Light Responses of Nitraria tangutorum to Rain Addition Treatments

Light response curves of a typical desert plant Nitraria tangutorum under four rain addition treatments(+25%,50%,75% and 100% of local mean annual precipitation) were measured with Li-6400xt Portable Photosynthesis Analyzer at the eastern edge of the Ulanbuh Desert,Dengkou,Inner Mongolia.The photosynthesis curves of light intensity were simulated by non-rectangle hyperbolic function and the parameters of photosynthesis were calculated to explore light response characteristics of N.tangutorum to different rain addition treatments.The parameters include the maximum net photosynthetic rate(Amax),apparent quantum yields(AQY),dark respiratory rates(Rd),light compensation points(LCP) and light saturation points(LSP).Under the controlled condition,the Amax,AQY,Rd,LCP and LSP are 13.41 μmol·m-2·s-1,0.029 mol·mol-1,0.61 μmol·m-2·s-1,20.63 μmol·m-2·s-1 and 481.85 μmol·m-2·s-1,respectively.The results show that the net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),the maximum net photosynthetic rate,apparent quantum efficiency and dark respiration rate increased,but the water use efficiency decreased with the rain addition treatments.Therefore,the rain addition changed the physiological characteristics and improved photosynthetic capacity level of N.tangutorum in varying degrees.The results also show that stomatal conductance is the main factor limiting the photosynthetic rate at the stage of light saturation.