The Ecophysiological Response of Two Invasive Submerged Plants to Light and Nitrogen.

Two submerged species have small differences in their ecophysiological responses when exposed to individual environmental factors. However, field observations showed that under eutrophic conditions with low light availability, could be displaced by . Here we investigated the combined effect of environmental factors on the ecophysiological response of the two species in order to explain the differences in their invasion successes. We cultivated the plants in aquaria containing five different nitrogen (N) concentrations and incubated at five different light intensities. For both species increasing nitrogen concentrations resulted in increased relative growth rate, chlorophyll concentration, and actual photochemical efficiency of photosystem II (Φ), however, they produced less roots. Lowering light intensity resulted in a lower relative growth rate, root production, and nutrient removal. In contrast, chlorophyll concentration in the leaves, and Φ increased. The main difference between the two species was that the light compensation point ( ) and weight loss in the dark were significantly higher and photochemical efficiency and chlorophyll concentration were significantly lower for than for , indicating that the latter can survive under much more shady and hypertrophic conditions. The change in nitrogen concentration of the media and in tissue concentration of the plants indicated that has a higher nitrogen removal capacity. The ecophysiological differences between the two species can be an explanation for invasion success of over and thus may explain why the latter is replaced by the first.