are vallisneria hetrotrophic?
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A shading experiment was conducted over a growing season to measure the effects of light reduction on Vallisneria americana in Perdido Bay on the Florida–Alabama border and to determine the response of heterotrophic bacteria in the rhizosphere. Plants subjected to 92% light reduction showed the most pronounced effects in chlorophyll a concentration, above- and below-ground biomass, and leaf dimensions. These results further suggested that the V. americana life cycle, as exhibited in temperate waters, was impaired. Heterotrophic bacteria were enumerated and identified (i) from the roots and sediments of fully illuminated plants and from unvegetated sediments at three intervals and (ii) from the roots of plants that have been subjected to 92% light reduction for 3 months. Up to two orders of magnitude greater numbers of bacteria were enumerated from root samples than sediment samples on a dry weight basis. Bacteria enumerated from the roots of plants subjected to light reduction (1.3±1.1×108 CFU g−1) were significantly higher than numbers of bacteria enumerated from the roots of fully illuminated plants (4.8±1.8×107 g−1 in the summer) or