Effects of altitude on water and carbon metabolism and growth of hippophae rhamnoides in Guandi Mountain

Altitude is an important environmental factor that affects Chinese seabuckthorn（Hippophae rhamnoides L. subsp. sinensis Rousi） distribution and growth. The balance of water metabolism and carbon metabolism is the basis of plant survival and growth. Studies about the effect of altitude on water-carbon metabolism and growth of Chinese seabuckthorn will contribute to fully understanding its adaptability and physiological mechanism to altitude. In this study, wild Chinese seabuckthorn growing in Guandi Mountain area of western Shanxi Province was used as the study object. Twig water potential, branch percentage loss of conductivity（PLC）, photosynthesis and nonstructural carbohydrate（NSC） concentration of female seabuckthorn plants at elevation1100 m to 2100 m were measured in June and August, and plant height and crown width were also measured at different elevations. The results showed that with the elevation increasing, the soil water content increased in both June and August, and the midday twig water potential increased first and then decreased. The branch PLC decreased first and then increased in June.With the increase of altitude, the branch vessel diameter did not change significantly, but the vessel density, branch maximum specific water conductivity and leaf area increased first and then decreased. And the net photosynthetic rate increased in June and August. There was no significant change of NSC content in both roots and leaves. With the increase of altitude, both tree height and crown width increased first and then decreased. The above results suggested that the growth of seabuckthorn was inhibited to some extent at both low altitude（1100-1300 m） and high altitude（1900-2100 m）. Seabuckthorn at low altitude was mainly affected by drought stress. And the growth inhibition at high altitude was reflected in the poor water status resulting from low temperature, shortened growing season and the inhibition of low temperature on tree growth.