Metabolomic analysis of the roots and shoots of tomato seedlings treated with the commercial seaweed-derived biostimulant Afrikelp

Excessive fertilizer use has had severe environmental and economic consequences globally, posing a major challenge to sustainable agriculture. Biostimulants are naturally-occurring biological products that are used to enhance plant productivity by modulating metabolism. One such biostimulant is Afrikelp, which is derived from the brown alga Ecklonia maxima and is purported to enhance plant growth when applied to either the roots or shoots. However, whether a metabolic response is elicited by plants treated with Afrikelp, as well as the manner in which this biostimulant might regulate plant metabolism, has not been scientifically evaluated. In response to this, the present study used gas chromatography-mass spectrometry to explore the changes in primary metabolites between the roots and shoots of tomato (Lycopersicon esculemtum) seedlings treated with Afrikelp and those treated with water alone. Principal components analysis separated the samples treated with Afrikelp and the control, confirming a response to treatment at the metabolite level, particularly in the roots. Fold-change analysis identified many metabolites that were increased in abundance (log2 fold-change > 1.5) in both the shoot and root tissues in comparison with the control. Glycerol-3-phosphate, putrescine, and γ-aminobutyric acid were significantly differentially abundant in the root tissues treated with Afrikelp, possibly suggesting mycorrhizal colonization. In the shoot tissues, the most abundant metabolites included tryptophan, sucrose, and galactinol, and, based on pathway analysis, were largely related to energy metabolism, growth, and hormone synthesis, supporting observations that Afrikelp treatment improves crop growth. Metabolic pathway analysis further suggested the enrichment of carbon and nitrogen metabolism pathways in plants treated with the biostimulant. In summary, Afrikelp appears to increase sugar and nitrogen metabolism in the leaves of tomato plants and might encourage mycorrhizal symbiosis in the roots, thereby promoting growth.