Fulvic Acid (FA) for Enhanced Nutrient Uptake and Growth: Insights from Biochemical and Genomic Studies

Potassium (K), one of the essential elements required for plant growth and development, determines leaf quality in tobacco (<i>Nicotiana tabacum</i> L.). Potassium (K) levels are relatively high in black soils (vertisols), but K uptake is severely hindered by the presence of remarkably high levels of calcium and magnesium. Our major objective was to enhance potassium uptake in black soils, which cover the major tobacco growing regions of Andhra Pradesh, India. Among several agronomic inputs such as soil amendments, fertilizer application, and plant growth regulators, we found that foliar application of fulvic acid (FA), one of the most bioactive humate molecules, enhanced K levels in leaves. Using next-generation sequencing (NGS), we identified changes in expression levels of a number of genes related to metabolic pathways implicated in plant growth and nutrient uptake upon FA application. Interestingly, starch levels in leaves were reduced concomitant with an increase in K attributable to FA application. We attempt to provide plausible reasons for these observed FA-induced changes. Our results suggested that FA acts in a manner similar to the plant hormone auxin in tobacco, influencing expression of key genes encoding transporters and enzymes involved in K uptake and starch metabolism. While fulvic acid has beneficial effects on plant growth, its mechanism of action is still unclear.

钾（K）是植物生长发育所必需的元素之一，同时也是决定烟草（*Nicotiana tabacum* L.）叶片品质的关键因子。黑土（vertisols）中钾元素含量相对充足，但土壤中极高的钙、镁含量会严重阻碍烟草对钾的吸收。本研究针对印度安得拉邦主要烟草种植区的黑土分布区域，旨在提升该类土壤中烟草的钾素吸收效率。在土壤改良剂、肥料施用、植物生长调节剂等多种农艺调控手段中，我们发现叶面施加黄腐酸（fulvic acid, FA）——一类生物活性最强的腐植酸分子——可有效提升烟草叶片的钾素含量。通过下一代测序（next-generation sequencing, NGS）技术，我们鉴定得到黄腐酸施加后，一系列参与植物生长与养分吸收代谢通路的基因表达水平发生了显著改变。值得注意的是，施加黄腐酸后，烟草叶片的钾素含量提升的同时，淀粉含量也随之下降。本研究尝试对黄腐酸诱导产生的上述变化提出合理的解释机制。研究结果表明，黄腐酸在烟草中发挥着类似植物生长素的调控作用，通过影响参与钾素吸收与淀粉代谢的关键转运蛋白编码基因及酶类基因的表达，实现上述生理效应。尽管黄腐酸对植物生长具有明确的有益作用，但其具体的作用机制仍有待进一步阐明。