Photosynthetic physio-response of Glyptostrobus pensilis seedlings to mimic soil water changes in the hydro-fluctuation belt of the Three Gorges Reservoir Area

A simulation of soil water changes in the hydro-fluctuation belt of the Three Gorges Reservoir Area was carried out to research the likely photosynthetic eco-physioresponses and corresponding adaptive strategies of Glyptostrobus pensilis seedlings.Four kinds of water treatments were simulated,including normal growth water condition(NG),light drought stress (LD),growth under soil water saturation(SW) and growth with belowground soil submersion(BS).The results showed that different water treatments could significantly influence the parameters of leaf gas exchange and the apparent efficiency of resource use of G.pensilis seedlings.The mean net photosynthetic rate(P_n) of G.pensilis seedlings in LD was 22.025% lower than that in NG over the experimental period.In contrast,the means of P_n in both SW and BS were 18.608% and 48.987% higher than that in NG.Meanwhile,compared with NG,the mean of G_s in LD was significantly lower by 10.218%;whereas the means of G_s in both SW and BS were significantly higher than those in NG by 40.708% and 87.566%,respectively.It demonstrates that G.pensilis seedlings are flood-tolerant and drought-sensitive,with a positive photosynthetic response to sufficient and over-supply of soil water.This is in contrast with a negative photosynthetic response to drought water stress.For the building of a protective forest system in the hydro-fluctuation belt of the Three Gorges Reservoir Area,the species of G.pensilis is suitable for planting in the conditions of root submersion or SW.Root submersion most favors photosynthesis because it()allows P_n to reach its highest point.In cases where G.pensilis is in arid conditions,it should be watered appropriately to maintain its normal P_n.