Biostimulants are substances or microorganisms that, when applied to seeds, crops, or the rhizosphere, stimulate natural growth processes, thereby enhancing or promoting nutrient uptake, fertilizer use efficiency, tolerance to abiotic stress, or improving crop quality and yield.

Biostimulants are considered an environmentally friendly alternative, as they can perform some of the functions of traditional fertilizers while minimizing negative impacts on ecosystems. Unlike fertilizers, which directly supply nutrients, biostimulants act through a "non‑nutritional dependence" mechanism – they function as stimulants rather than as suppliers of mineral nutrients.

Non‑microbial biostimulants

1. Humic acids. Humic acids are high‑molecular‑weight organic compounds formed from plant and animal residues through microbial decomposition and transformation. They are widely found in soil, peat, lignite, and other materials. They possess strong ion‑exchange and adsorption capacities. On one hand, they can chelate heavy metal ions in the soil, reducing heavy metal toxicity; on the other hand, they can adsorb nitrogen, phosphorus, and potassium nutrients in the soil, reducing nutrient loss and improving fertilizer efficiency. They also stimulate root growth and enhance plant stress tolerance. Application of humic‑acid‑based fertilizers can effectively improve saline‑alkali soils, lower soil pH, ameliorate soil physicochemical properties, promote crop growth, and thus bring about better economic returns.

2. Seaweed extracts are substances extracted from seaweeds that are rich in natural active ingredients, including mainly seaweed polysaccharides, plant hormones, phenolic compounds, and trace elements. Seaweed polysaccharides can strengthen plant cell walls and improve stress resistance; plant hormones such as auxins and cytokinins regulate plant growth and development; phenolic compounds possess antioxidant and antimicrobial activities. Research shows that seaweed extracts can promote root growth and development, increase germination rates, and enhance plant defense against drought, salinity, and other adverse conditions. In horticultural crop production, applying seaweed extracts as foliar sprays can improve the quality and yield of horticultural crops.

3. Amino acids are the basic units of proteins and also important plant growth regulators. Amino acids can be directly absorbed and utilized by plants, participating in the synthesis of biological macromolecules such as proteins and nucleic acids; they promote the synthesis of plant hormones and regulate growth; they have chelating effects on metal ions, thereby improving plant uptake and utilization of micronutrients. Amino acids have a significant effect on increasing fruit yield, fruit number, and fruit weight.

4. Chitosan is a product of chitin deacetylation and belongs to natural cationic polysaccharides. It can induce systemic acquired resistance in plants, trigger plant defense responses, and enhance disease resistance. It also regulates plant growth and development, promotes both root and shoot growth, and can improve the structure of soil microbial communities by increasing the abundance of beneficial microorganisms.

Microbial biostimulants mainly consist of beneficial microorganisms such as mycorrhizal fungi, rhizobia, and Bacillus spp. Mycorrhizal fungi and rhizobia form symbiotic relationships with plants, or exert direct effects on plants, thereby regulating plant growth, development, and physiological activities.

Biostimulants, by inducing the plant’s own regulatory networks and rhizosphere microecology, promote modern agricultural production, effectively resist various stress conditions, and improve quality and yield. In the future, by leveraging multi‑omics platforms, phenomics platforms, and intelligent tools and equipment, we will dissect their complex interaction modes, discover environmentally friendly products and precision green targeting tools, and advance applications in organic agriculture, desert agriculture, and other complex field conditions, contributing to a “more efficient,” “greener,” and “more sustainable” global agriculture.