Biostimulants are becoming a cornerstone in the development of precision agriculture and sustainable farming.

They enhance plant resilience to stressors such as drought and temperature fluctuations while maintaining high yields. Comprised of natural ingredients, biostimulants contribute to soil health improvement and reduced chemical fertilizer use, aligning with the modern agricultural sector’s demand for environmental safety. Implementing these solutions enables farmers to adapt to climate change and ensure stable yields without harming the environment. Want to learn more about how biostimulants contribute to sustainable agriculture? Read our article for a detailed exploration of their benefits and applications.

In the quest for sustainable and climate-resilient agriculture, a diverse array of innovative strategies has emerged to bolster resilience and productivity, from harnessing biostimulants to unraveling the intricate interplay between plants and their microbiome under environmental stresses.

Modern agriculture systems are copiously dependent on agrochemicals such as chemical fertilizers and pesticides intended to increase crop production and yield. The indiscriminate use of these chemicals not only affects the growth of plants due to the accumulation of toxic compounds, but also degrades the quality and life-supporting properties of soil. There is a dire need to develop some green approach that can resolve these issues and restore soil fertility and sustainability. The use of plant biostimulants has emerged as an environmentally friendly and acceptable method to increase crop productivity. Biostimulants contain biological substances which may be capable of increasing or stimulating plant growth in an eco-friendly manner. They are mostly biofertilizers that provide nutrients and protect plants from environmental stresses such as drought and salinity. In contrast to the protection of crop products, biostimulants not only act on the plant’s vigor but also do not respond to direct actions against pests or diseases. Plant biostimulants improve nutrient mobilization and uptake, tolerance to stress, and thus crop quality when applied to plants directly or in the rhizospheric region. They foster plant growth and development by positively affecting the crop life-cycle starting from seed germination to plant maturity. Legalized application of biostimulants causes no hazardous effects on the environment and primarily provides nutrition to plants. It nurtures the growth of soil microorganisms, which leads to enhanced soil fertility and also improves plant metabolism. Additionally, it may positively influence the exogenous microbes and alter the equilibrium of the microfloral composition of the soil milieu.

According to the Agriculture and Horticulture Development Board, biostimulant products were classified into two main groups, non-microbial and microbial. Recently, Pascale et al. (2015) classified plant biostimulants based on enhancing plant nutrition into five categories including microorganisms (table 1).

Figure 1. Schematic representation of the different types of plant biostimulants and their beneficial mechanisms in plants

Plants naturally associate with many beneficial microorganisms which have key roles in host development, metabolism, stress adaptation, and health. Plant hosts can selectively attract microorganisms that provide them with a variety of essential functions to adapt their physiology and development to the local environment.

The best-known plant-growth-promoting microorganisms (PGPMs) include bacteria and fungi, but also archaea and viruses can be of benefit to plants. Microorganisms can promote plant growth through a broad range of modes and mechanisms of action. Although beneficial microbes usually display more than one of these mechanisms, they can be grouped according to their principal mode of action and therefore intended biotechnological application.

• Biofertilizers participate in the provision of nutrients to the plant. Biofertilizers are the broadest and probably best understood category of PGPMs. Nutrient acquisition facilitated by biofertilizers usually involves macroelements such as nitrogen, phosphorus, and potassium, but also microelements such as iron, zinc, copper, etc. The mechanisms include atmospheric nitrogen (N2) fixation as well as soil nutrient solubilization and mobilization.
• Phytostimulators are rhizosphere or endophyte microorganisms, fungi, and bacteria, which can influence plant growth and development by affecting plant hormone metabolism, either through the production of phytohormones such as auxins, cytokinins, and gibberellins or by interfering with plant endogenous hormone homeostasis. This type of PGPM facilitates implantation, accelerates growth, and promotes greater plant vigor, but can also mitigate the damaging effects of abiotic stresses.
• Bioprotectors are those microorganisms that participate in the induction of plant abiotic stress resistance. Several specific mechanisms have been proposed for microbe-mediated plant tolerance to stresses such as drought or salinity, including volatile compounds, alteration in root morphology, accumulation of osmolytes, exopolysaccharide (EPS) production, and antioxidant defense induction.
• Bioremediators. These microorganisms participate in the remediation of contaminated soils. Contamination of agricultural soils with heavy metals and other toxic compounds is a significant environmental problem with a strong impact on agriculture and human health. Rhizosphere microbes can significantly affect heavy metal mobility and availability to the growing plant through mechanisms such as the release of chelating agents, acidification and redox changes.
• Biocontrollers. Biocontrol Agents (BCAs) are used for suppressing plant diseases and pests. Although less extensively used, biocontrol can also be applied to suppress invasive weeds. Widely used microbial BCAs are certain rhizobacteria and fungi; however. mycoviruses and bacteriophages have the potential to control phytopathogens. Effective biocontrollers may compete with pathogens for available nutrients, but often also produce specific compounds (i.e., antibiotics, hydrolytic enzymes, volatiles) that inhibit the growth of the pathogen. Some rhizosphere bacteria and fungi can also contribute to plant immunity through activation of the so-called Induced Systemic Resistance (ISR) in the plant.

In essence, biostimulants are becoming an integral part of modern agriculture, offering environmentally friendly solutions to increase crop yield and resilience. By investing in their use, farmers not only enhance productivity but also contribute to a more sustainable future.