不同林龄梭梭（ Haloxylon ammodendron ）的光合特性和水分利用效率

It is important to understand the variation of photosynthetic characteristics and water use efficiency （WUE） response to light， and the differences that existed in different growing years of Haloxylon ammodendron. It helps to reveal the differences in physiological characteristics of H. ammodendron at the different growth stages， and the knowledge of environmental adaptation strategies， which is important for ecological restoration in extreme arid areas. In this study， we measured the light response curves of H. ammodendron of different growing years respectively， 5 a， 11 a， 22 a， 34 a and 46 a. The photosynthetic characteristics and water use efficiency were compared and analyzed among them. The results showed that： （1） With the increasing of photosynthetic radiation （I）， the variation trends of the net assimilation rate （Pn） and transpiration rate （Tr） were similar in different growing years of H. ammodendron. The photosynthetic capacity of H. ammodendron planted in recent years（5 a， 11 a） was stronger， while the photosynthetic characteristics of H. ammodendron planted in the early years（34 a， 46 a） tended to be stable； with the increasing of planting years， the photosynthetic capacity of H. ammodendron had a decreasing trend. （2） WUE of different planting years of H. ammodendron showed a non-linear increase with the increasing of I. For H. ammodendron， WUE of 22 years was higher than that of lower ages （5 a， 11 a） and higher ages （34 a， 46 a）. And the middle-aged H. ammodendron （22 a） was subjected to the greatest water stress and improved water use efficiency by reducing transpiration， while higher-aged H. ammodendron （34 a， 46 a） showed significant degradation. This reflects that H. ammodendron has developed its own extreme drought resistance mechanism and water regulation strategy under extreme drought conditions.

Keywords： light response curve model ; photosynthetic characteristics ; water use efficiency ; Haloxylon ammodendron