干旱区胡杨光合作用对高温和CO_2浓度的响应

Photosynthesis of Populus Euphratica olive and its response to CO_2 concentration and high temperature in arid environment

采用LI-6400便携式光合作用测定仪实测的塔里木河下游胡杨(Populus euphratica oliv)光合作用参数,探讨了不同地下水埋深下的胡杨光合作用对CO2浓度增加和温度升高的响应。结果表明:(1)CO2浓度升高减小了胡杨气孔导度,促进了光合速率、胞间CO2浓度和水分利用效率的增加,但不同地下水埋深下,胡杨光合作用参数对CO2浓度升高的响应不同,干旱环境(地下水埋深较深)下的响应程度大于水分适宜(地下水埋深浅)环境下的响应;(2)高温引起胡杨气孔发生不完全关闭,导致了光合作用的光抑制发生,从而降低了胡杨光合速率,但降低程度受水分条件的影响,地下水埋深较深环境下的影响程度大于地下水埋深浅的;(3)地下水埋深是控制干旱区胡杨光合作用对CO2浓度和温度升高的根本因素,6m是胡杨生长正常的临界地下水埋深,地下水埋深>6m,胡杨即遭到水分胁迫,地下水埋深>7m,胡杨即受到了较严重的水分胁迫。

Based on data of net photosynthetic rate （Pn）, stomatal conductance （gs）, intercellular CO2 concentration （Ci）, transpiration rate （Tr）, water use efficiency （WUE） measured by a portable gas exchange system （LI-6400） in Populus euphratica olive grown at different groundwater depths in the lower reaches of the Tarim River, the photosynthetic characterization of P. euphratica and its response to the elevated CO2 concentration, ／[CO2／], and temperature were analyzed. Results showed that the elevation of ／[CO2／] decreased gs, increased Pn, Ci, WUE in P. euphratica, but the magnitude of the effect of elevated ／[CO2／] on gs, Pn, Ci, WUE varied considerably with groundwater depth; the response of photosynthesis to rising ／[CO2／] was stronger at the deeper groundwater depth than at the shallower groundwater depth. High temperature led to non-uniform stomatal closure and photoinhibition, which ultimately decreased the photosynthesis of P. euphratica. The magnitude of decrease resulting from higher temperature was stronger at the deeper （〉6m） than at the shallower groundwater depth.（〈6m）. Our study indicates that groundwater depth is the critical factor controlling the response of photosynthesis of P. euphratica to elevated ／[CO2／] and temperature, and that 6m is the threshold groundwater depth for the normal growth of P. euphratica. When the groundwater depth increased to more than 6m, P. euphratica would encounter moderate water stress, and subject to severe water stress when the groundwater depth is at 〉7m.