Effects of Soil Chemical Factors on Leaf Traits and Fruit Quality of Litsea mollis Across Altitudinal Gradients

Despite the economic and medicinal value of the tree species Litsea mollis in southern China’s mountain forests, its wild populations remain understudied in terms of their adaptation to altitudinal gradients. This study examined L. mollis populations spanning altitudes of 760–1550 m in Nanshan Park, Hunan Province, to evaluate variation in leaf traits and fruit quality with elevation changes as well as associations with soil chemical properties. Results revealed that increasing altitude corresponded with higher leaf mass, chlorophyll content, soluble compound levels, enzyme activity, and various fruit quality traits (e.g., longitudinal and transverse diameters, weight, and fat, protein, carbohydrate, vitamin A, essential oil, and citral levels). Conversely, leaf area, specific leaf area, petiole length, fruit shape index, fruit stalk length, and ash content declined as altitude rose. Redundancy analysis indicated that specific leaf area, peroxidase activity, and Malondialdehyde content are the primary leaf characteristics influencing fruit quality, and soil pH and total nitrogen, alkaline nitrogen, and available potassium levels were key chemical factors shaping ecological adaptation and fruit quality of L. mollis along the altitudinal gradient. Overall, L. mollis augments light capture and nutrient acquisition by modifying morphological traits, such as leaf area (26.17%) and specific leaf area (44.32%), facilitating adaptation to low-light and nutrient-poor conditions at lower elevations. At higher elevations, plants preferentially allocate resources to increase leaf mass (33.33%) and chlorophyll content (19.02%), improving photosynthetic efficiency, osmotic regulation, and metabolic enzyme activity. This resource allocation promotes nutrient and secondary metabolite accumulation in fruit, enhancing plant stress resistance and fruit quality. This synergistic relationship represents an adaptive adjustment by L. mollis in allocating growth and reproductive resources across different altitude environments. These findings provide a theoretical framework for understanding altitudinal adaptation in L. mollis and offer practical guidance for its introduction, cultivation, and fruit quality improvement in high-elevation regions.