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Phosphorus uptake kinetics of a dominant tropical seagrass Thalassia testudinum
Gras, A.F.; Koch, M.S.; Madden, C.J. (2003). Phosphorus uptake kinetics of a dominant tropical seagrass Thalassia testudinum. Aquat. Bot. 76(4): 299-315.
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

Available in  Authors 

    Kinetics; Limiting factors; Nutrient cycles; Nutrients (mineral); Phosphorus; Pore water; Sea grass; Surface water; Thalassia testudinum K.D.Koenig, 1805 [WoRMS]; ASW, USA, Florida, Florida Bay [Marine Regions]; Marine
Author keywords
    phosphorus; nutrient uptake; seagrass; nutrient cycling; kinetics

Authors  Top 
  • Gras, A.F.
  • Koch, M.S., correspondent
  • Madden, C.J.

    Although nitrogen is primarily the dominant nutrient limiting seagrass production in temperate estuaries, phosphorus (P) limitation can be important in tropical carbonate-dominated seagrass systems. While nitrogen uptake kinetics of seagrasses are moderately well established, very limited data exist on the dynamics of P-uptake. In this study, we determined the kinetics of dissolved inorganic phosphorus (Pi uptake for a dominant tropical seagrass Thalassia testudinum across a range of Pi levels (0.5-25 μM). Under this broad range, leaf Pi-uptake (μmol g-1 dw h-1) rates were similar under light (Vmax = 1.90) and dark (Vmax = 2.10) conditions, while root Pi-uptake rates declined 30% in the dark, and were significantly lower than leaves under both light (Vmax = 0.57) and dark (Vmax = 0.38) conditions. At lower Pi concentrations (0.5-5.0 μM), leaf Vmax was 2-3-fold lower (0.50-0.77), while root Vmax was the same at high and low Pi ranges. Based on linear and non-linear models of Pi-uptake kinetics for T. testudinum, leaves can contribute a majority of the P sequestered by the plant when surface and porewater Pi levels are equally low (0.05-0.5 μM). Based on the calculated P-demand of T. testudinum in South Florida, solely root or leaf uptake can account for the P requirements of T. testudinum when porewater or surface water Pi levels are 0.5 μM. However, when surface and porewater Pi levels are extremely low (<0.10 μM), such as in Florida Bay and other carbonate seagrass systems where Pi sequestration by the sediment is highly efficient, even root + leaf Pi-uptake rates do not meet the P requirements for growth and P-limitation may occur.

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