Abstract:

The eco_physiological responses of dominant trees (Atraphaxis frutescens andElaeagnus angustifolia) to ground water availability were investigated in a controlled environment at the Plant Transpiration Consume Water Observation Station in Minqin Desert Botanical Garden, Gansu province. In this experiment, the depths of groundwater (DGW) were designed as 1.4 m, 2.4 m and 3.4 m. In each treatment, the two desert species were transplanted to the observation sites with different DGW after growing naturally for 3 or 4 years. The results showed that: 1) the changes of DGW resulted in the significant changes of net photosynthetic rate (Pn), the transpiration rate (E), stomatal conductance (Gs), leaf contents of chlorophyll a (Chl a), chlorophyll b (Chl b) and the total chlorophyll (Chl a + Chl b), the ratio of Chl a and Chl b (Chl a/Chl b), the quantum yield efficiency and the CO2 carboxylation efficiency; 2) although these two desert species were well adapted to the water stress environment at 3.4 m DGW, their adaptive strategies were different. In response to the water stress environment, A. frutescens  reduced its photosynthetic rate and maintained the level of water use efficiency, while E. angustifolia largely decreased the transpiration rate and thus increased the water use efficiency; 3) in different DGW, the optimal temperature of photosynthesis in these two desert species did not change significantly, but the net photosynthetic rate under the optimal temperature range declined markedly. Since E. angustifolia  is a nitrogen fixation species, further studies are needed to verify whether or not the differences of drought adaptation between these two species are related to the nitrogen fixation.