Foliarly applied biochelates as an eco-friendly strategy for biofortification with iron and zinc of hydroponically grown lettuce

Agronomic biofortification is already in practice to reduce hidden hunger but its dependency on synthetic chelates raises environmental and health concerns. This study examined sustainable, peptide-based biochelates with zinc (Zn) and iron (Fe) as replacements of synthetic chelates by evaluating their effects on the growth and nutritional quality of two lettuce cultivars, Aquino and Barlack, in a hydroponic system. Although foliar treatments with peptides-based fertilizers induced no fresh shoot yield variations or a slight decrease in the case of Zn-peptide treatment, they were highly efficient in increasing leaf Fe concentration by up to 690% with Fe-peptide and leaf Zn concentration by 222% with Zn-peptide compared to the control, achieving successful biofortification in both cultivars. Tested fertilizers induced cultivar-specific shifts in primary and secondary metabolism. Aquino demonstrated an enhancement of shoot fresh weight, and fresh and dry weight of roots especially with peptide and Zn-peptide application, an increase of total amino acids and Vitamin C, and soluble carbohydrates in leaves, indicating a genotype-specific upregulation of nitrogen and carbon metabolism. In contrast, the Barlack cultivar exhibited a stronger antioxidant response, DPPH radical scavenging activity, and an increase of flavonoids and anthocyanins in leaves. Peptides-based fertilizers reduced soluble carbohydrates and total anthocyanins in both cultivar leaves, vitamin C content in Aquino leaves and amino acids content in Barlack leaves while Aquino leaves showed an increased amino acids content under peptide treatment. Zinc peptide reduced shoot dry biomass, and total phenol and antioxidant activity only in Barlack leaves. Zn-peptide and peptide treatments reduced leaf P and increased leaf B concentration in both cultivars. The findings support a targeted-biofortification framework, utilizing tailored peptide-biochelates on specific lettuce cultivars to enhance the nutritional quality of crops in a sustainable way.