Interaction between ammonium and phosphate uptake rates in the seagrass Zostera noltii

Abstract

Foliar ammonium and phosphate uptake rates and their interactions were assessed in whole seagrass Zostera noltii plants incubated in 2-compartment transparent chambers. This method allowed the calculation of nutrient uptake rates by leaves and by roots and rhizomes independently, avoiding plant breakage. Overall, a direct linear relationship between foliar uptake rates and seawater nutrient concentrations (phosphate or ammonium) was found, with uptake rates much higher in the first 5 min (nutrient adsorption). This faster adsorption was followed by slower uptake rates (nutrient absorption) in the next time intervals. When both nutrients were supplied separately, foliar ammonium uptake rates were 3-fold higher than those of phosphate in the range of the nutrient concentrations assayed for the whole incubation interval (120 min). When both nutrients were added simultaneously (10 μM phosphate and 50 μM ammonium, final concentrations), ammonium uptake rates were similar to those values recorded when ammonium was provided alone, whereas phosphate uptake rates were about 55% lower than those measured when phosphate was added alone. This study reveals for the first time the inhibitory effect of ammonium on phosphate uptake in seagrasses. © Inter-Research 2013.