Interactive Influences of Selected Environmental Variables on Growth and TuberFormation in Hydrilla

摘要

In a 5-week greenhouse investigation, variations in the growth of both moneciousand dieocious Hydrilla (Hydrilla verticilata (L. f.) Royle) were compared over a range of temperatures (12 to 32 C) on a fertile inorganic sediment and on a infertile organic sediment. For these biotypes, total biomass production was severely restricted at 16 C and below, with thermal optima for growth occurring between 28 and 32 C. Total biomass, shoot number, and shoot length for each biotype were greater on the inorganic sediment than on the organic sediment. At higher temperatures, dioecious Hydrilla lengthened more extensively than monecious Hydrilla; however, the latter produced higher shoot densities and tuber numbers under most experimental conditions. Monecious Hydrilla appears to be better adapted to moderate temperatures than dioecious Hydrilla, and its potential distribution may include sediments less favorable for growth of the dioecious biotype. In a separate investigation conducted in two 10-week phases, biomass and tuber production in dioecious Hydrilla were examined under controlled environmental conditions, over a range of temperatures (20 to 30 C), under contrasting 10-hr (short) and 14-hr (long) photoperiods. (rh)