Effects of waterlogging and increased soil nutrients on growth and reproduction of Polygonum hydropiper in the hydro-fluctuation belt of the Three Gorges Reservoir Region

Aims Flooding and soil nutrients are the main environmental factors that affect plant growth in the hydro-fluctuation belt of the Three Gorges Reservoir Region (TGRR). Flooding intensity and concentration of soil nutrients experienced by riparian plants at different elevations of the hydro-fluctuation belt are different; therefore, we hypothesized that growth and reproductive responses of plants of the same species from different elevations to waterlogging and increased soil nutrients are also different.Methods In this study, the riparian species Polygonum hydropiper, which is widely distributed at low and high elevations of the hydro-fluctuation belt of the TGRR, was selected and its seeds were collected from natural populations. Effects of waterlogging and soil nutrients on growth and reproductive traits of P. hydropiper from high- and low-elevation areas were studied in a common-garden greenhouse experiment.Important findings Waterlogging significantly, or with marginal significance, decreased length and width of functional leaves, total branch number, leaf biomass, flower biomass, and total biomass of plants; low nutrient treatment significantly or marginal significantly decreased total node number, total branch number, root biomass, flower biomass, and total biomass of plants, indicating that both waterlogging and low soil nutrients inhibited growth and reproduction of P. hydropiper. Moreover, the interaction between waterlogging and soil nutrients significantly affected root biomass, showing higher root biomass accumulation at high soil nutrient conditions upon waterlogging. The high-elevation plants had significantly or marginal significantly higher leaf and root biomass than those from low elevation; however, flowering time of the low-elevation plants was significantly earlier, and reproduction allocation was higher than the high-elevation plants, indicating that resource allocation strategy was different between the high- and the low-elevation plants. The results indicate that growth and reproduction of P. hydropiper are inhibited by both waterlogging and soil nutrients, and this species has high adaptability at high soil nutrient conditions to waterlogging; meanwhile, low-elevation plants can adjust their growth and reproductive characteristics to improve their fitness under environmental stress.