Residual effects of biochar and nano-modified biochar on growth and physiology under saline environment in two different genotype of Oryza sativa L

Soil salinity is represent a significant environmental stressor that profoundly impairs crop productivity by disrupting plant physiological functions. To mitigate this issue, the combined application of biochar and nanoparticles has emerged as a promising strategy to enhance plant salt tolerance. However, the long-term residual effects of this approach on cereal crops remain unclear. In a controlled pot experiment, rice straw biochar (BC) was applied in an earlier experiment at a rate of 20 t/ha, in conjunction with ZnO and Fe₂O₃ nanoparticles at concentrations of 10 mg L^-1 and 20 mg L^-1. Two rice genotypes, Jing Liang You-534 (salt-sensitive) and Xiang Liang You-900 (salt-tolerant), were utilized under 0% NaCl (S1) and 0.6% NaCl (S2) conditions. Results showed that, application of residual ZnOBC-20 significantly enhanced rice biomass, photosynthetic assimilation, relative chlorophyll content, SPAD index, enzyme activities, K⁺/Na⁺ ratio, hydrogen peroxide (H₂O₂) levels, and overall plant growth. Specifically, ZnOBC-20 increased the tolerance index by 142.8% and 146.1%, reduced H₂O₂ levels by 27.11% and 35.8%, and decreased malondialdehyde (MDA) levels by 33% and 57.9% in V1 and V2, respectively, compared to their respective controls. Residual of ZnOBC-20 mitigated oxidative damage caused by salinity-induced over-accumulation of reactive oxygen species (ROS) by enhancing the activities of antioxidant enzymes (SOD, POD, CAT, and APX) and increasing total soluble protein (TSP) content. Xiang Liang You-900 exhibited a less severe response to salinity compared to Jing Liang You-534. Additionally, residual of ZnOBC-20 significantly enhanced the anatomical architecture of both root and leaf tissues and regulated the expression levels of salt-related genes. Residual of ZnOBC-20 also improved salt tolerance in rice plants by reducing sodium (Na⁺) accumulation and enhancing potassium (K⁺) retention, thereby increasing the K⁺/Na⁺ ratio under saline conditions. The overall results of this experiment demonstrate that, residual effects of ZnOBC-20 not only improved the growth and physiological traits of rice plants under salt stress but also provided insights into the mechanisms behind the innovative combination of biochar and nanoparticles residual impacts for enhancing plant salt tolerance.