Carbon to nano-carbon: comparative efficacy of conventional biochar and SiO2-nanoparticles inoculated biochar in enhancing physiological, anatomical, and molecular salt tolerance in rice

Soil salinity severely limits rice productivity by impairing photosynthesis, disturbing ion homeostasis and accelerating oxidative injury. The study aimed to evaluate the comparative efficacy of biochar (BC), SiO 2 nanoparticles (Si-NPs) and their combined composite SiO 2 nano-modified biochar (SBC) in enhancing salt tolerance in rice. Material characterization (SEM, TEM, FTIR, XRD) confirmed successful anchoring of SiO 2 onto the biochar matrix, forming a highly reactive nano-carbon composite. In this study rice plants under moderate salinity (EC ≈ 7 dS m -1 ) conditions exhibited pronounced growth inhibition, excessive Na + accumulation, elevated oxidative damage and impaired photosynthetic performance. In contrast, application of SBC substantially outperformed BC and Si-NPs and markedly alleviated stress symptoms. Relative to the CK-S, SBC reduced H 2 O 2 and MDA by 55.4% and 38.2%, respectively, and enhanced SOD, POD and CAT activities by 39.5, 47.3% and 31.3%. Photosynthetic performance also improved significantly, with increase of 72.5% in Pn , 77.2% in Gs , 178.6% and in ETR . SBC also improved the osmotic adjustment raising starch and sucrose content by 62.1% and 70.9% while reducing excessive proline accumulation by 30.6%. Ion homeostasis improved through lower Na + uptake and higher K + retention resulting in a markedly higher K + /Na + ratio through application of SBC. Furthermore, SEM imaging and transcript analysis revealed improved stomatal structure and root anatomical resilience while qRT-PCR showed upregulation of key stress-responsive genes associated with antioxidant and ion-transport pathways. These findings demonstrate that SBC provides a synergistic biochar-nanoparticle mechanism that comprehensively enhances rice tolerance to salinity, offering a promising and sustainable amendment for improving productivity in salt-affected agricultural systems. • Salinity stress severely induces Na + toxicity, ionic imbalance, and physiological dysfunction in rice plants. • SiO 2 -inoculated biochar (SBC) offers a scalable amendment to mitigate Na + toxicity in saline agricultural soils. • SBC enhances K + uptake, antioxidant activation, and coordinated regulation of ion-transport and stress-responsive genes. • SBC improves PSII function, carbohydrate metabolism, and root–stomatal anatomy, enhancing rice performance in salt-affected fields