Combined application of nitrogen-fixing cyanobacteria enhances rice growth and nutritional quality in saline environments

Abstract

Saline soils severely affect rice cultivation due to salt stress and reduced fertility. This study investigates the potential of Anabaena azotica and Tolypothrix tenuis (nitrogen-fixing cyanobacteria) to improve the growth and quality of rice in saline environments. Potting experiments were conducted to monitor rice growth indices including plant height, chlorophyll content, and leaf area index, which are physiological parameters at all major reproductive stages (Tillering, Tasseling, and Maturity), and assessed post-harvest rice quality. The results showed that the application of cyanobacterial treatments, particularly the combination of the two species, significantly improved the physiological growth indices and overall quality of rice. Notably, under the combined treatment, plant height and leaf total chlorophyll content increased by 4.42 % and 19.46 %, respectively, compared to the control. At the early stage of transplanting, malondialdehyde (MDA) content in the treatment group with nitrogen-fixing cyanobacteria was 40.01 % lower than that of control. However, the activities of peroxidase (POD) and catalase (CAT) were significantly increased, which indicated improved stress tolerance. The nutritional quality improved due to higher protein content and increased levels of essential amino acids such as leucine, phenylalanine, lysine, and arginine. Conclusively, nitrogen-fixing cyanobacteria are a promising, green, and sustainable method for improving rice growth and quality in saline soils. The application of cyanobacteria can partially replace chemical fertilizers and restore soil health. This helps reactivate crop production capacity in degraded lands and provides an effective way to improve agricultural sustainability and resilience.