Abstract: To understand the physiological adaptability of Excentrodendron hsienmu to arid habitat of karst mountains, a moisture control experiment was conducted with 2-year-old E. hsienmu seedlings in a water supply device, which was set up with a simulated karst structure comprising soil, limestone, and epikarst layer. A twofactor design, soil layer and epikarst layer water gradient condition, was performed to examine leaf photosynthetic and resistance physiological characteristics of E. hsienmu seedlings. The results showed that the photosynthesislight response curve of the seedlings well fitted the nonrectangular hyperbola model. Light response curve under different treatments in epikarst layer showed the similar variation. Results of twoway analysis of variance showed soil layer water significantly affected the maximum net photosynthetic rate (P_max) and dark respiration rate. Both factors and their interaction had markedly significant effects on relative chlorophyll value. The P_max and dark respiration rate decreased, while relative chlorophyll value increased with the increases of soil drought stress. Soil layer water very significantly affected free proline, and had significant impact on both malondialdehyde content (MDA) and peroxidase (POD) activity. Content of free proline in drought stress groups was significantly higher than that in control, while MDA content under severe drought stress was significantly higher than that in control. Peroxidase activity increased firstly, and then decreased with the increases of soil drought stress, with the peak occurring in moderate drought stress. Our results demonstrate that E. hsienmu has strong tolerance to drought stress, with the active adaptation of osmotic adjustment as the main reason.

Key words: fire disturbance, leaf functional trait, Larix gmelinii community, species diversity, functional diversity