XVI International Botanical Congess

Field/laboratory studies demonstrate density-dependent physiological plasticity in Hydrilla verticillata (Hv) and Myriophyllum spicatum (Ms).Standing crop biomass (SCB)and CO2 compensation point(CCP)of Hv, and [CO2], [HCO3-], [O2], and pH were measured in three lakes. The SCB was negatively related to CCP, [CO2] and [HCO3], and positively related to [O2] and pH. Both were grown at densities from 1 to 16 individuals /100 cm2. The CCP of both was negatively related to density. High density grown Ms exhibited twofold greater CO2 uptake-rate at high [CO2] compared to low-density plants. The equation (w = Wmax (1 + a N)-b) and a modified version (w^ = Wmax (1 + a N)-b^, where b^ = 1/log N were applied to Hv growth data. The modified equation incorporated physiological plasticity and better predicted experimental data. Density dependent physiological plasticity can be incorporated into a population model.