Phosphorus uptake kinetics of a dominant tropical seagrass Thalassia testudinum
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770; e-ISSN 1879-1522, more
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| Keywords |
Chemical elements > Nonmetals > Phosphorus
Cycles > Chemical cycles > Geochemical cycle > Biogeochemical cycle > Nutrient cycles
Flora > Weeds > Marine organisms > Seaweeds > Sea grass
Limiting factors
Nutrients (mineral)
Physics > Mechanics > Kinetics
Water > Pore water
Water > Surface water
Thalassia testudinum K.D.Koenig, 1805 [WoRMS]
ASW, USA, Florida, Florida Bay [Marine Regions]
Marine/Coastal |
| Author keywords |
phosphorus; nutrient uptake; seagrass; nutrient cycling; kinetics |
| Authors | | Top |
- Gras, A.F.
- Koch, M.S., correspondent
- Madden, C.J.
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| Abstract |
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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