The increasing incidence of biotic and abioticstresses resulting from climate change poses critical challenges for agricultural sustainability, driving the search for efficient biotechnological alternatives. Among these, seaweed extracts are emerging as strategic inputs due to their ability to modulate physiological and biochemical responses in plants. The objective of this study was to analyze, through a critical review, the available scientific evidence on their role in mitigating stress in crops, delving into their mechanisms of action and their productive and qualitative impacts. The methodology consisted of a systematic search of high-impact databases, selecting original studies and reviews that addressed the composition, mode of action, and agronomic effects of these biostimulants. The results show that the complex matrix of bioactive compounds in algae-including polysaccharides, phytohormones, and antioxidants regulates processes such as osmoprotection, antioxidant defense, hormonal induction,root improvement, and rhizosphere microbiota modulation, increasing yield, quality, and tolerance to adverse conditions. However, compositional variability and limited methodological standardization restrict their widespread application. In conclusion, the integration of seaweed extracts into agricultural management programs represents a promising tool for strengthening crop resilience, provided that progress is made in uniform protocols, field validation, and safety assessment.
Global climate change is leading to a continuous accumulation of greenhouse gases in the atmosphere, posing unprecedented challenges to modern agriculture. This phenomenon is increasing the incidence of environmental stresses such as drought, salinization, extreme temperatures, flooding, and desertification, making crops more susceptible to pests and diseases. Exposure to these stresses during the crop growth cycle can negatively impact yield and quality, threatening global food security. For example, sugarcane is subject to a variety of environmental stresses throughout its growth cycle. In this context, finding sustainable alternatives to mitigate the adverse effects of these stresses has become a pressing priority. Agricultural biostimulants—substances that, when applied at low doses, promote plant growth, improve nutrient use efficiency, and ultimately enhance tolerance to various abiotic and biotic stresses—have emerged as a promising strategy. Among the various biostimulant sources, seaweed extracts have attracted considerable attention for their potential to enhance crop yield and quality. These extracts are rich in a variety of bioactive compounds, including polysaccharides, polyamines, betaines, phytohormones, and antioxidants, which have positive effects on plant physiology and metabolism.
Recent studies have shown that the use of algae-based biostimulants can improve the tolerance of crops such as corn to salinity and alkalinity stress, increasing plant height, shoot and root biomass, and photosynthetic rate. Specifically, one study found that treatment with algae-based biostimulants reduced the Na*/K* ratio in both shoots and roots, thereby improving nutrient uptake and antioxidant responses in plants. Furthermore, algae extracts have been shown to promote plant growth and photosynthesis even under water stress conditions. For example, extracts from Ascophyllum nodosum have been used to increase sugarcane yield during the dry season. While knowledge regarding the applications of seaweed-based biostimulants is growing, the specific physiological and molecular mechanisms by which these extracts modulate plant responses to abiotic and biotic stresses remain incompletely understood. The role of seaweed extracts as biostimulants in stress mitigation requires further exploration of their primary mechanisms of action and evaluation of their potential as key tools for improving agricultural resilience and sustainability.
Bioactive Compounds in Seaweed Extracts and Their Physiological Effects on Plants
Seaweed extracts are considered a sustainable source of bioactive compounds and can be used as agricultural biostimulants to promote crop growth and enhance resilience to various biotic and abiotic stresses. Their chemical composition is complex and diverse, including polysaccharides, betaines, cytokinins, auxins, and phenolic compounds, which work synergistically to modulate plant physiology. The efficacy and mechanism of action of these extracts vary depending on the seaweed species, extraction method, and application conditions. Polysaccharides, such as fucoidan and laminarin, are among the most studied bioactive compounds, positively impacting seed germination and seedling growth. Algal polysaccharides have been shown to promote germination and early development in crops such as rapeseed (Brassica napus L.). Furthermore, studies have shown that the use of algal extracts can induce the expression of genes involved in plant hormone signaling, such as auxins and cytokinins, thereby promoting plant growth. Regarding stress response, algal extracts have been shown to mitigate abiotic stresses such as salinity. A study on sweet pepper (Capsicum annuum L.) under salt stress demonstrated that combining an algal extract with arbuscular mycorrhizal fungi reduced electrolyte leakage and increased crop yield. This effect was attributed to the ability of the bioactive compounds to improve plant water relations and optimize soil water retention, as demonstrated in studies using Ascophyllum nodosum extracts on lettuce (Lactuca sativa L.). The biostimulatory effects of these extracts were also associated with improved root architecture, thereby optimizing water and nutrient absorption. Studies on cannabis have shown that biostimulatory compounds containing algal extracts can alter root architecture, thereby increasing nutrient absorption. These molecular and physiological effects, including modulation of hormone signaling pathways and improved nutrient absorption, highlight the potential of seaweed extracts to enhance crop resilience to the challenges of modern agricultural environments. The figure below summarizes several quantitative effects of seaweed extracts.
