GROWTH OF DIOECIOUS HYDRILLA IN SEDIMENTS FROM 6 FLORIDA LAKES

Dioecious hydrilla (Hydrilla verticillata (L.f.) Royle) was cultured o utdoors in tanks in south Florida for four separate 16-week culture pe riods using sediments collected four different times from two sites ea ch in East Lake Tohopekaliga, Lake Tohopekaliga, Cypress Lake, Lake Ha tchineha, Lake Kissimmee and Lake Okeechobee. Differences in growth of hydrilla as determined by dry weight occurred both for between- and w ithin-lake sediment collection times. Total dry weight of hydrilla pla nts cultured in sediments from Site 2 in Cypress Lake for the first th ree culture periods produced an average of 73 g, 203 g, and 99 g per c ulture container and was higher than plants cultured in any of the oth er sediments. For the fourth culture period, however, dry weights of h ydrilla cultured in sediments from both sites in Lake Hatchineha were similar to those cultured in sediments from Site 2 in Cypress Lake. Dr y weight of hydrilla cultured in sediments from East Lake Tohopekaliga , Lake Kissimmee, and Site 1 of Lake Okeechobee was consistently low f or the four culture periods. For example, hydrilla cultured on sedimen ts from Site 1 in Lake Okeechobee produced an average of 4 g, 14 g, 4 g, and 2 g per culture container during the four culture periods. Subt erranean turions (tubers) were produced during two of the culture peri ods. The highest number of tubers, equivalent to 1,253 and 1,976 tuber s per m(2), were produced in sediments from Sites 1 and 2 of Cypress L ake, respectively, during December 5, 1988 to March 27, 1989. Individu al tuber weights averaged 50 mg each and were similar for all sites in all lakes for both culture periods. The ratio of root:shoot dry weigh t was less than 1 for hydrilla plants cultured on sediments from the s ix lakes for all four culture periods except for Site 1 in East Lake T ohopehaliga and Sites 1 and 2 in Lake Kissimmee during the July 6 to O ctober 26, 1987 culture period. High dry weight values were related to low root:shoot ratios and low hydrilla weights to high ratios. These data suggest that substantially different amounts of hydrilla growth c an be expected to occur both within and among in these six Florida lak es.