The role of Ascophyllum nodosum biostimulants in agriculture

In the context of global challenges such as food security, environmental pressure, and climate change, seeking efficient and environmentally friendly agricultural production materials has become a top priority. Ascophyllum nodosum, a common brown algae, and its extract-based biostimulants, with their unique bioactive components, are emerging as a sustainable solution for promoting plant growth, enhancing stress tolerance, and assisting in disease control, thus driving agriculture towards a greener and more ecological direction.

Ascophyllum nodosum Biostimulant: A Treasure Trove of Natural Active Ingredients

Ascophyllum nodosum, growing on the cold coastlines of the North Atlantic, has evolved a rich array of secondary metabolites and defense substances in the harsh intertidal environment, giving its extract diverse biological activities. Its main functional components include:

1.Natural plant hormones: such as cytokinins, auxins, and gibberellins, which synergistically regulate plant growth and development in low concentrations and multi-component forms.

2.Polysaccharides: such as alginic acid and fucoidan, which improve soil aggregate structure, retain water and nutrients, and form a protective film on the plant surface.

3.Osmotic regulators: such as mannitol and betaine, which help plants maintain cellular homeostasis under stress.

4.Polyphenols and antioxidants: which scavenge free radicals and enhance plant tolerance to oxidative stress.

5.Trace elements and amino acids: present in chelated form, making them easily absorbed and utilized by plants.

Multidimensional Mechanisms for Promoting Plant Growth

Seaweed biostimulants are not traditional fertilizers; their core function lies in “regulating” plant physiological processes and improving the efficiency of resource utilization.

1.Root System Stimulation: Stimulates root development, increases root surface area and vitality, and enhances the absorption of water and nutrients.

2.Photosynthesis Promotion: Increases chlorophyll content and photosynthetic efficiency, leading to increased carbohydrate accumulation and laying the foundation for higher yields.

3.Enhanced Nutrient Utilization: Its active ingredients activate nutrients in the soil and promote nutrient transport and distribution within the plant.

4.Quality Improvement: Multiple studies have shown that application can improve fruit sugar content, color, vitamin content, and storage life.

Systemic Enhancement of Plant Stress Tolerance: Addressing Abiotic Stress

Facing challenges such as drought, salinity, and extreme temperatures, Ascophyllum nodosum biostimulants enhance plant resilience through multiple pathways:

1.Physiological Osmotic Regulation: Inducing plants to accumulate compatible solutes such as proline and betaine, maintaining cell turgor pressure, and resisting drought and salt stress.

2.Activation of Antioxidant Defense System: Increasing the activity of key enzymes such as superoxide dismutase (SOD) and peroxidase (POD), effectively scavenging excess reactive oxygen species produced under stress, and reducing oxidative damage.

3.Stress Signal Regulation: Regulating the metabolism of stress hormones such as abscisic acid (ABA) and jasmonic acid (JA), optimizing the plant’s stress response strategy.

4.Membrane System Stabilization: Protecting the structural and functional integrity of cell membranes, reducing electrolyte leakage.

Schematic diagram illustrating the mechanism by which Ascophyllum nodosum extract alleviates salt stress

Proposed mechanisms of action of the three components (acidic, neutral, and alkaline) of Ascophyllum nodosum extract when applied to plants subjected to drought stress

Inducing Systemic Resistance: Aiding in the Control of Biotic Stress

Besides direct antimicrobial activity (such as polyphenols), its more important role lies in “awakening” the plant’s own immune system:

1.Activating Defense Signaling Pathways: Activating salicylic acid (SA) and jasmonic acid (JA)-dependent defense signaling pathways, putting the plant in a “pre-alert state.”

2.Accumulating Defense Substances: Promoting the synthesis and deposition of disease-resistant substances such as phytoalexins, lignin, and callose, building physical and chemical barriers.

3.Systemic Resistance Formation: The induced resistance can be transmitted within the plant, and even passed on to offspring, providing broad-spectrum and long-lasting protection.

4.Rhizosphere Microbiome Regulation: Shaping a rhizosphere microenvironment favorable to the growth of antagonistic bacteria, indirectly inhibiting soil-borne diseases through microorganisms.

A schematic diagram illustrating how Ascophyllum nodosum extract (ANE) induces plant defense responses against different plant pathogens

Sustainability Core Advantages and Application Practices

The sustainability of seaweed biostimulants is reflected throughout the entire process, from resource sourcing and production to application and environmental impact:

1.Renewable Resources: Seaweed grows rapidly, and sustainable utilization can be achieved through scientific rotational harvesting management.

2.Low-Carbon Production Process:  Often uses low-temperature physical or biological fermentation extraction methods, resulting in low energy consumption and minimal pollution.

3.Safe and Environmentally Friendly Use: Safe for non-target organisms, leaves no harmful residues, and contributes to the protection of agricultural biodiversity.

4.Significant Economic Benefits: Improves quality and yield, reduces the use of fertilizers and pesticides, lowers production costs, and increases the value of agricultural products.

Key Application Techniques: Can be applied through seed soaking, root dipping, foliar spraying, and soil drenching. The key is “early application” and “regular application,” focusing on prevention, especially during the seedling stage, transplanting stage, before flowering, and before encountering stress. Recommended for use in combination with organic fertilizers and microbial agents for synergistic effects.

Improving Soil Health

Soil health, also known as soil quality, is simply defined as “the capacity of soil to function as a vital ecosystem that sustains plants, animals, and humans.” Healthy soil contributes to the environmental management of the biosphere (air, water, and soil) and enhances the productivity of plants and animals in natural and artificial systems. To enhance the soil’s ability to maintain its environmental and biological functions, it needs to be improved. Research on some seaweed extracts has clearly shown that their mechanisms of action as agricultural inputs are twofold:

1. As mentioned above, they act as biostimulants, promoting crop growth and increasing yields;

2.They act as chelating agents, directly improving soil health.

Due to the alginates remaining in the hydrolyzed extract, ANE provides natural chelation to the soil, thereby increasing the availability of minerals to plants and improving soil aeration and water retention capacity.

Conclusion: Biostimulants based on Ascophyllum nodosum surpass the single-functionality of traditional inputs, empowering plants in a systemic and ecological way, and are a powerful tool for achieving multiple agricultural goals of increased yield, improved stress resistance, enhanced quality, and environmental protection. They are not only a tool to replace some chemical inputs, but also a crucial cornerstone for building a healthy agricultural ecosystem and moving towards climate-smart agriculture, representing one of the core directions for the future development of agricultural inputs.