Effect of Long-time and Deep Submergence on Recovery Growth and Photosynthesis of Three Grass Species in Three Gorges Reservoir Area

Vegetation reconstruction and restoration in the newly formed water-level-fluctuation zone(WLFZ),an anthropogenic-impacted ecosystem,is of great significance in ecological safety in the Three Gorges Reservoir Area of the Yangtze River.Selection of appropriate plant species that are adaptive to long-time and deep submergence is crucial for vegetation reconstruction and restoration in the water-level-fluctuation zone(WLFZ).In this study,a split-plot design was used.Three grass species(Cynodon dactylon,Capillipedium assimile and Paspalum distichum)and four treatments(submerged at depths of 0,5,15 and 25 m)were arranged as the main-plot and sub-plot,respectively.The indices of recovery growth ability and photosynthetic characteristics of each treatment were examined,including photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),water use efficiency(WUE)and apparent CO₂ use efficiency(CUEapp).The important findings were as follows:(1)Cynodon dactylon had the highest survival rate,and its survival rate was 100% in all of the three submerged depths.However,the survival rates of Capillipedium assimile and Paspalum distichum decreased with the increase in submerged depth,and their survival rates were 100% at the submerged depth of 5 m and more than 80% at the submerged depths of 15 m and 25 m.(2)Compared with the unsubmerged control group,each grass specie showed no significant differences in the indices of net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),water use efficiency(WUE)and apparent CO₂ use efficiency(CUEapp)among the three submerged depths.Howerer,Pn,WUE and CUEapp of Cynodon dactylon were much higher than those of Capillipedium assimile and Paspalum distichum when compared with the treatments at the same submergence depth among the three grass species.(3)According to the recovery growth abilities and photosynthesis of three grass species,which were subjected to different stress of submerged depth,they could endure the stress of long-time and deep submergence.Based on the comprehensive consideration on vegetation restoration in the Three Gorges Reservoir Area,the three grass species are suitable for revegetation of water-level-fluctuation zone in the Three Gorges Reservoir Area.The order of endurance of long-time and deep submergence of the three grass species is as the following:Cynodon dactylon >Capillipedium assimile >Paspalum distichum.