Effects Of Potassium Fertilizer On Photosynthetic Characteristics Of Grape Leaves And Fruit Quality

Grape is a ’potassium crop’.Potassium is an important basis for grape growth and development and improving fruit quality.There are great differences in potassium content in grape producing areas in China.Potassium deficiency is common in vineyards in China.At the same time,there are many orchards with unreasonable application of potassium fertilizer.In this study,two table grape varieties ’Summer Black ’and ’Red Globe’ and two wine varieties’Merlot’ and ’Cabernet Sauvignon’ were used as materials.The effects of potassium sulfate application on leaf photosynthetic characteristics and fruit quality of four varieties were studied in 2020 and 2021,and the effects of foliar spraying potassium sulfate on leaf photosynthetic characteristics and fruit quality of ’Summer Black’ and ’Red Globe’ were studied in 2021.The effects of soil potassium fertilizer on the peel metabolites of ’Red Globe’during maturity were analyzed.The results are as follows:（1）After applying potassium fertilizer in soil,the SPAD value of leaves of the four grape varieties was higher than that of the control at the end of color conversion,and the net photosynthetic rate of leaves increased significantly at the end of 2021.During fruit ripening,the potassium content in leaf,peel and pulp of Merlot’ increased significantly;the content of soluble solids and sucrose in fruit increased,especially in fresh varieties,and the soluble protein content in peel increased.The color of ’Red Globe’ and ’Cabernet Sauvignon’ changed earlier,and the contents of total phenols and flavonoids in the peel of ’Red Globe’ increased in 2021 and mature stage.Under the recommended amount of fertilizer application,the effect of soil potassium fertilizer on ’Red Globe’ was greater than that on the other three varieties.（2）The effect of foliar spraying potassium fertilizer on table grape was similar to that of soil application of potassium fertilizer,the photosynthetic capacity of leaves increased,the content of sugar in pulp increased,the content of acid decreased,and the contents of soluble protein,anthocyanin,total phenols and flavonoids in peel increased,but the degree of effect was less than that of soil application of potassium fertilizer.According to the principal component analysis,the comprehensive evaluation ranking of the four treatments and controls of the two varieties were as follows:spraying 8 g/L K2SO4 at the initial stage of color conversion>spraying 4 g/L K2SO4 at the initial stage of color conversion>spraying 4 g/L K2SO4 at fruit expansion stage>spraying 8 g/L K2SO4 at fruit expansion stage>no spraying.（3）A total of 436 phenolic metabolites were identified in the peel of ’Red Globe’ through extensive targeted metabonomic analysis,and 147 differential metabolites affected by potassium fertilizer were screened,of which 103 were up-regulated and 44 down-regulated during treatment.Among the differential metabolites,flavonols and phenolic acids were the most.In the treatment,most of the flavonoid differential substances were up-regulated,the number of phenolic acids up-regulated and down-regulated in non-flavonoid differential substances were similar,and stilbene were mainly down-regulated.