Enhancement of rice production and soil carbon sequestration utilizing nitrogen-fixing cyanobacteria

Farmland soils are currently experiencing severe degradation, with a significant decline in soil organic carbon (SOC) content. Nitrogen-fixing cyanobacteria, known for their efficient green manure properties, have considerable potential to improve soil quality. However, the underlying mechanisms driving their effects remain unclear. In this study, we utilized a nitrogen-fixing cyanobacterial strain (Anabaena azotica SJ-1), isolated from local Mollisol soil, to assess its impact on rice plant growth and to elucidate the associated mechanisms. The results indicated that Anabaena azotica SJ-1 significantly enhanced rice plant growth, particularly in low-yielding soils (dry weight of rice spikes increased by 38-74 % in high-yielding soils and 107-157 % in low-yielding soils). Soil pH, available nitrogen content, and activities of soil acid phosphatase and N-acetyl-beta-glucosaminidase were all increased with the application of Anabaena azotica SJ-1. Additionally, SOC content increased, characterized by an increase in alkyl C and a decrease in amid/carbonyl C. Moreover, the metabolic activity of live microbes in the soil was enhanced. Genome sequencing revealed that Anabaena azotica SJ-1 has a genome consisting of 6,115,153 bp nucleotides, eight plasmids, and 5367 protein-coding genes. Carbohydrate metabolism was identified as the primary metabolic pathway, while energy metabolism relied primarily on oxidative phosphorylation. This study underscores the significant potential of nitrogen-fixing cyanobacteria to improve the quality and efficiency of degraded Mollisol soils.