Abstract:To research the impacts of soil water alternative variation on photosynthetic characteristics of Pinus elliottii seedlings,four different kinds of water treatment simulating processes in the Three Gorges Reservoir Area from flooding to drought were applied,including regular water supply (CK),regular water supply-mild drought-rehydration (DR),flooding (FL),flooding-mild drought-rehydration (FD).Results showed that:(1)Water treatment could significantly influence net photosynthetic rate,stomatal conductance,transpiration rate,intercellular carbon dioxide concentration,water use efficiency and photosynthetic pigment content of P.elliottii seedlings (P<0.05).(2)In the earlier and middle stage of experimental period,photosynthetic rate,stomatal conductance and transpiration rate showed significant decline in DR,FL and FD compared with CK,whereas those in DR and FD came back to a high level later.(3)Every treatment showed increase in water use efficiency with contrast to CK to different extents in the whole experimental period,with the maximum of 4.95 μmol·mmol-1 in DR.(4)Along with the extended period of time,an increase followed by decline tendency was displayed in contents of total chlorophyll,chlorophyll/carotenoid and chlorophyll a/b in four treatments.Chlorophyll/carotenoid ranged from 4.379 to 6.019 while that of chlorophyll a/b was 2.207 to 2.850.These results indicated that P.elliottii seedling has a competitive adaptation to flooding and “flooding-drought” alternative variation in terms of growth,water metabolism and photosynthetic physiology.Additionally,it could recover growth condition rapidly after stress release.Therefore,P.elliottii could be a candidate species for revegetation of riparian in the Three Gorges Reservoir Area.