Mechanisms of Abiotic Stress Tolerance Induced by Seaweed Biostimulants
Seaweed extracts play a crucial role in mitigating the effects of abiotic stress in crops by activating physiological, biochemical, and molecular mechanisms that enhance plant resilience. One of the most relevant mechanisms is osmotic regulation. Compounds such as sulfated polysaccharides, betaines, and soluble sugars present in species such as Ecklonia maxima and Ulva prolifera help maintain cellular water potential under salinity or drought conditions. These osmoregulators reduce electrolyte leakage, stabilize cell membranes, and maintain cellular turgor, thereby facilitating the continuity of essential physiological processes. Furthermore, seaweed extracts enhance the activity of key enzymes such as ascorbate peroxidase, superoxide dismutase, and catalase, promoting potent antioxidant protection. These enzymes are responsible for neutralizing reactive oxygen species (ROS) that accumulate during stress. This antioxidant effect is accompanied by metabolic reprogramming, favoring the synthesis of amino acids, sugars, and organic acids involved in cellular defense and repair. Another important mechanism is improved water and nutrient use efficiency, stemming from optimized root architecture and hormonal regulation mediated by endogenous plant hormones in the extracts, such as cytokinins and auxins. Under drought conditions, the application of marine biostimulants has been shown to reduce stomatal closure and maintain higher gas exchange rates, thereby enhancing photosynthesis and carbon assimilation. Furthermore, the interaction of seaweed extracts with the rhizosphere microbiome (e.g., the stimulating effects of compounds such as Enteromorpha polysaccharides) can stimulate the formation of beneficial bacterial communities, thereby increasing the availability of essential nutrients such as nitrogen, phosphorus, and potassium, and improving soil fertility even in the presence of soil degradation or acidification. These multifaceted mechanisms of action work together to make seaweed extracts an effective tool for enhancing crop resilience to adverse conditions, reducing the impact of stresses such as salinization, drought, and low fertility, and promoting more sustainable and resource-efficient agricultural development.
Seaweed extracts induce biotic stress defense. Seaweed extracts contain a variety of bioactive metabolites, such as sulfated polysaccharides, phenolic compounds, amino acids, and phytohormones, which act as inducers of the plant immune system, triggering defense responses against pathogens and pests. These compounds stimulate signaling pathways related to jasmonic acid (JA), salicylic acid (SA), and ethylene, promoting the accumulation of phytoalexins, pathogenesis-related proteins (PRs), and antioxidant enzymes, thereby strengthening the plant’s physical and chemical barriers. Studies with Ascophyllum nodosum extracts have shown that foliar application activates genes associated with systemic acquired resistance (SAR) and induced systemic resistance (ISR), reducing the severity of fungal and bacterial diseases in various crops. This protective effect stems from both direct effects of secondary metabolites and enhanced signaling capacity in the plant, resulting in a state of “alertness” that enables it to respond more quickly and effectively to the presence of pathogens. Similarly, liquid extracts of Ulva intestinalis and Ulva prolifera have been shown to modulate the rhizosphere microbiome, increasing the abundance of beneficial bacteria associated with the biocontrol of soilborne pathogens and improving tolerance to infection. This mechanism of inducing internal defenses and promoting beneficial interactions in the rhizosphere enhances the potential of algal extracts as sustainable tools for integrated pest and disease management. The application of algae-derived biostimulants has shown positive effects on the productivity of horticultural crops. In Diplotaxis tenuifolia L., foliar application of crude extracts of green algae, including Auxenochlorella protothecoides, Tetradesmus obliquus, and Chlamydomonas reinhardtii, and their complexes, increased fresh biomass by 27% to 32% compared to the control. This yield increase was associated with improved photosynthetic efficiency, as evidenced by higher Fv/Fm and photosynthetic performance index (PI) values, particularly in plants treated with the algae biocomposite. In basil (Ocimum basilicum L.), application of brown algae (Ecklonia maxima) extract and plant protein hydrolysate increased yield by 17.5% and 16.1%, respectively, even under water stress and nitrogen deficiency conditions. These treatments also improved water use efficiency (WP) and nitrogen use efficiency (NUE), indicating optimized physiological and metabolic processes related to plant growth.
