Kinetic parameters and organic phosphorus remineralization potential of alkaline phosphatase activity in the tropical seagrass Thalassia testudinum and associated epiphyton

Tropical carbonate estuaries are P-limited due to high carbonate sorption of DIP, therefore alternative P sources may represent an important contribution to the nutrient requirements of submerged aquatic vegetation. Alkaline phosphatase (AP'ase) is a cell-surface enzyme that allows aquatic plants to utilize the organic-P pool, and its activity (APA) may generate a significant portion of plant P-requirements in oligotrophic environments. Seasonal APA of the seagrass Thalassia testudinum and its epiphytic community was measured in NE Florida Bay. APA was higher for T. testudinum leaves with intact epiphytes (TTE) than for T. testudinum leaves alone (TT) in all seasons, and the spring growing season elicited the highest activities. Based on in situ PME levels (0.117--0.387muM), AP'ase P-remineralization rates were 0.326--2.181 for TTE and 0.237--0.823 for TT (mumol g-1 AFDW day-1), representing 26% and 4% of P-uptake, respectively. Therefore, APA may be an important P source to the seagrass-epiphyte consortium in tropical carbonate estuaries.