Ru Chen

Improving apple peel color has been an important objective in apple production. To better understand the effect and mechanism of the combined application of urea and FA (fulvic acid) regulation of anthocyanin biosynthesis, a field experiment was performed in 2022 and 2023, respectively, under five treatments of urea + FA (CK, urea only; FA50, urea + 50 kg ha⁻¹ FA; FA100, urea + 100 kg ha⁻¹ FA; FA150, urea + 150 kg ha⁻¹ FA; FA200, urea + 200 kg ha⁻¹ FA), using isotope (¹³C and ¹⁵N) marking to analyze the changes in carbon (C) and nitrogen (N) nutrient distribution as well as anthocyanin biosynthesis in fruits. We observed that, under FA application conditions, anthocyanin content in the peel was elevated in both years, with increases of 15.98~52.88% in 2022 and 15.93~52.94% in 2023. The best promotion effects were observed under FA150 treatment. Apart from the expression levels of anthocyanin biosynthesis-related genes and transcription factors in the apple peel, this positive effect on anthocyanin content induced by FA addition was also found to be associated with the optimization of C and N distribution in leaves and fruits. On the one hand, the application of FA not only enhanced leaf photosynthetic-related indexes (such as P_n, G_s, and Rubisco activity) and influenced (increased) S6PDH, SPS, and SS activities in leaves, but also elevated fruit sugar metabolism-related enzyme (SDH, SS-c, AI, and NI) activity and upregulated fruit stalk sugar transporter (MdSOT1, MdSOT3, MdSUT1 and MdSUT4) gene expression, which ultimately promoted the synthesis and the leaf to fruit transport of photosynthates, thus promoting ¹³C-photosynthate accumulation in fruits. On the other hand, FA application elevated leaves’ N metabolism-related enzyme (GS and GOGAT) activity and optimized ¹⁵N distribution in leaves and fruits. Moreover, we also observed that FA application altered the fate of N fertilizer in apple orchards, showed an elevation in apple tree ¹⁵NUE and soil ¹⁵N residuals and showed a decrease in soil ¹⁵N loss. In summary, the appropriate application of FA150 (urea + 150 kg ha⁻¹) synergistically optimized C and N nutrient distribution, and promoted anthocyanin biosynthesis in apple trees.

Seaweed extracts, which are naturally degradable and environmentally friendly, have become important components of organic fertilizers for fruit. In this study, the effects of seaweed-extract-based organic fertilizers on the levels of mineral elements, sugar–acid components, and hormones in ‘Fuji’ apples were evaluated. Eleven-year-old ‘Fuji’ apple (‘Yanfu 3’/M9/Malus robusta) trees were sprayed with seaweed-extract-based fertilizers SE1 (contained ≥20 g/L of algal polysaccharides, ≥100 g/L of amino acids, and ≥30 g/L of EDTA-Ca) and SE2 (contained ≥100 g/L of algal polysaccharides, ≥160 g/L of Ca, and ≥10 g/L of Mg) from early May to early October at two-week intervals in 2020. Water spraying was used as a control treatment. The preliminary results showed that SE1 and SE2 significantly increased the net photosynthetic rate, chlorophyll content and Rubisco enzyme activity in ‘Fuji’ apple leaves. SE1 and SE2 improved the quality of ‘Fuji’ apples. Compared to the single-fruit weight, soluble solid content (SSC), soluble sugar content, sugar–acid ratio, vitamin C (VC) content, and free amino acid content of control apples, those of SE1-treated and SE2-treated apples increased by 10.74% and 8.94%, 12.16% and 9.76%, 21.96% and 11.90%, 45.12% and 28.55%, 56.12% and 47.96%, and 17.15% and 13.42%, respectively. SE1 and SE2 significantly improved the levels of fructose, glucose, sucrose, and sorbitol, but decreased the levels of malic acid, oxalic acid, and tartaric acid in ‘Fuji’ apples. Meanwhile, SE1 and SE2 increased the levels of potassium, calcium, magnesium, iron, zinc, and boron in ‘Fuji’ apples. SE1 and SE2 significantly improved the levels of indole-3-acetic acid, zeatin riboside, and gibberellic acid, but significantly decreased the level of abscisic acid in ‘Fuji’ apples. In conclusion, spraying seaweed-extract-based foliar fertilizer is beneficial to the nutrient accumulation and flavor development in ‘Fuji’ apples.

The frequent and massive use of pesticides has led to pesticide residues in apricot, threatening food safety and human health. A reliable and simple modified QuEChERS method with ultra-performance liquid chromatography-tandem mass spectrometry was developed for the simultaneous determination of 11 pesticides in apricot. Method validation indicated that satisfied linearity (R² ≥ 0.9959), accuracy (recoveries of 72–119%), sensitivity (limits of detection, 0.03–0.30 μg/kg; limits of quantification, 0.13–1.00 μg/kg), and precision (relative standard deviations ≤ 11.9%), and matrix effects were 0.89–1.13. Apricot samples from different ecological regions in China were collected and tested using the proposed methods. Monitoring results were used to assess the dietary intake risk of Chinese populations of different ages and genders. Dietary risk assessment revealed that the risk quotients were 0.003–1.184% for different gender and age groups in China, indicating none unacceptable public health risk for general population. This work was thus significant in developing a simpler, more efficient and economical analysis method and food safety risks of the 11 pesticides on apricot and facilitated the establishment of maximum residue limits.

An analytical method that combined large-volume solid-phase (Cleanert-PEP) extraction with ultra-performance liquid chromatography-tandem mass spectrometry (SPE-UPLC-MS/MS) was established for the detection of atrazine, atrazine metabolites, and topramezon residues in environmental water. The results showed that atrazine, its metabolites, and topramezon had a good linear relationship within the linear range of 0.5–50 μg/L, and the linear correlation coefficients of all compounds were r² ≥ 0.9989. At three spiked levels of 10, 100, and 1000 ng/L, the relative recoveries rate was between 77.1% and 114.1%, with relative standard deviations (RSDs) between 0.9% and 6.8%. The limits of detection (LODs) and limits of quantification (LOQs) of all target compounds were between 0.4 and 3.0 ng/L, and between 1.2 and 10.0 ng/L, respectively. After optimisation, Cleanert-PEP was selected for pretreatment of environmental water, and its elution curve was studied, and the optimal elution volume was 6 mL. The analysis method was applied to surface water bodies around Tai’an City in Shandong Province, China, and none of the target metabolites were detected. This method has the advantages of high sensitivity, good stability, simple operation, and high efficiency. It can be used to quantify topramezon, atrazine, and atrazine metabolite residual in water samples and to investigate their behaviour in environmental water.