Salinity affects the photosynthetic capacity of plants, reducing their efficiency and productivity. Therefore, it is necessary to seek alternatives to mitigate these negative effects, such as the application of biostimulants based on Ascophyllum nodosum, which can help restore photosynthetic function. This study aimed to evaluate the effects of foliar application of the biostimulant on mitigating salt stress on the photochemical efficiency of Moringa oleifera. The experiment was conducted at the Federal University of Para & iacute;ba, Areia, Para & iacute;ba, Brazil. The experimental design was a randomized block design, with four replicates and two plants per plot, with five levels of irrigation water electrical conductivity (ECw - 0.50, 1.88, 5.25, 8.62, and 10.00 dS m(-1)) and five concentrations of foliar-applied biostimulant (0.00, 1.45, 5.00, 8.55, and 10.00 ml L-1). The brackish water caused reductions in photochemical efficiency and stem diameter of moringa seedlings, with significant damage starting at an ECw of 5.25 dS m(-1). The application of the biostimulant at concentrations of 5 mL L-1 and above improved photochemical activity and growth of moringa seedlings under salt stress of up to 10.0 dS m(-1) at 60 days after sowing.

Drought is a crucial abiotic stress having a devastating effect on crops, including tomatoes (Solanum lycopersicum L.). Exogenous application of plant biostimulants and essential/beneficial nutrients is an efficient method for increasing plant tolerance and maintaining productivity under drought stress. Individual soil application of the commercial Ascophyllum nodosum seaweed extract (ASE) and potassium (K) has been widely used in alleviating drought stress in many crops. However, little information has been gained regarding the role of the integrated application of ASE and K in mitigating detrimental effects of drought stress. This study examines the combined effect of ASE and K on tomato plants on growth, fruit yield and quality, and water productivity (fruit yield [kg] per volume of water input [m(3)] throughout the growing season) under drought stress conditions. The commercial formulation of ASE was incorporated in five doses (0 [control], 1.25, 2.5, 3.75, and 5 mL L-1) along with a uniform dose of K (100 kg K2O ha(-1)) under three different soil water contents (50%, 75%, and 100% field capacity [FC]). Control plants did not receive any application of ASE or K; K applied at the same dose (100 kg K2O ha(-1)) without ASE was also included as a treatment. Poor vegetative growth, fruit yield, and physiological responses were observed with decreasing soil water content irrespective of ASE doses. Leaf area, root dry matter, fruit yield, water productivity, and membrane stability index were reduced from 26-55%, 42-58%, 53-72%, 27-48%, and 37-57%, respectively, at the lowest soil water content (50% FC) compared with 100% FC across ASE doses. Reducing soil water content to 50% FC triggered up to a 50% increase in fruit firmness and 33-67% increase in electrolyte leakage than those at 100% FC across ASE doses. Application of ASE in combination with K was effective at all doses with the highest dose of 5 mL L-1 producing up to 266% increased fruit yield, up to178% higher water productivity, up to 60% higher leaf relative water content, and up to 125% higher membrane stability index across all three soil water contents. The same dose reduced electrolyte leakage of plants by up to 48% across three soil water contents. The sole application of K resulted in a significant improvement in growth, fruit yield, and physiological traits of tomato plants. Fruit yield of plants grown with ASE (5 mL L-1) and K (100 kg K2O ha(-1)) at 50% FC was statistically similar to fruit yield of the control plants at 100% FC. Water productivity was even higher for the same treatment combinations. The same was also largely true for other growth and physiological parameters, highlighting the benefits of the integrated application of ASE and K in mitigating drought stress effects on tomato plants. An integrated program comprising ASE (5 mL L-1) and K (100 kg K2O ha(-1)) may constitute a potential beneficial strategy for tomato cultivation in water-scarce areas due to their synergistic response against drought stress.

Climate change has emerged as a challenge for soybean cultivation around the world, stimulating the development of technological alternatives that aim to mitigate the damage caused by water deficit. From this perspective, algae extract-based biostimulants have been tested to reduce water stress in several crops, but little is known about their effects on soybean. Thus, we hypothesize that a commercial biostimulant based on Ascophyllum nodosum can improve the physiological performance and water relations of Glycine max plants subjected to water deficit. To test this hypothesis, we set up an experiment in controlled conditions in a greenhouse, considering five treatments (control; application of biostimulant; water deficit (WD); WD + application of biostimulant; and WD + split application of biostimulant). The experiment was designed in completely randomized blocks with four replications per treatment and conducted in polyethylene pots containing 10 L of soil and three plants per pot. The irrigation was carried out daily; the water deficit was 50% soil moisture at field capacity, starting at the R1 stage (beginning of flowering, where there is at least one flower open at any node on the plant) and maintained for ten days. The biostimulant was applied concurrently with the onset of water deficit. We confirmed the hypothesis that foliar application of 1.0 L ha-1 of the biostimulant reduces the deleterious effects of the common water deficit at the beginning of the reproductive stage of soybean through the reduction of damage from oxidative stress (reduction of malondialdehyde synthesis by 31.2% in relation to the WD plants), maintenance of water potential and cellular homeostasis (10.2% increase in relative water content when compared with WD plants), and conservation of the contents of chlorophyll in leaves and stimulation of photosynthesis and carboxylation (68% increase in net photosynthetic rate and 49.3% increase in carboxylation efficiency in relation to WD plants). However, when applied in installments, the biostimulant was not efficient in reducing soybean water stress. Therefore, we conclude that the application of a biostimulant based on A. nodosum can help reduce the harmful effects of water deficit on soybean plants, opening up perspectives for the mass use of this extract in agricultural crops produced on a large scale.