Abstract: By using CIRAS-2 portable photosynthesis system, the light response processes of Aralia elata photosynthesis and transpiration under different soil moisture conditions were studied, aimed to understand the adaptability of A. elata to different light and soil moisture conditions. The results showed that the response processes of A. elatanet photosynthetic rate (P_n), transpiration rate (T_r), and water use efficiency (WUE) to photon flux density (PFD) were different. With the increasing PFD in the range of 800-1 800 μmol·m^-2·s^-1, P_n changed less,T_r decreased gradually, while WUEincreased obviously. The light saturation point (LSP) and light compensation point (LCP) were about 800 and 30 μmol·m^-2·s^-1, respectively, and less affected by soil water content; while the apparent photosynthetic quantum yield (Ф) and dark respiratory rate (R_d) were more affected by the moisture content. The P_n and WUE had evident threshold responses to the variations of soil water content. When the soil relative water content (RWC) was in the range of 44%-79%, A. elata could have higher levels of P_n and WUE.

Key words: stable isotope, Phragmites australis, feeding habit, Helice tientsinensis, Yellow River Delta, food source