Moderate shading of the fruit in the middle stage of fruit development is beneficial to the accumulation of total acid content and increase its vitamin C content,but it will reduce the content of soluble total sugar and total phenols in the fruit.Under the shading treatment,the content of quinic acid and shikimic acid in Granny Smith increased,but it was not conducive to the accumulation of acetic acid and lactic acid.The shading rate of less than 15%increased the content of Granny Smith malic acid,and the shading rate of less than 25%increased the content of Granny Smith lemon.The acid content increases;at the same time,fruit bagging is beneficial to the increase of total acid,malic acid,acetic acid,lactic acid,quinic acid,shikimic acid and citric acid content,maintaining the total phenolic content and sugar content of the fruit,and promoting the accumulation of vitamin C,to improve the inner quality of Granny Smith apples in all aspects.In summary,the adaptation range of Granny Smith to light intensity is narrow;through moderate shading,the adjustment mechanism of Granny Smith increases the distribution ratio of energy in electron transfer,thereby improving the utilization rate of light energy by plants;15%shading is beneficial to the improvement of photosynthetic rate,and light shading of Granny Smith apple trees is beneficial to maintain higher photosynthetic rate and water utilization rate of leaves.It can effectively improve the appearance quality of green apples,reduce fruit firmness,and improve the quality of fruit products;bagging can effectively maintain the total phenolic and sugar content of the fruit while improving the internal quality of the fruit.