Dose-Dependent Effects of Paecilomyces variotii Extract on Drought Resistance in Pear Trees: Plant Growth, Soil Enzyme Activities, and Root Exudates

Constrained by site conditions and water resources, pear tree cultivation faces increasing drought stress. Paecilomyces variotii extract (PVE), a novel biostimulant extracted from wild sea buckthorn root-isolated strains and containing chitin, humic/fulvic acids, and beneficial microbes, has gained attention due to its high activity and efficacy in alleviating plant stresses (e.g., drought). In this study, Pyrus pyrifolia &lsquo:Qiu Yue&rsquo: was used as the experimental material, and pot experiments were conducted to examine the drought-mitigating effects of different PVE concentrations. Drought stress was achieved by maintaining soil water content at 35&ndash:45% of water holding capacity for 45 days under natural evaporation conditions in rain shelters. The growth status of pear trees, soil enzyme activity, and metabolite levels were analyzed. The results showed that the application of 5 ng/mL PVE promoted pear tree growth, enhanced leaf antioxidant enzyme activity, and improved photosynthetic capacity and soil enzyme activity. Under normal water conditions, the shoot growth length, plant height, stem diameter, and root system activity of the 5 ng/mL PVE group were 31.91%, 12.05%, 3.54%, and 10.94% higher than those of the control group, respectively. Under drought stress, these values increased by 25.12%, 8.87%, 12.21%, and 16.98%, respectively. The addition of 5 ng/mL PVE facilitates trehalose release and upregulates starch-sucrose, glycerophospholipid, and galactose metabolic pathways, thereby potentiating drought stress tolerance in pear trees. However, at 20 ng/mL, reductions were observed in pear tree growth indicators, leaf antioxidant enzyme activity, soil enzyme activity, and trehalose content in root exudates compared to the 5 ng/mL PVE treatment. Overall, 5 ng/mL PVE effectively promotes pear tree growth and enhances drought resistance, making it suitable for broader use in pear cultivation practices.