Elevation-dependent selection for plasticity in leaf and root traits of Polygonum hydropiper in response to flooding

Selection pressure of flooding promotes the development of phenotypic plasticity of riparian plants; however, whether the selection effects of flooding are elevation-dependent still remains unclear. Seeds of the riparian species Polygonum hydropiper were collected from 10 different locations each at low and high elevations in the Three Gorges Reservoir Region. Plants germinated from these seeds were subjected to control and flooding treatments. Flooding significantly increased both specific leaf area (SLA) and adventitious root biomass but decreased other growth traits of all progeny. In response to flooding, plasticity of all leaf and root traits except SLA varied significantly among seed families (seedlings emerged from the same mother plant) from low elevation. However, among seed families from high elevation, plasticity of only leaf number, total leaf area, and adventitious root biomass varied significantly. For low-elevation seed families, benefits of plasticity in leaf width, leaf number, average leaf area, and leaf biomass were detected across control and flooded conditions. However, in response to flooding, significant costs of plasticity in leaf length, leaf width, average and total leaf areas were found. Therefore, selection effects of flooding impose great pressure on plasticity of leaf and root traits of low-elevation seed families, which is elevation-dependent.