Biochar (BC), a charred organic material produced through pyrolysis, has emerged as a promising and an environmentally friendly agro-strategy. This study investigated its potential to mitigate the impacts of global climate change on maize cultivation, specifically focusing on temperature stress tolerance. The research examined how the source material of biochar influences key plant stress mechanisms, including antioxidant enzymes and heat shock proteins (HSPs). To achieve this objective, the study evaluated the effects of biochar derived from three distinct sources-apple orchard pruning waste (PWBC), urban waste (UWBC), and animal manure (AMBC)-on maize plants grown under controlled conditions. A completely randomized factorial design with three replications was employed. Each biochar type was applied at a rate of 4% (w/w) to the soil. The physiological responses of maize plants were assessed under normal (25 degrees C), low (4 degrees C), and high (48 degrees C) temperature conditions. Lipid peroxidation (indicator of oxidative stress), soluble protein content, activity of antioxidant enzymes, and expression levels of HSP70 and HSP90 were analyzed. The results revealed that PWBC application, compared to without BC, significantly reduced malondialdehyde (MDA) accumulation by 38% under both low- and high-temperature stress, suggesting its potential in alleviating oxidative damage. UWBC treatment, on the other hand, demonstrated a pronounced effect on protein metabolism, with soluble protein content increasing by 16% at low and 26% at high temperature. Furthermore, biochar application under temperature stress increased antioxidant enzyme activity, thereby mitigating oxidative stress, with UWBC proving to be the most effective in stimulating antioxidant responses. The expression levels of HSP70 and HSP90 were also significantly regulated by biochar application. UWBC and AMBC treatments displayed the most pronounced effects, with HSP70 expression increasing by 4.6- and 1.6-fold, and HSP90 expression by 8.2- and 45.4-fold, respectively, particularly under high-temperature stress, compared to without BC. These findings indicate that the reduction of lipid peroxidation, activation of antioxidant defense mechanisms, and regulation of HSP70 and HSP90 transcriptional and translational in maize plants under temperature stress vary based on the source material of the biochar. Long-term studies assessing plant yield and quality are recommended to validate these findings further.

The impact of biochar application on plant performance under drought stress necessitates a comprehensive understanding of biochar-soil interaction, root growth, and plant physiological processes. Therefore, pot experiments were conducted to assess the effects of biochar on plant responses to drought stress at the seedling stage. Two contrasting maize genotypes (drought-sensitive KN5585 vs. -tolerant Mo17) were subjected to biochar application under drought stress conditions. The results indicated that biochar application decreased soil exchangeable Na+ and Ca2+ contents while increased soil exchangeable K+ content (2.7-fold) and electrical conductivity (4.0-fold), resulting in an elevated leaf sap K+ concentration in both maize genotypes. The elevated K+ concentration with biochar application increased root apoplastic pH in the drought-sensitive KN5585, but not in the drought-tolerant Mo17, which stimulated the activation of H+-ATPase and H+ efflux in KN5585 roots. Apoplast alkalinization of the drought-sensitive KN5585 resulting from biochar application further inhibited root growth by 30.7%, contributing to an improvement in water potential, a reduction in levels of O2-, H2O2, T-AOC, SOD, and POD, as well as the down-regulation of genes associated with drought resistance in KN5585 roots. In contrast, biochar application increased leaf sap osmolality and provided osmotic protection for the drought-tolerant Mo17, which was associated with trehalose accumulation in Mo17 roots. Biochar application improved sucrose utilization and circadian rhythm of Mo17 roots, and increased fresh weight under drought stress. This study suggests that biochar application has the potential to enhance plant drought tolerance, which is achieved through the inhibition of root growth in sensitive plants and the enhancement of osmotic protection in tolerant plants, respectively. Biochar application decreased soil exchangeable Na+ and Ca2+, but increased soil exchangeable K+ and electrical conductivity.Biochar increased apoplastic pH, but reduced root growth, stress damage and stress response during drought for the drought-sensitive KN5585.Biochar improved osmotic protection, trehalose accumulation, and fresh weight during drought for the drought-tolerant Mo17.