Effect Of Soil Acidification On Acidity Of Lemon Fruit And Its Physiological Mechanism

In recent years,the acidification of soil in Chinese citrus orchards has increased,resulting in malnutrition of the tree and decline in fruit quality.In this paper,soil pot culture experiment with 2-year-old Yunling No.1(Astragalus rootstock)as a test material to study and analysis the effectiveness of soil acidification on soil available nutrients,content of tree nutrient,fruits quality especially sugar and acid components at different development stages of the fruit,and enzyme activities relevant to organic acid metabolism,aiming at understanding physiological mechanism of soil acidification regulating citrus fruit organic acid metabolism and accumulation,its relationship with nutrient utilization,and improving citrus orchard acid soil remediation and citrus fruit quality upgrading.The main results are as follows:1.Soil acidification significantly affected lemon fruit quality.With the increase of soil acidification degree or the decrease of soil p H,the concentrations of soluble solids and titratable acid in winter flower fruit increased significantly,but the single fruit weight and edible rate were not significantly affected;the thick peel,and soluble solids,titratable acid,Vc concentrations of spring flower fruit increased significantly,while the edible rate and juice yield decreased significantly.2.Soil acidification significantly affected the mineral nutrient content of soil,leaves and fruits.With the decrease of soil p H,the content of soil available K and available Mn increased significantly,the content of available Mg and available Ca increased firstly and then decreased.In weak acid soil(p H6),its content was the highest,the effective iron content is increased but not significant;As soil acidification increased the contents of K and Ca in winter flower fruit,spring flower fruit,and spring shoot leaves but decreased the content of Mg;increased the content of Fe and Mg in the leaves,especially when they were strongly acidic(p H 4),the K,Fe and Mn contents of the fruit also increased with a certain extent.3.The activity of organic acid-related enzymes in fruits is significantly correlated with the nutrient content of organelles.There was significant positive correlation between cytoplasmic Fe,Mg and Cyt-ACO,K and Mg were significantly positively correlated with PEPC,indicating that the increase of cytoplasmic Fe and Mg promoted the degradation of citric acid,and K and Mg increased the synthesis capacity of citric acid in the cytoplasm;Mg in mitochondria had significant positive correlation with CS,while K and Fe had significant positive correlation with Mit-ACO,indicating that the increase of content of Mg in the mitochondria promoted the synthesis of citric acid,whileK and Fe increased Mit-ACO activity and degraded citric acid.4.Soil acidification significantly affected fruit organic acid metabolism and its relationship with nutrient utilization.Soil acidification significantly increased the content of citric acid and promoted the accumulation of malic acid in winter flower fruit;With the increase in soil acidification,Mg of cytoplasm and mitochondria decreased,the activity of CS and PEPC was decreased,and citric acid synthesis was inhibited;As soil acidification increased,the content of Fe and Mg in the cytoplasm decreased,and the activity of Cyt-ACO and the degradation ability of citric acid were increased,resulting citric acid to accumulate in large amounts especially at strong acidity(p H 4).