Microbial-inoculated biochar combined with nitrogen mitigates salinity stress in rice by reducing salt accumulation and enhancing soil–plant interactions

Microbial-inoculated biochar and N can enhance plant productivity under saline conditions through improving the chemical and biological properties of soil and the plants’ self-defense system. A pot experiment with 11 treatments was conducted to evaluate the effectiveness of rice husk biochar, with and without microbial (bacterial and fungal) inoculation, combined with nitrogen (N) in mitigating salinity stress (6.8 ds/m EC) in rice. Treatments included sole nitrogen (60 and 120 kg ha - ¹), sole biochar (1%), microbial-inoculated biochar (fungal or bacterial), and their combinations with nitrogen at 60 and 120 kg ha - ¹, applied under both saline and non-saline conditions. Two rice varieties were used: the salt-tolerant Shuang Liang You 138 (SLY138) and the salt-sensitive Jing Liang You 534 (JLY534). The experiment was conducted for 80 days. The combined application of bacterial-inoculated biochar (BB) and nitrogen fertilizer was more effective than rice husk biochar alone in improving soil microbial and chemical properties. Notably, bacterial-inoculated biochar combined with nitrogen 120 kg ha ─1 (BB + N) treatments increased the abundance of pollution-degrading Desulfobacterota and salt-tolerant Actinobacterota. The enrichment of these microbial groups was associated with prolonged incubation time and reduced soil Na + concentrations, which collectively contributed to improved rice growth. Compared to BC treatment, BB + N120 treatment produced higher proline, total soluble sugar (TSS), leaf water potential (Ψw), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in SLY138 by 120%, 167%, 30.23%, 50%, 68%, and 57%, respectively, under saline conditions and NH 4 + –N, OM, and bacterial and fungal community richness by 113.33%, 40%, 65.33%, and 186.25%, respectively. The salt tolerance of SLY138 may be correlated with the enhanced activities of SOD, POD, and CAT and more accumulation of proline and total soluble sugar. The findings of our study demonstrate the effectiveness of modified biochar applications in mitigating salinity stress and enhancing rice growth in saline environments.