Algal biostimulants also positively modulate crop nutritional quality. In Diplotaxis tenuifolia L., algal communities induced a temporary increase in the accumulation of antioxidant compounds such as carotenoids and phenolics, which can improve postharvest product quality. Similarly, increased nitrate accumulation was observed in leaves, reaching levels as high as 20,100 mg/kg⁻¹ 72 hours after treatment, reflecting enhanced nitrogen absorption and assimilation, as evidenced by more negative δ¹⁵N values. In basil, treatment with Ecklonia maxima extract and protein hydrolysate significantly increased the content of functional compounds such as ascorbic acid (up to +28.2%) and total phenolics (up to +14.2%). It also improved the content of volatile compounds such as eugenol, linalool, and β-cis-ocimene, which contribute to the crop’s sensory and functional qualities. The observed effects depended on the dose and type of extract used. For example, in mint, application of 50 μM gallic acid for 21 days simultaneously promoted increases in phenolic, flavonoid, and terpenoid compounds, and also induced the expression of key genes involved in menthol biosynthesis.
Conclusion
In summary, seaweed extracts are a valuable biotechnological tool for enhancing crop resilience to biotic and abiotic stresses. Their complex composition, rich in sulfated polysaccharides, polyamines, Glycine betaine, phytohormones, and antioxidants, synergistically regulates important physiological and biochemical processes, such as osmotic regulation, activation of enzymatic antioxidant systems, optimization of root architecture, and induction of key hormonal pathways. These mechanisms effectively improve crop growth, yield, and quality, even under conditions of salinity, drought, nutrient deficiency, and pathogen stress. Evidence also suggests that they can induce intrinsic defenses by activating signaling pathways related to jasmonic acid, salicylic acid, and ethylene, and modulate the rhizosphere microbiome, promoting beneficial interactions that enhance nutrient utilization and pathogen biocontrol. At the production level, the continued increase in biomass, yield, and functional compounds of high nutritional and sensory value in horticultural and aromatic crops reaffirms their potential as strategic inputs into sustainable production systems. However, due to differences in algal species, extraction methods, and application conditions, the chemical composition of extracts varies, limiting their standardization. This heterogeneity, coupled with limited molecular characterization and isolated reports of phytotoxicity in some species, highlights the need for a more systematic scientific approach to safely and effectively incorporate them into integrated crop management programs. In this regard, the development of standardized methodologies, multi-omics studies, and validation under diverse field conditions will be key steps in solidifying seaweed biostimulants as pillars of the transition to more efficient, resilient agricultural models compatible with the principles of climate-smart agriculture. Similarly, exploring combinations with other biostimulants and beneficial microorganisms (such as mycorrhizae and Trichoderma) will be crucial to enhance synergistic effects, thereby improving crop stress tolerance and optimizing resource use efficiency. Validation of these formulations must be conducted through long-term trials in conventional, organic, and agroecological production systems under diverse soil and climatic conditions, evaluating their effects on yield, quality, and soil health. Finally, detailed compatibility and phytotoxicity risk assessments for economically important species are needed to minimize potential adverse effects and ensure the sustainability of their large-scale deployment.
If you want to distribute seaweed extract or formulate them into biostimulant products to alleviate biotic and abiotic stresses on crops, Dora recommends Kelpreal from Sargassum, Alganeo from Ecklonia Maxima, and Algamax from Ascophyllum Nodosum.
