Variations In Eco-physiological Adaptability Of Populations Of Polygonum Hydropiper To Flooding In The Hydro-fluctuation Belt Of The Three Gorges Reservoir

Riparian species often tend to exhibit certain trait plasticity in response to O2 deficiency and low light under flooding conditions.Previous studies have shown that flooding stress could lead to intraspecific genetic differentiation and formation of different genotypes.Trait plasticity of different genotypes may be different in response to flooding.The plasticity can be costly if it decreases plant fitness;while it will be beneficial if the plasticity improves plant performance.Therefore,trait plasticity may play an important role in evolutionary process of plants.The plants of a same species distributed at the low and the high elevations of the hydro-fluctuation belt of the Three Gorges Reservoir may undergo genetic differentiation and develop different trait plasticity due to the long-term experience of different flooding regimes.However,whether the trait plasticity has certain evolutionary potential or not remains to be further investigated.An annual herb,Polygonum hydropiper L.,was chosen for this study.It is naturally distributed at the low and the high elevations of the hydro-fluctuation belt of the Three Gorges Reservoir.By conducting a field experiment,implementing a common garden experiment and applying multiple plasticity models,growth and physiological characteristics of P.hydropiper distributed at the low-and the high-elevation populations in the field were analyzed;variations in seed germination,growth and physiological characteristics of populations of P.hydropiper originated from the low and the high elevations were compared;variations in growth and physiological characteristics of different genotypes of P.hydropiper were analyzed and costs and benefits of plasticity in morphological and physiological traits of different genotypes of P.hydropiper in response to flooding were analyzed.The main results are as follows:(1)Significant differences were found in growth,morphological and physiological traits of P.hydropiper of the low-and the high-elevation populations.Compared with plants from low elevation,plants from high elevation had significantly higher biomass and thicker leaves,but lower allocation to reproduction and lower germination rate;(2)Maternal effect significantly improves the performance of the offspring in response to flooding.Genotypes originated from low-elevation populations had higher specific leaf area and variation in leaf traits than those from high-elevation populations;(3)The costs and benefits of leaf trait plasticity of genotypes originated from the low and the high elevations were significantly different.Genotypes from the low elevation exhibited higher values of leaf number,leaf area and leaf width across control and flooding environments,showing significant benefits;however,these genotypes increase the values of leaf area,leaf length and leaf width,exerting significant costs to overall fitness under flooding environment.Significant differences in leaf traits of P.hydropiper between the low-and high-elevation populations distributed at the hydro-fluctuation belt of the Three Gorges Reservoir,which suggests that genetic differentiation may occur in these populations.The responses of leaf traits of genotypes originated from the low elevation are more active to flooding,which may increase the fitness of the low-elevation population at the hydro-fluctuation belt,showing certain evolutionary potential and could be applied to vegetation restoration in hydro-fluctuation belt.This study could further improve researches on the adaptive evolution of riparian plants to environmental stress,and provide theoretical and scientific evidence for vegetation restoration and reconstruction in the degraded hydro-fluctuation belt of reservoirs or riparian region.