Respiratory mechanism of calcium magnesium foliar fertilizer in alleviating sugar-dropping in Feizixiao litchi pulp

【Objective】The effects of spraying the calcium and magnesium foliar fertilizer on the respiration rate of Feizixiao litchi pulp glycolysis（EMP）-tricarboxylic acid cycle（TCA）pathway was explored to provide reference for litchi planting.【Method】 During the period of fruit development，crowns of Feizixiao plants were sprayed with 0.3% magnesium chloride（Mg）， 0.3% calcium chloride（Ca）and 0.3% CaCl₂+0.3% MgCl₂（Ca+Mg），and water as control（CK）， indicators of pulp flavor and quality at different developmental stages， the dynamic changes of EMP-TCA pathway respiration rate and key enzyme activities were detected and compared.【Result】 The soluble sugar content of litchi pulp showed an upward trend from 35 to 56 d. After 63 d after flowering， except for the soluble sugar content of pulp treated with Ca+Mg did not decrease significantly（P>0.05， the same below）， and sugar withdrawal occurred in all other treatments. The titratable acid content of all treated pulp did not change significantly before and after the harvest period，and there was no significant difference between them. The respiration rate of EMP pathway of Ca treatment and Ca+Mg treatment was significantly lower than that of Mg treatment and CK （P<0.05，the same below）， while the respiration rate of TCA pathway in Ca+Mg treatment was significantly lower than that of Ca treatment， so Ca+Mg treatment inhibited the total respiration rate of pulp by inhibiting EMP-TCA respiration rate. Around the harvest time，the activities of phosphate hexose isomerase（GPI），succinate dehydrogenase（SDH）and malic enzyme（NADP-ME）treated with Ca+Mg were significantly lower than those treated with CK. Ca treatment inhibited GPI activity and promoted PDC activity；the activity of NADP-ME in Ca treatment and Mg treatment was significantly higher than that in Ca+Mg treatment and CK.【Conclusion】In conclusion，Ca+Mg treatment inhibits the EMP and TCA pathways by inhibiting the GPI，SDH and NADP-ME activities of the pulp of Feizixiao litchi，thereby reducing the aerobic respiration rate of EMP-TCA and reducing the respiration loss of sugar in the pulp，thereby alleviating the sugar-dropping of the pulp.