Identifying microbes that can boost plant growth in saline soils
Plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms that live in soil adjacent to the roots of plants, as well as on root surfaces and inside root tissues. There is increasing recognition that these organisms can help provide plants with the necessary elements they need for growth, in a similar way to mineral fertilisers. “For example, PGPR can fix nitrogen from the air and decompose proteins,” explains NitroFixSal (N fixing bacteria from extreme environments as a remedy for nitrogen deficiency in saline soils) project coordinator Agnieszka Kalwasińska from Nicolaus Copernicus University in Poland. “This supplies the soil with ammonium.” PGPR also produce phytohormones that stimulate plant development, and enzymes that are able to decompose fungal cell walls, protecting plants against pathogens.
Reducing mineral fertiliser and pesticide use
There is significant opportunity to reduce the use of mineral fertilisers and pesticides by exploiting the potential of these naturally occurring bacteria. To be successful at a commercial scale however, scientists need to be able to identify and isolate bacteria species with sufficient survival rates, and use amounts that suit both the soil type and the plant species. This could be important for both economic and environmental reasons. Prices for chemical fertilisers – including ammonium nitrate, phosphorus and potassium – have increased sharply due to the rising cost of natural gas. Meanwhile, the EU is obliged to reduce the use of these fertilisers in order to meet its green objectives. “In the NitroFixSal project, we took bacteria with PGPR properties from extreme saline environments,” says Sweta Binod Kumar, a biotechnologist who also worked on the project. “This is because microorganisms naturally adapted to high-salinity conditions can better promote plant growth under salt stress, and contribute to increased plant biomass and protection against pathogens.” The PGPR strains that the project team extracted underwent extensive investigations in order to characterise their PGPR properties. The strains were applied as biostimulants, to improve the germination of wheat in laboratory conditions. “The next step involved a field study, in which selected strains were applied to non-sterile soil,” adds Kalwasińska. “Finally, the interactions between bacteria and wheat plants were investigated using advanced molecular methods. This enabled us to better understand the mechanisms of their action.”
Identifying potential biofertiliser candidates
The NitroFixSal project successfully demonstrated that saline environments are a valuable source of nitrogen-fixing bacteria with various plant growth-promoting potential. Several new strains were characterised. Two bacterial strains were shown to significantly mitigate salt stress in cereals. One of these has since been submitted to the Polish Collection of Microorganisms. Two patents of the isolate, together with its growth promotion effects on wheat, are ready to be submitted to the Polish Patent Office. “These isolated PGPRs are now potential candidates for biofertilisers,” notes Kalwasińska. “These could eventually benefit in particular farmers facing yield loss of their crops due to high-salinity conditions of the soil.” Data generated from the project will also help researchers to better understand plant-PGPR interactions at the molecular level. Researchers hope to unravel lesser-known plant growth activity, which could lead to the development of new biostimulator formulations and tools for designing new breeding strategies. “Our project very much aims to contribute towards sustainable agriculture,” says Kalwasińska.
Keywords
NitroFixSal, bacterial, rhizobacteria, nitrogen, saline, soils, fertilisers, enzymes, PGPR