The Uptake and Metabolism of Phosphate by the Lichen Hypogymnia Physodes

SUMMARY Hypogymnia physodes showed active uptake of inorganic phosphate (Pi) from, very dilute solutions (less than IO5 nmol Pi dm‐3). Approximate values of Vmax and Km compare with published data for phloem and maize roots. Pi absorbed from these dilute solutions was not exchangeable, but that absorbed from solutions of IO5–IO6 nmol Pi dm‐3 was exchangeable. There was some evidence, but not conclusive, that two types of uptake mechanism existed. The metabolism of absorbed Pi was similar to that described in other lichens and included appreciable incorporation into a fraction which may be largely polyphosphate. The ecological significance of this is discussed. Calculations based upon the reported concentration of Pi in rainwater, rates of uptake of Pi by H. physodes from solutions of equivalent concentration, and growth rate (as an indicator of Pi needs) show that the lichen would only need one hour of rain per week to maintain its phosphorus status. It is therefore unlikely that phosphorus limits the growth of the lichen in nature.