Competition between Chara aspera and Potamogeton pectinatus as a function of temperature and light

Abstract

Two experiments were carried out to study the interaction between Chara aspera Deth. ex Willd. and Potamogeton pectinatus L. The purpose of the first experiment was to assess the effect of temperature on the rate of emergence and the second was designed to study the effect of light on the competition during the established phase. P. pectinatus tubers sprouted after about 4 days at 16°C and 9 days at 10°C, which was sooner than either oospores or bulbils of C. aspera (about 15 days at 16°C and 27 days at 10°C). When the irradiance was 36 μmol m −2 s −1, the ash-free dry weight biomass of both species was about 80% lower than at 416 μmol m −2 s −1 and the biomass was not affected by neighbouring plants. However, in the higher light treatment the presence of P. pectinatus suppressed the biomass of C. aspera by maximally 63%. The individual biomass of P. pectinatus at high initial plant densities was reduced by maximally 70% by other plants of the same species, but was not affected by C. aspera. It is concluded that P. pectinatus rather than C. aspera has an advantage in the phase of emergence during spring. Furthermore, under higher light conditions and high inorganic carbon concentrations P. pectinatus may be a better competitor for light than C. aspera, because of its canopy placement near the water surface.