Physiological and Biochemical Ameliorative Effects of Biochar, Trichoderma Harzianum, and Combined Applications in Capsicum Annuum L. Under Water Stress

Abstract

In this study, the ameliorative effect of biochar (B), Trichoderma harzianum (TH) and their combined application (BTH) on plants of Capsicum annuum L. exposed to varying degrees of water deficit was investigated. In control plants exposed to full irrigation (100%) and water restrictions of 75% and 50%, drought stress caused a 20-40% reduction in macro- and micronutrient uptake and a significant increase in oxidative stress indicators (H2O2 and MDA). Under severe water limitation (50%), BTH application increased CAT, POD and SOD activities by more than 40% compared to the control (C50) and reduced H2O2 accumulation by about 25%. However, under moderate or no stress conditions, the SOD activity in the BTH groups was not higher than that of the biochar alone. A significant increase in proline and sucrose accumulation was also observed. At the hormonal level, BTH treatments increased the concentrations of growth-promoting hormones (IAA and GA) by over 1500% and 2900%, respectively, while ABA concentrations decreased by 99.5%. Significant increases of up to 50% were also observed in defense hormones such as SA and jasmonic acid. Principal component analysis (PCA) showed a clear separation of BTH-treated plants from other groups on the basis of growth promotion, antioxidant defense activation, hormonal regulation and osmotic adjustment. Taken together, these results indicate that the combined application of biochar and Trichoderma harzianum significantly improves the physiological and biochemical resistance of Capsicum annuum under water stress conditions and thus represents a promising strategy for sustainable agricultural production.