Abstract:

Abstract： Saussuea involucrata is a rare and endangered alpine species， and it is widely used utilization in traditional Chinese medicine. It naturally distributes in the elevation range of 2 400～4 000 m in the Tianshan Mountains of northwest China. Its adaptability to the natural environmental conditions is the basis for its conservation and reproduction，but this aspect has rarely been studied. In this paper，we selected typical plants of S. involucrata in three elevation (the low，middle and high) zones of its natural distribution，measured and compared the photosynthetic and relevant ecophysiological characteristics. Through analysis of these characteristics，we can further understand the adaptability to its natural environment，and lay scientific basis for the conservation and sustainable utilization for this rare and endangered species. We divided the natural distribution habitats of S. involucrate into three zones，i.e. the low elevation zone (2 600～2 650 m)，the middle elevation zone (2 651～2 850 m)，and the high elevation zone (≥2 851 m). The photosynthetic and relevant ecophysiological characteristics for each one leaf from each of the five plants of S. involucrate were selected in each zone. The photosynthetic and related ecophysiological characteristics of S. involucrata were measured by Portable LI6400 Photosynthesis System from 2 August to 8 August，2006. The results showed that light compensation point（LCP） of S. involucrate in the three zones was (1569±031)μmol·m^-2s^-1，(1594±005)μmol·m^-2s^-1，and (19.93±0.12)μmol·m^-2s^-1，respectively. Light saturation point (LSP) of them were 1 550～1 610 μmol·m^-2s^-1，without significantly difference among the three elevation. There was no significant difference in apparent quantum requirement (AQY) of S. involucrate among the three zones，while significant difference existed among the maximum net photosynthetic rate (P_max) among the three. However, carboxylation efficiency (CE) of S. involucrate in high elevation zone was significantly different with those in the lower middle elevation zones respectively. In the same site，photosynthetic respiration rate （R_p） of S. involucrate was higher than dark respiration rate (R_d). From 8： 00 O'clock to 20： 00 O'clock，the diurnal changes of P_n，T_r，and G_s were single peak in the low elevation zone. When S. involucrate did not receive direct sunlight radiation，P_n decreased quickly，Tr decreased slowly while G_s increased. This showed that stomatal characteristics of S. involucrate had strong sensitivity to light. From low or high elevation mean value of P_n in a day decreased with elevation，while PE increased with elevation. But the changes of WUE and L_s had no significant relationship with elevation. Pn of S. involucrate was significant and positively correlated with T _l，T_a，and PAR，negatively correlated with E，and had no significant correlation with RH and C _a. The Tr of S. involucrate significantly and positively correlated with T_l，T_a，and PAR，negatively correlated with RH. The Gs of S. involucrate negatively correlated with C_a. The P_n of S. involucrate significantly and positively correlated with Tr，G_s and V_pdl，negatively correlated with C_i.

Key words: Key words： Saussuea involucrata, net photosynthetic rate, transpiration, stomatal conductance, Tianshan Mountains