Coupled rhizosphere application of cyanobacteria-bamboo acid hydrolysis extract and cyanobacterial biochar enhances soil health and crop quality

Driven by waste resource utilization and carbon neutrality imperatives, this study synthesized cyanobacterial growth elicitor (CGE) and cyanobacterial-bamboo growth elicitor (CBGE) via acid-hydrothermal hydrolysis. The coupling potential of cyanobacterial biochar (CB) for improving rhizosphere soil and crop quality was investigated through four pot trial treatments: (1) CK (control), (2) BR (rhizospheric CB), (3) LBR (rhizospheric CB with CGE), (4) LZBR (rhizospheric CB with CBGE). Integration of phenotypic analyses, microbiome profiling, functional gene predictions, and risk assessment elucidated biostimulant mechanisms. Compared to CK, all treatments elevated soil nutrient levels. BR exhibited superior nitrogen enrichment (15 ± 3 g/kg), while LBR and LZBR—particularly LZBR—enhanced phosphorus/potassium bioavailability and maximized soil organic carbon (SOC). LZBR treatment markedly increased Chryseobacterium abundance (an organic matter-decomposing genus). Functional verification confirmed enhanced C-N-P cycling activity, minimized environmental nutrient leakage, and improved plant nutrient assimilation. Specifically, LZBR increased soybean grain protein content by 37.0 g/kg and plant nitrogen accumulation by 5.4 g/kg compared to CK, and risk assessments indicated no detectable ecotoxicological effects. Consequently, the coupled application of CGE and CBGE derived from cyanobacteria and bamboo powder simultaneously improves soil quality and crop performance. This approach establishes a novel waste valorization pathway, suitable for partial replacement of chemical fertilizers and carbon emission reduction. CB preferentially adsorbs polysaccharides, dipeptides, and organic acids in CGE and CBGE. LBR and LZBR more effectively boost soil P and K levels with no environmental health risk. CGE and CBGE enhance soil CN P cycling processes. CGE and CBGE significantly improve soybean nutritional quality. CBGE demonstrates superior soil quality amelioration and crop quality enhancement over CGE.