NITROGEN AND PHOSPHORUS UPTAKE IN SEEDLINGS OF THE SEAGRASS AMPHIBOLIS-ANTARCTICA IN WESTERN-AUSTRALIA

The uptake of nitrate, ammonium and phosphate was examined in vitro in seedlings of the seagrass Amphibolis antarctica ((Labill.) Sonder ex Aschers.). Uptake of all three nutrients was significantly correlated with external concentration up to 800 mu g l-1. The uptake of nitrate (0-200 mu g NO3 -N g dry wt-1 h-1) was significantly lower than the up take of ammonium (0-500 mu g NH4 -N g dry wt-1 h-1), suggesting that t he seedlings have a higher affinity for this form of nitrogen in the w ater column. Data were in general agreement with uptake rates recorded for other seagrasses, notably Zostera marina. In comparison to the do minant macroalgae for the same region, seedlings had either similar or higher uptake rates in relation to external concentration, lending su pport to the hypothesis that seedlings, which do not possess roots, be have like macroalgae in terms of nutrient acquisition from the water c olumn. A comparison with literature data on adult seagrass, however, t hat seagrasses show lower uptake rates than macroalgae suggesting that the macroalgae, which are totally reliant on the water column for nut rients, are more efficient at uptake than seagrasses which may potenti ally use the sediment for a nutrient source.