Biostimulants are agronomic products that have become highly important in agriculture, as they are formulated with substances capable of stimulating physiological and biochemical processes in plants that help them adapt to different detrimental environmental conditions such as drought, salinity, high temperatures, nutritional deficiencies, etc. in such a way that the crops, under these conditions, maintain a good agronomic yield and quality of harvest. Every two years, the International Congress on Biostimulants is held with the aim of publicizing the most innovative and recent advances in every relevant type of product: new active ingredients, modes of action, cultivation protocols, test platforms and phenotyping, use of analytical omics tools, etc. In December 2021, the 5th World Congress on Biostimulants was held in Miami (Florida, USA). This publication summarizes the most relevant results that were presented at this congress, in which biostimulants formulated with algae extracts and amino acids stood out in a number of presentations. The various studies presented were carried out on diverse crops such as apple, blackberry, carrot, celery, cherry, corn, grape (table and wine), olive, pear, pepper, potato, rapeseed, spinach, sunflower, soybean, tomato, and wheat. The future lines of the new generation of biostimulants were also marked.

The industrial washing of corn grain during its milling generates a residue known as “corn steep liquor (CSL)”. This residue is rich in amino acids, carbohydrates, vitamins, and mineral nutrients that can stimulate the vegetative growth when applied to plants. However, the mode of action of this product is not yet known. This work involved the foliar and root application to pepper plants, at a dose of 5 mL L⁻¹, of two CSL products (CSL-H and CSL-B), which differ in the way they have been stabilized. In both cases, the size of the plants was increased, root application being more efficient than foliar. According to the studies carried out, this was because the CSL products increased the synthesis of hormones related to cell division and elongation, the net assimilation rate of CO₂, and the concentrations of the amino acids alanine, proline, and tryptophan. In addition, root application of CSL-H also increased the concentrations of arginine, isoleucine, leucine, and cysteine. These data suggest that the mode of action of these products is related to regulation, synthesis of hormones, and the stimulation of carbon and nitrogen metabolism, the CSL-H treatment being the one that produced the most changes in the amino acids analyzed.

Ultrafast energy and electron transfer as a function of solvent polarity has been demonstrated using a femtosecond transient absorption technique in a zinc phthalocyanine–benzoperylenetriimide conjugate.

Boron (B) toxicity is a relevant problem in Mediterranean regions, where irrigation water may present high concentrations of this micronutrient. In this study, the potential of aqueous extracts from the brown macroalga Laminaria digitata and the diatom Phaeodactylum tricornutum, applied alone or in combination with metalloids (Se, Si) and micronutrients (Mn, Fe, Zn), was evaluated to improve the tolerance of tomato plants (Solanum lycopersicum L.) grown under excess B (15 mg L⁻¹). The extracts were applied foliarly, and growth parameters, gas exchange, chlorophyll content, mineral composition, B accumulation, oxidative stress, and metabolic profile were analyzed. Excess B significantly reduced root development, net photosynthesis, and metabolic balance, evidencing a strong physiological impact. The application of algal extracts partially mitigated these adverse effects, mainly through improvements in photosynthesis, water use efficiency, and the accumulation of osmoprotective metabolites (proline, tryptophan, glucose). In particular, L. digitata promoted a significant increase in total biomass and greater physiological recovery compared with P. tricornutum. Conversely, formulations enriched with metalloids and micronutrients did not provide consistent additional benefits and even induced metabolic imbalances. Multivariate analysis (PCA) confirmed that relative tolerance was associated with physiological and metabolic variables rather than nutritional changes. Overall, these results highlight the potential of algal extracts, especially L. digitata, as effective biostimulants to mitigate boron toxicity in tomato.