Seasonal biomass and carbohydrate allocation in dioecious Hydrilla

The phenology of dioecious hydrilla (Hydrilla Verticillata (L.f) Royle) was studied to discern seasonal low points in the carbohydrate storage of this nonindigenous weedy aquatic plant, Hydrilla was sampled monthly from two o utdoor ponds (0.3 ha each) at the Lewisville Aquatic Ecosystem Research Fac ility (LAERF) in Lewisville, Texas, from January 1994 through July 1995. Mo nthly samples were dried to obtain biomass dry weight (g m(-2)) and analyze d for total nonstructural carbohydrates (TNC), free sugars, and starch. Res ults indicated the lowest amount of stored TNC occurred in July for 1994 an d in June for 1995, with stolen (6%), upper stem (6%), root crown (10%) and lower stem (11%). Tubers (65%) and turions (60%) exhibited their lowest TN C concentrations when the total plant stores of TNC were at their lowest po int. Biomass increased from May through September; regrowing from overwinte ring shoots and root crowns, but not tubers. In addition to the hydrilla po nd sampling, containers planted with hydrilla were harvested from January 1 995 through December 1990. Monthly samples were likewise analyzed for carbo hydrate storage. The lowest concentrations of stored carbohydrates occurred in June for both growing seasons. These studies provide more insight into the timing of major allocation shifts in the hydrilla seasonal growth cycle for the purpose of optimizing management techniques.