LAUSR

Vallisneria natans is often used for the ecological restoration of aquatic vegetation. V. natans thalli were cultured under ambient (400 ppm) and increased carbon supply, with low (18 °C) and high temperature (25 °C). The thalli were used to examine the effects of increased carbon and high temperature on the growth, nitrogen metabolism and photosynthetic characteristics of this plant. At 18 °C, the relative growth rate (RGR), N uptake rate and nitrate reductase (NR) activity of V. natans thalli grown under ambient carbon supply were lower than those under increased carbon supply. The increased carbon supply decreased the RGR, N uptake rate, NR activity and maximum inorganic carbon (Ci) -saturated photosynthetic rate (Vmax) of V. natans when it was cultured at 25 °C. Regardless of the carbon supply levels, the growth, nitrogen uptake capacity and photosynthesis of V. natans thalli grown at 25 °C decreased compared with those of V. natans thalli grown at 18 °C. The RGR and photosynthetic rate of V. natans grown in the presence of increased carbon supply and high temperature were the lowest amongst the four different conditions. Therefore, the negative effects caused by a high temperature were pronounced under the condition of a global atmospheric CO2 increase.