Innovations in agriculture, including application of chemical fertilisers, have allowed food production to keep pace with the growing population. Nevertheless, this has come at a significant environmental cost. Improving plant nutrient use efficiency (NUE) is critical in tackling greenhouse gas emissions, improving biodiversity and increasing productivity in agricultural systems to meet the requirements of the growing world population. Biostimulants are compounds from various sources that can regulate plant physiological processes and increase nutrient uptake and utilisation. Consequently, integrating use of plant biostimulants with conventional agriculture may facilitate reduced fertiliser use while maintaining crop yields. Here, we discuss the current research on biostimulants in the context of improved macro- and micronutrients use efficiency. While most of the reviewed studies report a positive effect of biostimulants on NUE within the studied crop, there is a need for a more systematic approach, including precise calculations of NUE and conducting trials under both optimum and sub-optimum nutrient conditions. Overall, plant biostimulants appear to be a promising addition to sustainable agriculture practices, with multiple benefits from both social and environmental perspectives.

Eight rumen additives were chosen for an enteric methane-mitigating comparison study including garlic oil (GO), nitrate, Ascophyllum nodosum (AN), Asparagopsis (ASP), Lactobacillus plantarum (LAB), chitosan (CHI), essential oils (EOs) and 3-nitrooxypropanol (3-NOP). Dose-dependent analysis was carried out on selected feed additives using a meta-analysis approach to determine effectiveness in live subjects or potential efficacy in live animal trials with particular attention given to enteric gas, volatile fatty acid concentrations, and rumen microbial counts. All meta-analysis involving additives GO, nitrates, LAB, CHI, EOs, and 3-NOP revealed a reduction in methane production, while individual studies for AN and ASP displayed ruminal bacterial community improvement and a reduction in enteric CH₄. Rumen protozoal depression was observed with GO and AN supplementation as well as an increase in propionate production with GO, LAB, ASP, CHI, and 3-NOP rumen fluid inoculation. GO, AN, ASP, and LAB demonstrated mechanisms in vitro as feed additives to improve rumen function and act as enteric methane mitigators. Enzyme inhibitor 3-NOP displays the greatest in vivo CH₄ mitigating capabilities compared to essential oil commercial products. Furthermore, this meta-analysis study revealed that in vitro studies in general displayed a greater level of methane mitigation with these compounds than was seen in vivo, emphasising the importance of in vivo trials for final verification of use. While in vitro gas production systems predict in vivo methane production and fermentation trends with reasonable accuracy, it is necessary to confirm feed additive rumen influence in vivo before practical application.

Reduction in the greenhouse gas (GHG) emissions and nitrogen (N) pollution of ground water by improving nitrogen use efficiency (NUE) in crops has become an intensively investigated research topic in pursuit of a more sustainable future. Although, distinct solutions have been proposed there are only a few reports documenting the detailed interplay between observed plant growth dynamics and changes in plant N related transcriptional and biochemical changes. It was previously demonstrated that the application of a formulated biostimulant (PSI-362) derived from Ascophyllum nodosum (ANE) improves N uptake in Arabidopsis thaliana and in barley. In this study, the effect of PSI-362 on the growth dynamics of wheat seedlings was evaluated at different biostimulant and N supplementation rates. Wheat grown on N deficient MS medium was also analysed from the first hour of the treatment until the depletion of the nutrients in the medium 9 days later. During this time the biomass increase measured for PSI-362 treated plants versus untreated controls was associated with increased nitrate uptake, with surplus N assimilated by the biomass in the form of glutamate, glutamine, free amino acids, soluble proteins, and chlorophyll. Phenotypical and biochemical analysis were supported by evaluation of differential expression of genetic markers involved in nitrate perception and transport (TaNRT1.1/NPF6.3), nitrate and nitrite reduction (TaNR1 and TaNiR1) and assimilation (TaGDH2, TaGoGAT, TaGS1). Finally, a comparative analysis of the precision biostimulant PSI-362 and two generic ANEs demonstrated that the NUE effect greatly differs depending on the ANE formulation used.

