Nitrogen cycling in the Anemonia viridis symbiosis

[摘要] The temperate sea anemone, Anemonia viridis forms an endosymbiosis with dinoflagellate algae, or zooxanthellae. Previous studies of this and other symbioses have shown that zooxanthellae photosynthesis can allow them to be autotrophic with respect to carbon. Under environmental conditions where the anemone can satisfy its carbon requirements autotrophically, excretory nitrogen is also retained. In addition to this, Anemonia viridis is able to take up ammonium from seawater. Ammonium uptake has been observed in all classes of microalgal-invertebrate symbiosis, but has not been demonstrated in non-symbiotic species or aposymbiotic individuals. Ammonium uptake is also known to be linked with photosynthesis, since it only takes place in the light or after a period of exposure to light. Whether ammonium is recycled between the zooxanthellae and host or is conserved by the host remains unresolved. Whatever the mechanism by which ammonium is assimilated, it was not known whether ammonium uptake could support growth. To examine this question, symbiotic anemones were maintained for three months in seawater supplemented with 20muM ammonium and weight change was compared with that of control anemones in unsupplemented seawater. During this experiment, anemones in seawater lost weight whereas those in ammonium-supplemented seawater increased in weight. This provided a preliminary indication that ammonium uptake could support growth.

[发布机构] University:University of Glasgow

[关键词] Physiology