Effects of irradiance on growth and winter bud production by Vallisneria americana and consequences to its abundance and distribution

Number, total biomass, and individual mass of winter buds of Vallisneria americana was significantly related to the depth of the 1% of surface irradiance (Z) and the photosynthetic photon irradiance calculated for each shading treatment imposed during this study. Between the range of 23.8 and 111.2 cm depth for the 1% Z, total biomass of winterbuds produced ranged from 0.63 to 0.01 g, counts ranged from 3.5 to 0.1, and mass of individual winterbuds ranged from 0.18 to 0.04 g. Total biomass of winter buds produced was reduced when plants were exposed to a 14-day period without irradiance during the middle of the growing season. Applying the results of the culture experiments to conditions found in Navigation Pool 8 of the Upper Mississippi River suggests that irradiance may indeed limit the distribution and abundance of Vallisneria americana by reducing the number and size of winter buds.