Short-Term Physiological Responses of Black Locust Saplings to Trichoderma-Based Root Priming Under Field Drought Conditions

Black locust (Robinia pseudoacacia L.) has exceptional growth capacity in nutrient-poor environments and is therefore widely used for afforestation and land reclamation on degraded soils. However, drought stress can restrict sapling growth, which undermines the success of their establishment. The effect of a product containing two endophytic strains (Trichoderma afroharzianum P. Chaverri, F.B. Rocha, Degenkolb & Druzhinina TR04 and Trichoderma simmonsii P. Chaverri, F.B. Rocha, Degenkolb & Druzhinina TR05) was studied on a black locust sapling stand under severe drought in eastern Hungary. The two-year-old saplings were root-soaked before planting in sandy soil. The growth of Trichoderma-treated plants improved by late spring. Compared to the control trees, average height increased by 25.75%, and root collar diameter was 21.96% larger. Treated plants also showed 9.1% higher chlorophyll content and 11.1% Normalized Difference Vegetation Index (NDVI). The reduced intercellular CO2 concentration, together with slightly lower stomatal conductance and increased transpiration rate, suggests tighter stomatal regulation and altered water-use dynamics under drought conditions. These responses indicate improved short-term drought acclimation rather than enhanced carbon assimilation capacity. Pre-planting inoculation with endophytic Trichoderma strains provides a sustainable method to enhance the early establishment and drought resilience of black locust, thereby increasing the efficacy of forest restoration by improving the survival of black locust on challenging degraded sites.