Study On Response Mechanism Of Plant Functional Traits To Water Level Fluctuation In The Riparian Zone Of The Three Gorges Reservoir (TGR),China

Plant functional traits(PFTs)indicate the response of ecosystem to environmental changes via a single or combined traits matrix.The unique hydrological regulation of the Three Gorges Reservoir(TGR),which is long-term anti-seasonal water level fluctuation,i.e.,water level raise to 175 m elevation in October and then drawdown to 145 m in the coming June.Therefore,a 30-meter hight of riparian zone is established,resulting in significantly change in the ecological environment of the riparian zone ecosystem.The response of PFTs to the TGR hydrological cycle,which affects the vegetation establishment and the ecosystem evolution.In the current study,in order to explore the response and feedback mechanism among hydrological,plant,and ecosystem,we selected the riparian zone in the main stream and tributaries of the TGR as study area,ranging from Wushan county to Fengdu county.Field investigations and analyses on the influence of water level fluctuation to plant communities,PFTs in plant community,PFTs of dominant species were conducted in order to reveal the response of PFTs to water level fluctuation at protein,individual,and community levels.The following results were obtained:(1)The number of plant species in the riparian zone of the TGR is 108.The extinction of species increases significantly compared with that existed in preimpoundment of the reservoir in 2002.The vegetation is dominated by annual and perennial herbs.(2)The dominate plant species varied along the water level gradients in the riparian zone,in which Cynodon dactylon was the dominant species in the lowest water level gradients,Xanthium sibiricum and Cyperus rotundus were dominanted in the middle area of the riparian zone,while X.sibiricum and C.rotundus were the dominant species in the highest area of the riparian zone.The homogenization of plant community is remarkable.The distribution patterns of plant diversity increased and then decreased along with the water level gradients,which is in line with the Intermediate Disturbance Hypothesis(IDH).(3)Along the longitudinal gradients of the TGR,the effect of water level fluctuation to the PFTs in the whole reservoir region showed convergence.However,the significant differences in PFTs along the vertical gradients(water level gradients)were found.In the lowest water level gradient,flooding stress led to the increase on plant traits' convergence.Whereas,in the highest riparian zone,the variations on PFTs were resulted by the combined effects of environmental conditions and plant's inter-and intro-comepetition.(4)Dominant species showed different trade-off strategies in response to the water level fluctuation in the riparian zone.C.dactylon retains a “tolerant” adaptation strategy to adapt the severe flooding disturbance and thus dominates in the lowest water level gradient.X.sibiricum adopts the “quick investment-return” evasive strategy to resist moderate flooding disturbance;and that for C.rotundus is “tolerance” strategy.Therefore,X.sibiricum and C.rotundus become dominant species in the medium water level gradients.(5)The adverse stress of flooding clearly exerts important influences on C.dactylon which are exhibited as molecular,physiological,and morphological variations in leaves at different water-level fluctuation gradients.C.dactylon may contain a rapid antioxidative system to defend flooding stress.Catalase(CAT),as a direct scavenger of hydrogen peroxide,plays an important role in the development of flood tolerance for riparian plants.According to the progress of plant functional traits in the riparian zone and the special concerns on wetland ecology,the following topics should be highly concerned:the biological molecular mechanism on the plant adaptation;the co-evolution mechanism among root functional traits,micro topography and water level fluctuation;the coupling of plant functional traits and biogeochemical process of biogenic elements.