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 Vallisner ia americana was significantly related to the depth of the 1% of surfa ce irradiance (Z) and the photosynthetic photon irradiance calculated for each shading treatment imposed during this study. Between the rang e 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, a nd mass of individual winterbuds ranged from 0.18 to 0.04 g. Total bio mass of winter buds produced was reduced when plants were exposed to a 14-day period without irradiance during the middle of the growing sea son. Applying the results of the culture experiments to conditions fou nd in Navigation Pool 8 of the Upper Mississippi River suggests that i rradiance may indeed limit the distribution and abundance of Vallisner ia americana by reducing the number and size of winter buds. (C) 1997 Elsevier Science B.V.