As an agriculture microbiologist me and my team working on developing microbial products for abiotic stress mitigation. We mainly work in salinity stress alleviation in crops through microbes. We developed some microbial-based products that significantly enhance salinity tolerance in crops. In this blog, I am going to explain how microorganisms work on abiotic stress mitigation. Plant growth-promoting (PGP) microorganisms have been shown to actively induce the synthesis and increase in the levels of antioxidant enzymes, accumulation of osmolytes, and expression of different Stress-responsive genes. A variety of PGP bacteria, fungi, and actinomycetes, either individually or in the consortium form, have been demonstrated for their plan-beneficial interactions with abiotically stressed environments.

Drought tolerance:  Plant growth-promoting microorganisms such as Rhizobium, Azotobacter, Azospirillum, Pseudomonas, and mycorrhizal fungi form beneficial associations with plant roots. These PGPR can enhance plant tolerance to drought stress by producing stress-related hormones, such as abscisic acid, which regulates plant water balance and stomatal closure. They can also stimulate the development of a more extensive root system, improving water uptake by plants. Under drought stress conditions, the level of ethylene in higher plants is increased. ACC deaminase-producing microbial strains enable plant growth, by lowering the levels of ethylene. Ethylene can affect all stages of plant development such as plant tissues like roots, stems, leaves, flowers, and fruits. Microorganisms produce osmolytes, such as proline and glycine betaine, which help plants maintain cellular water potential and osmotic balance, thereby protecting them from dehydration. They also produce exopolysaccharides that bind soil particles, improving soil structure and water-holding capacity. Additionally, microorganisms can stimulate the closure of stomata, reducing water loss through transpiration. Plant growth-promoting rhizobacteria (PGPR) and mycorrhizal fungi form symbiotic relationships with plant roots. These microorganisms can improve water uptake by plants by increasing root surface area and enhancing root hair development.

Salinity tolerance: Salinity stress, caused by high soil salt concentrations, can negatively impact plant growth. Some microorganisms, particularly halotolerant bacteria, and fungi, can help alleviate salinity stress in plants. High salt concentrations can induce oxidative stress in plants by generating reactive oxygen species (ROS), which can damage cellular components. Microorganisms associated with plant roots can enhance antioxidant enzyme activity in plants, such as superoxide dismutase, catalase, and peroxidase. These enzymes scavenge ROS and protect plant cells from oxidative damage, improving plant survival under salinity stress. Microorganisms can produce osmoprotectants, such as glycine betaine, proline, and trehalose, which help plants maintain cellular osmotic balance and prevent water loss under high salinity conditions. These osmoprotectants act as compatible solutes, protecting plant cells from dehydration and maintaining cellular functions. Some microorganisms, particularly halotolerant bacteria, and fungi, have the ability to reduce soil salinity. They do so by metabolizing and transforming salt compounds, such as sodium chloride (NaCl), into less harmful forms. This salt reduction activity helps alleviate the osmotic stress caused by high salt concentrations in the soil, making it more favorable for plant growth.    

              Role of Chemical Compounds in Abiotic Stress Mitigation

Phytohormone production: Generally the majority of the auxin-producing bacteria produce IAA, while some of the other bacteria produce GA3 and other derivatives. which regulate various aspects of plant growth and development. Cytokinin-producing bacterial strains can also improve growth under drought stress. These hormones can help mitigate the adverse effects of salinity stress on plants by promoting root growth, stimulating cell division, and improving nutrient uptake. They also play a role in maintaining plant water balance and decreasing the harmful impacts of abiotic stress. Microbial gibberellin production can help plants overcome the growth inhibition caused by abiotic stresses like cold temperatures or high salt concentrations. By promoting shoot elongation and other growth processes. Microbial IAA production promotes root growth, enhances nutrient uptake, and improves overall plant vigor. These effects help plants cope with various abiotic stresses, including drought, salinity, and nutrient deficiencies. The production of these phytohormones by beneficial microorganisms helps plants modulate their physiological processes, adapt to adverse environmental conditions, and mitigate the negative effects of abiotic stresses.

Nutrient availability and uptake: Microorganisms involved in nutrient cycling and mineralization processes. Most of the nutrient cycles like Nitrogen, phosphorus, and Sulphur depend on microbial activity in the soil. They break down organic matter and convert complex nutrients into readily available forms for plants. Many microbial strains have been described in the literature for their exceptional ability to fix atmospheric nitrogen under an abiotic stress environment. Phosphate solubilization is another important trait of plant growth-promoting microbes. This trait is typically attributed to the organic acids produced by microbes as metabolic products. The enzyme phytase has also been shown to have a significant role in phosphorus mobilization. This improves nutrient uptake and utilization efficiency, facilitating plants to cope with nutrient deficiencies triggered by abiotic stresses. Microorganisms, particularly mycorrhizal fungi, form symbiotic associations with plant roots, enhancing nutrient uptake efficiency.

In conclusion, it’s important to note that the efficacy of these Microorganisms may vary dependent on the specific crop, environmental conditions, and application methods. Therefore, the appropriate selection and application of these Microorganisms should be based on scientific research and local environments. Furthermore, microbial inoculants and biofertilizers containing beneficial microorganisms have been developed to improve abiotic tolerance in agricultural systems. These products can be applied to seeds, roots, or the surrounding soil to establish beneficial microbial communities and promote abiotic resilience in crops. In my experience, very few microbial products are really working in field conditions, so check product quality and efficiency before applying them in the field.


Abiotic Stress Responses and Microbe-Mediated Mitigation in Plants: The Omics Strategies