Photosynthesis of Populus euphratica and its response to elevated CO 2 concentration in an arid environment

Abstract

The photosynthetic characterization of Populus euphratica and its response to the elevated carbon dioxide concentration ([CO 2]) were analyzed based on its net photosynthetic rate ( P n), stomatal conductance ( g s), intercellular CO 2 concentration ( C i), transpiration rate ( T r), and water use efficiency (WUE) at different groundwater depths measured by a portable gas exchange system (LI-6400) in the lower reaches of the Tarim River. The results showed that the elevation of [CO 2] decreased the g s, and increased the P n, C i and WUE of P. euphratica. However, the effects of the elevated [CO 2] on g s, P n, C i and WUE varied considerably with groundwater depth. The response of photosynthesis to rising [CO 2] was stronger at the greater groundwater depth (more than 6 m) than that at the shallower groundwater depth (less than 6 m). The critical groundwater depth required to maintain the normal survival of P. euphratica was less than 6 m. When the groundwater depth increased to more than 6 m, P. euphratica encountered moderate water stress, and the plant suffered severe water stress when the groundwater depth increased to more than 7 m.