Low molecular weight organic acid water-soluble fertilizer improves leaf photosynthesis, nutrient absorption and fruit quality of pear

Abstract:【Objective】Excessive application of chemical fertilizers for high yield causes problems such as soil compaction, acidification, and salinization in the orchard, leading to nutrient imbalance of fruit trees and decline of fruit yield and quality. With the upgrading of the fruit industry and the urgent requirements for fruit quality and efficiency, more reasonable fertilization regimes have been developed through the development of new types of fertilizers for fruit trees and the other achievements for soil health. Low molecular weight organic acids (LMWOAs), are involved in the transportation of carbon and reducing power between the cytoplasm and organelles, and are the linkers of multiple metabolic pathways in cells. Moreover, LMWOAs have strong chelating power and can form complexes with vari- ous metal ions to increase the absorption of metal ions by plants. The study aimed to detect the effects of LMWOAs in fertilizers on the growth and fruit quality in pear through evaluating pear leaf photosynthesis, nutrient absorption and fruit quality. We explored the potential of LMWOAs as a synergist for increasing the efficiency of pear fertilizers, and then determined the kind of best organic acid(s) and its optimal concentration as a synergist for fruit trees, in order to develop a new type of special water-soluble fertilizer for pears industry.【Methods】Hongbaoshi pear trees were used as experimental materials, 5% and 10% malic acid (LM and HM), citric acid (LC and HC), and oxalic acid (LO and HO) combined with NPK fertilizers were set as treatments, NPK fertilizer without additive organic acid was used as control to determine the effects of different organic acids on fruit leaf growth and photosynthetic parameters, nutrient absorption and fruit quality.【Results】Compared with the control, the LMWOAs increased the content of chlorophyll Ⅱ, and LC and HC significantly increased it by 7% and 16.6% , respectively. The LMWOAs increased the Pn (net photosynthetic rate) and WUE (water use efficiency) value. While the LO and HO increased the Pn values by 47.86% and 57.79%, and increased the WUE value by 92.63% and 127.92%, respectively. Furthermore, the leaf function score table showed that organic acid treatments could significantly improve the leaf function of pear leaves. The comprehensive scores were: oxalic acid> citric acid> malic acid. The LM, HM, LC and LO significantly increased the yield of pear and the LM increased the yield by 39.25% The coloring indexes of the peels showed that the LM significantly decreased the H° value, increased the C value, and improved fruit coloring. The HM reduced the fruit coloring. The HM, LC and HO treatments increased the fruit firmness by 9.77%, 11.40% and 12.33%l. The LM, LC and HO treatments significantly increased the total soluble sugar content of the fruits, and the highest value was obtained by the LM (22.98% higher than that of the control). The sugar-acid ratio of the LM was 18.61% higher than that of the control and 38.15% higher than that of the HC. The fruit quality scores showed that the score of the LM was the highest, while the score of the oxalic acid (LO and HO) was the lowest. The concentration of malic acid had a greater impact on fruit quality ranking. The nitrogen content in the leaves was significantly reduced by the LC. The nitrogen content in the leaves of the HC was significantly higher than those of the LO, HO and LC, while there was no significant difference between other treatments and the control. There was no significant difference in the N content of the fruits between the treatments and the control, and the N contents of the fruits of the LM, LO and HO were significantly lower than that of the HM. However, the P and K contents were both higher than those of the control, and the K content in the leaves and the fruits of the LM was significantly higher than that of the control.【Conclusion】The leaf function and fruit quality were significantly improved by malic acid, citric acid and oxalic acid. Among them, 5% and 10% oxalic acid had a better effect on promoting leaf function growth, and 5% malic acid had the best effect on improving fruit properties.