Abstract: The soybean(Glycine max) seedlings were treated by Cerium and exposed to ultraviolet-B radiation(UV-B,280-320nm) with hydroponics under laboratory conditions to study the influence of the Cerium(Ⅲ) on root activity,photosynthetic rate(Pn),transpiration rate(Tr) of the soybean seedlings.The results of the static experiments showed that the root activity of the soybean seedlings declined under the 20mg·L-1 CeCl3 treatment induced by UV-B radiation.The Dynamic experimental results showed that the Pn and Tr of the soybean seedlings by 20mg·L-1 CeCl3 treatment increased comparing to the control.The UV-B radiation caused the decline of the Pn and Tr of the soybean seedlings,while the Ce(Ⅲ) plus UV-B treatments eased the decline trend of the Pn and Tr and accelerated their recovery paces.The water use efficiency(WUE) of soybean seedlings increased under UV-B radiation(0.15W·m-2) stress during first four days,and then decreased sharply during the recovery periods from the sixth day to ninth day.The WUE declined obviously under high dose UV-B radiation stress.The range of the WUE by Ce(Ⅲ) plus UV-B treatments was smaller than that by UV-B treatment,while its WUE increased at a faster pace during recovery periods from the seventh day to ninth day.The results of the experiments showed that the Ce(Ⅲ) played an effective role to ease the UV-B radiation stress on the water metabolism of soybean seedlings.

Key words: UV-B radiation, UV-B radiation, Root activity, Transpiration rate(Tr), Photosynthetic rate(Pn), Water use efficiency(WUE)