# Broad Target Metabolomics Revealed the Key Regulatory Mechanisms of the Effects of Trace Element Water-Soluble Fertilizer on the Growth of Corylus heterophylla × Corylus avellana Seedlings

## TL;DR

This study shows how trace element water-soluble fertilizer affects hazelnut seedlings by boosting flavonoid production and gene activity, promoting growth.

## Contribution

The study identifies specific flavonoid metabolites and genes influenced by trace element fertilizer in hazelnut seedlings.

## Key findings

- Flavonoid metabolic pathway was significantly enriched in all fertilizer treatments.
- Application of trace element fertilizer increased flavonoid content and gene expression like PAL and C4H.
- DWF4 treatment showed the most significant enhancement in flavonoid-related metabolites and gene activity.

## Abstract

Background: Scientific and rational fertilizer management can not only improve the yield and quality of hazelnut (Corylus heterophylla × Corylus avellana) but also reduce the negative impact on the environment. Methods: Liquid Chromatography–tandem Mass Spectrometry (LC-MS/MS) technology was used to reveal the contents of various metabolites in hazelnut seedlings, and differential metabolites were screened by principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). Results: The results showed that a total of 178 up-regulated differential metabolites (Fold change > 1) and 175 down-regulated differential metabolites (Fold change < 1) were detected in 6 comparison groups (DWF0 vs. DWF4, DWF0 vs. DWF5, DWF0 vs. DWF6, DWF4 vs. DWF5, DWF4 vs. DWF6, DWF5 vs. DWF6). Interestingly, the flavonoid metabolic pathway was dramatically enriched, and it was involved in each fertilization combination. The metabolites of the flavonoid pathway in different fertilized and unfertilized groups were compared and analyzed, which displayed that metabolites tricetin, eriodictyol, garbanzol, apigenin, and biochanin A were significantly up-regulated, while garbanzol and astraglin were significantly down-regulated. More interestingly, the determination of flavonoid content and real-time fluorescence quantitative polymerase chain reaction (qRT-PCR) displayed that the application of trace element water-soluble fertilizer could significantly enhance the flavonoid content and the expression of genes related to the flavonoid biosynthesis pathway, such as phenylalanine ammonia-lyase (PAL) and cinnamate 4-hydroxylase (C4H), with the DWF4 treatment displaying the most significant values. Conclusions: Overall, the application of trace element water-soluble fertilizer (especially the DWF4 treatment) markedly affected the changes in key metabolites of the flavonoid pathway and the expression levels of key genes, thus promoting the growth and development of the hazelnut, which offers an important starting point for future analysis through genetic engineering.