Response of leaf functional traits and anatomical structure to altitude in Crataegus songarica K. Koch in Tianshan wild fruit forest

This study investigated the adaptive responses of Crataegus songarica K. Koch to varying altitudes (1 100-1 700 m) in Guozigou, Yili, Xinjiang, China, focusing on leaf functional traits and anatomical structure. Results showed that: (1) An increase in altitude led to a reduction in leaf length, leaf width, leaf area, specific leaf area, and chlorophyll content, but an increase in the leaf length to width ratio, specific leaf weight, and leaf dry matter content, with specific leaf weight showing the strongest plasticity. (2) Higher altitudes were associated with increasing leaf thickness, palisade tissue thickness, and upper and lower epidermis thickness, but decreasing central vein thickness and protrusion, with central vein protrusion showing the strongest plasticity. (3) Leaf area was positively correlated with leaf length, length-width ratio, and specific leaf area, while leaf thickness was positively correlated with upper and lower epidermis thickness and central vein protrusion. Overall, our findings indicated that Crataegus songarica adapts to high-altitude conditions by enhancing leaf thickness and dry matter content for better stress tolerance and by diminishing leaf area and chlorophyll content to mitigate leaf damage from intense sunlight. Conversely, at lower altitudes, the plant increases leaf area and chlorophyll content to facilitate organic matter accumulation.