Plants--Effect of phosphorus on

Recent evidence indicates P-limitation in tropical seagrass beds, but to date no data are available on P kinetics of the dominant tropical seagrass Thalassia testudinum. In this study, T. testudinum leaves and roots exhibited Michaelis-Menten saturation kinetics under high (0.5 to 25 muM SRP) and low (0.5 to 5 muM SRP) P concentrations. Leaf Vmax was similar under light and dark conditions. Root Vmax under the high range was slightly lower (30%) in the dark and 2 to 3-fold lower than leaves in the light and dark. Leaf and root P uptake rates were similar at low substrate concentrations. A two-phase kinetic system appears to be functioning with lower values of leaf Vmax and Km at low P levels, indicating a higher affinity for P by leaves at lower P concentrations. In conclusion, T. testudinum leaf and root tissues may contribute similarly to plant P uptake at low concentrations.