Ecological Physiology of the Lichen Hypogymnia Physodes

SUMMARY The effect of constant saturation with water upon Hypogymnia physodes for periods of up to 7 days was investigated in either light or dark, at either 20°C (representative of most laboratory experiments on lichen physiology) or 5°C (more representative of field conditions). In all cases the capacity for photosynthesis, phosphate uptake, and total polyol content declined over 7 days; the decline was greater at 20°C than 5°C, and usually greater in the dark than in the light. In general, both alga and fungus reacted similarly to the treatments. Previously fixed 14 C mostly remained in the polyol pool during the treatments, with relatively little entering the insoluble fraction. The substantial loss of previously fixed 14 C during 7 days saturation was almost entirely from the methanol soluble fraction. Within the insoluble fraction, there was also no loss of 14 C during the 7‐day period if protein had been previously labelled with 14 C‐leucine. Two other lichens, Xanthoria aureola and Peltigera horizontalis , also showed broadly similar declines to Hypogymnia physodes in various physiological characteristics.