Effects of Boron Toxicity and the Application of an Extract from the Brown Alga Laminaria digitata on the Agronomic, Nutritional, and Metabolic Response of Tomato Plants

The use of unconventional water sources, such as those from marine desalination plants, is challenging for agriculture due to boron concentrations exceeding 0.5 mg L-1, which can impact crop yield and quality. To ensure sustainability, it is crucial to understand crop responses to high boron levels and to develop strategies to mitigate its toxic effects. This study evaluated the impact of irrigation with a nutrient solution containing 15 mg L-1 of boron on tomato plants (‘Optima’ variety). To alleviate boron toxicity, two biostimulant products based on an extract from the brown alga Laminaria digitata and other active ingredients were applied foliarly. Agronomic, nutritional, and metabolic parameters were analyzed, including total yield, number of fruits per plant, and fruit quality. Additionally, mineral analysis and metabolomic profiling of leaves and fruits were performed, focusing on amino acids, organic acids, sugars, and other metabolites. A control treatment was irrigated with a nutrient solution containing 0.25 mg L-1 of boron. The results showed that a boron concentration of 15 mg L-1 significantly reduced yield by 45% and degraded fruit quality. Mineral and metabolomic analyses revealed reduced Mg and Ca concentrations, increased P and Zn levels, excessive boron accumulation, and alterations in nitrogen Krebs cycle metabolism. Biostimulants did not significantly improve agronomic performance, likely due to high boron accumulation in the leaves, though its application affected the nutritional and metabolic profiles.