Monoecious Hydrilla verticillata development in complete darkness

Abstract

Hydrilla verticillata is one of the most problematic invasive submersed aquatic weeds in the United States. A study was conducted in growth chambers to look at aspects of development of monoecious Hydrilla verticillata in complete darkness. A single tuber was placed in each of forty-eight growth chambers. Following differential blackout intervals of zero, two, four, six, eight, or ten weeks, plants in each treatment group were dissected into above ground (shoot) and below ground (tuber) material. Plant section length, dry weight, and non-structural carbohydrate content were determined. Shoot lengths increased by 32.1 cm following ten weeks of dark exposure, as compared to the zero-darkness exposure controls. Despite the increase in total shoot length, total dry weight decreased from 34.6 mg (zero-darkness) to 25.4 mg after ten weeks of dark exposure. During this time, tuber dry weight declined from 34.6 mg (zero-darkness) to 5.8 mg and shoot dry weight increased from 0 mg (zero-darkness) to 20 mg. Starch was the most prominent non-structural carbohydrate present in plants throughout the experiment. Starch levels were highest in plants prior to germination (31% of dry weight) and declined significantly and steadily over the course of the 10-week dark development experiment to an average of 20% of dry weight. The results of this study indicate that monoecious hydrilla has a high elongation and development potential over long periods of time in darkness. This adaptation is advantageous in overcoming light blocking management techniques and in allowing the species to occupy a larger area of the profundal zone.