Optimizing Cyanobacterial Biomass for Soil Restoration: Nutrient Enrichment and Microbial Modulation in Degraded Grasslands of Hulun Lake.

The organic and active substances released from cyanobacterial decomposition have a positive effect on improving soil quality and promoting plant growth. However, the mechanism of its influence remains unclear, particularly regarding its impact on grassland soil. The study was conducted in the periphery of eutrophic Hulun Lake using a gradient amendment experiment (0%, 3%, 5%, 10% cyanobacterial biomass) on adjacent degraded grassland soils. This design aimed to assess the effects of cyanobacterial inputs on soil physicochemical parameters and microbial community restructuring. Quantitative analyses revealed significant nutrient enrichment, with available phosphorus (AP), available potassium (AK), and nitrogen pools demonstrating differential responses. Nitrogen species exhibited the most pronounced enrichment: total nitrogen (TN) increased by 26.21%, ammonium nitrogen (NH₄⁺-N) by 41.99%, and nitrate nitrogen (NO₃⁻-N) by 54.96% relative to controls. Concurrently, stoichiometric ratios displayed dose-dependent modulation: the total organic carbon to total nitrogen (TOC/TN) ratio decreased by 3.85% under 5% biomass treatment, whereas TOC/AP and TN/AP ratios increased by 13.23% and 18.03%, respectively, indicating altered carbon-phosphorus-nutrient coupling dynamics. Additionally, cyanobacteria enhanced the alpha diversity of the soil bacterial community without altering its overall structure or composition. The decomposition and nutrient release process of cyanobacteria in the soil mainly occurs in the first 30 days, which can improve the soil nutrient content and enhance bacterial community diversity. The application of cyanobacteria for the remediation of degraded grasslands represents a valuable approach that effectively utilizes cyanobacterial resources.