Abstract: Responses of Potamogeton crispus in turion germination,seedling growth and leaf photosynthesis efficiency were studied in 2 pot culture experiments.The winter experiment had six treatments with controlled light,i.e.2×10⁴-5×10⁴(CK,maximum light intensity at noon),350-450,160-260,60-80,30-50,and 0-30 lx,and lasted 67 days from January 20th to March 28th of 2007.And the summer experiment was carried out in a light incubator,also with six treatments,various in light intensity,that is,1 400,970,660,450,160 and 120 lx,to study light threshold of turion germination under high water temperature in summer was studied.Results show that(1)light intensity had no significant effects on turion germination,which completed on D45 in the winter experiment,while in the summer experiment,light intensity threshold was found to be in the range of 120-160 lx,and over 90% of the turion germinated under the light intensity of 1 400 lx;(2) at the early growth stage,the P.crispus seedlings displayed a higher growth rate(about 1.20 cm·d^-1)in the 5 treatments than in CK(0.92 cm·d^-1),and a reverse trend at the late growth stage,that is,about 1.09 cm·d^-1 in the treatments and 3.15 cm·d^-1 in CK,and moreover,the number of leaves of the seedlings in the treatments did not increase with the growth of P.crispus in plant height;(3)in the winter experiment,beginning on the 39th day after the germination,maximal photochemical efficiency of PSⅡ(F_v /F_m),quantum yield of PSⅡ(ΦPSⅡ)and photochemical quenching(q_p)of the plants declined with decreasing light intensity,and the effect of dim light on PSⅡ of P.crispus was significant,whereas,non-photochemical quenching(q_n)increased,protecting PSⅡ of P.crispus leaves;and(4)long-term exposure to dim light seriously affected the light corresponding capacity of the seedlings.