Photosynthetic Responses of Two Woody Halophyte Species to Saline Groundwater Irrigation in the Taklimakan Desert

Abstract

The study of plant photosynthesis under different degrees of drought stress can provide a deeper understanding of the mechanism of plant drought resistance. In the Taklimakan Desert, saline groundwater is the only local water source with regard to shelterbelt construction and determines plant growth and photosynthetic changes. In this study, daily dynamics of gas exchange parameters and their responses to photosynthetic photon flux density at three irrigation levels (W1 = 17.5, W2 = 25, W3 = 35 mm) were measured for two main species, i.e., Calligonum mongolicum (C) and Haloxylon ammodendron (H). H was better adapted to drought stress than C. Net photosynthetic rate (PN) was mainly related to soil water status in the main root system activity layer. In July, the daily variations of PN and transpiration (Tr) for C were higher than H. C increased water use efficiency (WUE) with increases in PN, while H decreased Tr to obtain a higher WUE. Either C or H, drought reduced the low light and metabolic capacity, and thus decreased the light adaptability and photosynthesis potential. We suggest a prerequisite understanding of physiological mechanisms and possible plant morphological adjustments required to adapt plant species to desert drought conditions.