Abstract:In order to explore the adaptation mechanism of Cyperus rotundus seedlings to the water level change in the hydro-fluctuation belt of the Three Gorges Reservoir area,we conducted a simulation experiment to study the physiology response to different submerged environments induced by the water level change.Four treatments were set,i.e.,no submergence(CK),root submergence(T1),semi-plant-submergence(T2),and whole plant submergence(T3).The results indicated that:(1)After treated for 45 days,chlorophyll a,chlorophyll b,carotenoid and total chlorophyll in all submergence treatments tended to be decreased,while chlorophyll a/b still kept the CK level.(2)Submergence had no significant effects on the contents of soluble protein,proline and soluble sugar in T1 and T3,but it significantly increased the contents of proline and soluble sugar in T2.(3)With the increase of submergence time,the content of MDA was gradually increased in all submergence treatments,and was significantly different compared with CK after 15-day submergence.(4)The activities of antioxidant enzyme(such as SOD,CAT and APX)in all submergence treatments had some increase during the submergence,however,the activities of SOD and CAT in T3 were gradually reduced as the submergence continue to increase.(5)After treated for 45 days,the starch concentrations in leaves and roots in all submergence treatments were higher than that in CK.This study indicates that although submergence have some adverse effects,C. rotundus can increase the physical defense to the submergence by adjusting a variety of inner protective enzyme activities and the contents of osmotic adjustment substances.Meanwhile,the accumulation of large amount of starch in root can offer a stable energy supply for tolerance to submergence.