Soil mineral elements are the key factors affecting fruit quality, but which soil elements affect the sugars and organic acids of jujube fruit is still not clear. In this study, the fruit and soil of 18 major producing areas of the Tarim Basin were studied. By measuring the sugar and acid content in the fruits and element contents in the soil, the main soil mineral elements affecting the sugar and acid content in jujube fruits were identified. The results showed that the sugar components were mainly sucrose, glucose and fructose, and the organic acid components were mainly succinic acid, citric acid and malic acid. The fruits near the Kunlun Mountains had a higher ratio of sugar-to-acid and sweet-to-acid. Some elements in the soil of the Tarim Basin are abundant, such as the elements Ca, Fe, Mn and B, but the contents of the elements NO₃-N, NH₄-N, Zn and Mo are low. The contents of Ca, Mg and Mn were positively correlated with the contents of glucose, fructose and galactose. And the Fe, Ca, Mg and Mn were the main factors affecting the sugars and organic acid contents. Our study provides theoretical support for rational fertilization and efficient cultivation management of jujube.

The aim of this study was to explore the impacts of hail-proof nets with different coverage years on the environment, leaf traits and fruit quality of ‘Fuji’ apple orchards, with the expectation of providing a basis for the scientific application of the coverage years of hail-proof nets. The test results indicated that hail nets with different coverage years could reduce light intensity in the orchard and increase air humidity to a certain extent, exerting a certain positive regulatory effect on the orchard’s temperature. The laying of hail nets had no significant influence on the thickness of tree foliage but significantly enlarged the leaf area. The hail nets covered for 2 years notably enhanced the chlorophyll content and photosynthetic performance of leaves. Different coverage years of hail netting had no significant effect on the fruit weight per fruit and the fruit shape index. The fruit luster gradually diminished and was significantly lower than that of the control as the coverage years increased. Further determination of the intrinsic quality of the fruits revealed that hail nets with different coverage years had no significant impact on the fruit hardness, soluble solids and total phenolic content. However, the soluble sugar, solid/acid ratio, flavonoids and vitamin C content of the fruits covered with 2-year hail nets were significantly higher than those of the other treatments. In addition, covering the hail net for 3 years significantly reduced the percentage of the sugar core fruit rate and sugar core index, while covering the hail net for 1 year, 2 years, and not covering the hail net were more effective in maintaining the sugar core index of the fruits. A comprehensive evaluation of the principal components of the hail net treatments with different coverage years demonstrated that the 2-year hail net treatment was superior to the others. In summary, covering hail nets could improve the microenvironment of the orchard, leaf traits and fruit quality to a certain degree. When the hail-proof net had been covered for more than 2 years, its protective performance and the enhancement effect on fruit quality weakened, and it was recommended that the hail-proof net should be replaced in a timely manner.

Organic acids are crucial indicators of fruit flavor quality, but the metabolic characteristics and regulatory genes of organic acids during jujube fruit development remain largely unexplored. In this study, the cultivar ‘Heigeda’ with a high organic acid content was used as the experimental material. The organic acid content was quantified, and key candidate genes were identified through transcriptome analysis. The results indicated that malic acid and citric acid were the main organic acid content in jujube fruit and increased gradually with fruit development. Transcriptome analysis identified nine genes associated with malic acid and seven with citric acid, with four genes co-regulating malic acid and citric acid. Functional assays by transient overexpression and silencing of these four genes in the jujube fruits revealed that overexpression significantly upregulated the malic and citric acid content. However, only the silencing of aconitase1 (ZjACO1) and aconitase3 (ZjACO3) significantly downregulated the content of malic and citric acids. Therefore, aconitase1 (ZjACO1) and aconitase3 (ZjACO3) are considered the key genes that regulate the metabolism of citric acid and malic acid in jujube fruits. Our study can enrich the regulation mechanism of the organic acid metabolism of jujube fruit and provide theoretical support for the efficient cultivation of jujube fruit.