Search

The Three Gorges Dam has created a new riparian zone which is called 30m-water-level fluctuating zone of the Three Gorges Reservoir of the Yangtze River.Altered ecosystems of the riparian zone can disrupt the hydrological regime by reducing inundation,or creating longer term submergence,which adversely affects riparian vegetation,and in particular,the native plant species.Chinese wingnut(Pterocarya stenoptera) is a dominant native riparian tree species in the Three Gorges Reservoir region,and thus has to face the modified riparian environment.In order to shed light on the impacts of soil water regimes in this region on the Chinese wingnut,4 water treatments were imposed on 1-year-old seedlings of Chinese wingnut for more than 2 months.The water treatments included normal water supply(CK),normal water supply-light drought-normal water supply(DR),flooding(FL) and flooding-light drought-normal water supply(FD),which simulated the modified hydrological regime in the riparian zone of the Three Gorges Reservoir region.The treatment of 3 stages for DR and FD groups lasted 33,30 and 15 days respectively.The effects of water treatments on photosynthetic parameters,photosynthetic pigment contents and chlorophyll fluorescence characteristics of Chinese wingnut seedlings were investigated after 0,33,63 and 78 days of water treatment.The results showed that net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),photosynthetic pigment contents(chlorophyll a,chlorophyll b and carotenoid) and water use efficiency(WUE) of Chinese wingnut seedlings were reduced significantly in DR,FL and FD treatments as compared to CK.However,the chlorophyll fluorescence features of Chinese Wingnut seedlings in these three treatments were slightly reduced comparable to that of CK.Compared to other three treatments,seedlings in FL group were adversely influenced dramatically.At the end of the treatment,the Pn of Chinese wingnut seedlings under FL treatment was reduced by 65.9%,WUE was reduced by 65.7%,and total chlorophyll content was reduced by 68.7% comparing with that of CK.In contrast to CK group,Pn,Tr,Gs and total chlorophyll in FD groups were also decreased significantly in the beginning of the treatment due to flooding and drought,but they were increased significantly after rehydration.The seedlings in DR groups showed similar but lower variation as to those of FD.The results suggested that the seedlings of Chinese wingnut were sensitive to soil water stress including flooding and drought,although they showed obvious tolerant ability to water stress in terms of the characteristics of morphology,photosynthesis,water use efficiency and chlorophyll fluorescence.Additionally,all of them showed excellent recovery ability after stress being released.Therefore,Chinese wingnut might be suitable to the modified hydrological regime caused by the Three Gorges Dam,and thus could be applied to vegetation reconstruction in the water-level fluctuating zone of the Three Gorges Reservoir for its adaption to drought,flooding and "flooding-drought" alternative variation.