The Combined Application of Urea and Fulvic Acid Regulates Apple Tree Carbon and Nitrogen Metabolism and Improves Anthocyanin Biosynthesis

Agronomy Pub Date : 2024-09-09 DOI:10.3390/agronomy14092062

Laiping Wang, Ru Chen, Zhenying Jiang, Huifeng Li, Xiaomin Xue

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Abstract

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 Pn, Gs, 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.

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尿素和富马酸的联合应用可调节苹果树的碳氮代谢并改善花青素的合成

改善苹果果皮颜色一直是苹果生产的一个重要目标。为了更好地了解尿素和 FA（富勒烯酸）联合施用对花青素生物合成的调控作用和机制，分别于 2022 年和 2023 年在尿素 + FA 的五个处理（CK，仅尿素；FA50，尿素 + 50 kg ha-1 FA；FA100，尿素 + 100 kg ha-1 FA；FA150，尿素 + 150 kg ha-1 FA；FA150，尿素 + 150 kg ha-1 FA）下进行了田间试验；FA50，尿素 + 50 kg ha-1 FA；FA100，尿素 + 100 kg ha-1 FA；FA150，尿素 + 150 kg ha-1 FA；FA200，尿素 + 200 kg ha-1 FA），利用同位素（13C 和 15N）标记分析果实中碳（C）和氮（N）养分分布以及花青素生物合成的变化。我们观察到，在施用 FA 的条件下，果皮中的花青素含量在这两年都有所提高，2022 年提高了 15.98%~52.88%，2023 年提高了 15.93%~52.94%。FA150 处理的促进效果最好。除了苹果果皮中花青素生物合成相关基因和转录因子的表达水平外，研究还发现添加 FA 对花青素含量的积极影响还与叶片和果实中 C 和 N 的分布优化有关。一方面，FA 的施用不仅提高了叶片光合作用相关指标（如 Pn、Gs 和 Rubisco 活性），影响（增加）了叶片中 S6PDH、SPS 和 SS 的活性，还提高了果实糖代谢相关酶（SDH、SS-c、AI和NI）的活性，并上调果柄糖转运体（MdSOT1、MdSOT3、MdSUT1和MdSUT4）基因的表达，最终促进光合产物的合成和叶片到果实的转运，从而促进果实中13C-光合产物的积累。另一方面，脂肪酸的施用提高了叶片氮代谢相关酶（GS 和 GOGAT）的活性，优化了叶片和果实中 15N 的分布。此外，我们还观察到，施用 FA 改变了苹果园中氮肥的去向，提高了苹果树的 15NUE 和土壤中 15N 的残留量，并减少了土壤中 15N 的流失。总之，适当施用 FA150（尿素 + 150 kg ha-1）可协同优化碳和氮的养分分配，促进苹果树花青素的生物合成。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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Agronomy

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