Most vegetable crops are salt sensitive, growing inadequately in salinised soils due to the accumulation of toxic ions from prolonged irrigation regimes. Plant biostimulants are a potential tool that can be used to counteract salinity stress and increase crop yield. The aim of this study was to investigate the ability of the proprietary protein hydrolysate and Ascophyllum nodosum-derived biostimulant PSI-475 to activate salinity stress tolerance responses in plants. After characterising PSI-475 composition, initial biostimulant activity screening was performed using Arabidopsis thaliana. PSI-475 stimulated primary root growth (+5.5–20.0%) and photosynthetic pigments content (18.8–63.0%) under unstressed and salinity stressed conditions. Subsequently, PSI-475 was assessed by foliar application on tomato plants (cv. Micro-Tom) that received a saline irrigation water program, which caused a significant decrease in fruit yield (−37.5%). Stressed plants treated with PSI-475 increased this parameter by 31.8% versus the stressed control. Experimental data suggest that PSI-475 can alleviate the negative effects of saline irrigation by improving osmotic adjustment and ion homeostasis markers. PSI-475 was also able to provide significant yield benefits in unstressed plants (+16.9%) that were associated with improved leaf biochemical markers. The data presented support the use of this precision biostimulant to target the negative effects of salinity stress from irrigation.

Salinity stress is a major problem affecting plant growth and crop productivity. While plant biostimulants have been reported to be an effective solution to tackle salinity stress in different crops, the key genes and metabolic pathways involved in these tolerance processes remain unclear. This study focused on integrating phenotypic, physiological, biochemical and transcriptome data obtained from different tissues of Solanum lycopersicum L. plants (cv. Micro-Tom) subjected to a saline irrigation water program for 61 days (EC: 5.8 dS/m) and treated with a combination of protein hydrolysate and Ascophyllum nodosum-derived biostimulant, namely PSI-475. The biostimulant application was associated with the maintenance of higher K⁺/Na⁺ ratios in both young leaf and root tissue and the overexpression of transporter genes related to ion homeostasis (e.g., NHX4, HKT1;2). A more efficient osmotic adjustment was characterized by a significant increase in relative water content (RWC), which most likely was associated with osmolyte accumulation and upregulation of genes related to aquaporins (e.g., PIP2.1, TIP2.1). A higher content of photosynthetic pigments (+19.8% to +27.5%), increased expression of genes involved in photosynthetic efficiency and chlorophyll biosynthesis (e.g., LHC, PORC) and enhanced primary carbon and nitrogen metabolic mechanisms were observed, leading to a higher fruit yield and fruit number (47.5% and 32.5%, respectively). Overall, it can be concluded that the precision engineered PSI-475 biostimulant can provide long-term protective effects on salinity stressed tomato plants through a well-defined mode of action in different plant tissues.

Chitosan is a derivative of chitin that is one of the most abundant biopolymers in nature, found in crustacean shells as well as in fungi cell walls. Most of the commercially available chitosans are produced from the exoskeletons of crustaceans. The extraction process involves harsh chemicals, has limited potential due to the seasonal and limited supply and could cause allergic reactions. However, chitosan has been shown to alleviate the negative effect of environmental stressors in plants, but there is sparse evidence of how chitosan source affects this bioactivity. The aim of this study was to investigate the ability of chitosan from mushroom in comparison to crustacean chitosan in enhancing drought stress tolerance in tomato plants (cv. MicroTom). Chitosan treatment was applied through foliar application and plants were exposed to two 14-day drought stress periods at vegetative and fruit set growth stages. Phenotypic (e.g., fruit number and weight), physiological (RWC) and biochemical-stress-related markers (osmolytes, photosynthetic pigments and malondialdehyde) were analyzed at different time points during the crop growth cycle. Our hypothesis was that this drought stress model will negatively impact tomato plants while the foliar application of chitosan extracted from either crustacean or mushroom will alleviate this effect. Our findings indicate that drought stress markedly decreased the leaf relative water content (RWC) and chlorophyll content, increased lipid peroxidation, and significantly reduced the average fruit number. Chitosan application, regardless of the source, improved these parameters and enhanced plant tolerance to drought stress. It provides a comparative study of the biostimulant activity of chitosan from diverse sources and suggests that chitosan sourced from fungi could serve as a more sustainable and environmentally friendly alternative to the current chitosan from crustaceans.