Utilization of freshwater and ocean water by coastal plants of southern Florida.

Plants toward the interior of the keys were generally using freshwater while those toward the edge were using ocean water. A plot of the hydrogen and oxygen isotopic composition of the plant water yielded a mixing line between typical freshwater values and those of ocean water. In general, the isotopic ratios of stem water for species found in hardwood hammocks were confined to the freshwater end of the line, followed by values of stem water from mangrove margin species. Species found in mangroves, however, had water with extremely variable isotopic ratios, ranging from values typical of ocean water to values typical of freshwater. This variability is consistent with the hypothesis that mangroves are fully capable of growing in freshwater, but are limited to saline habitats because of competitive exclusion by fast-growing glycophilic plants.-from Authors