ECOLOGICAL PHYSIOLOGY OF THE LICHEN HYPOGYMNIA PHYSODES

Abstract

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 14C mostly remained in the polyol pool during the treatments, with relatively little entering the insoluble fraction. The substantial loss of previously fixed 14C during 7 days saturation was almost entirely from the methanol soluble fraction. Within the insoluble fraction, there was also no loss of 14C during the 7‐day period if protein had been previously labelled with 14C‐leucine. Two other lichens, Xanthoria aureola and Peltigera horizontalis, also showed broadly similar declines to Hypogymnia physodes in various physiological characteristics.

The effect of abscisic acid on chlorophyll fluorescence in lichens under extreme water regimes

“…This difference from our results may be caused partly by an approx. four to five times higher ratio of thallus dry weight per ml buffer used by Farrar (1976a). A doubling of the ratio in our experiments at low temperatures led to a slight but significant decrease in the fluorescence yield (data not shown).…”

“…The decline in photosynthesis and chlorophyll fluorescence may be caused by damage due to anoxia (Farrar, 1976a) and may be increased by oxygen depletion in the medium, which could be stronger at a high density. Beyond that, high temperature stress may cause severe physiological damage to cell membranes (Kershaw, 1985).…”

“…Alternating periods of drying and wetting appear to be necessary for the persistence of a stable symbiosis (Farrar, 1976b ;Nash, 1996). After prolonged saturation some damage can be observed, which may be caused by oxygen deficiency (Farrar, 1976a). In addition, sensitivity to prolonged saturation is temperature-dependent (Ried, 1960a ;Farrar, 1976a).…”

“…After prolonged saturation some damage can be observed, which may be caused by oxygen deficiency (Farrar, 1976a). In addition, sensitivity to prolonged saturation is temperature-dependent (Ried, 1960a ;Farrar, 1976a). Dietz & Hartung (1998) investigated abscisic acid (ABA) contents in different lichen thalli in relation to their water content.…”

Carbon Dioxide Exchange in Lichens

“…Studies of photosynthesis in lichens have been made by a variety of techniques including the measurement of "C uptake (6)(7)(8), changes in gas volume both by manometry (17), a cartesian diver system (16), and 02 concentration with an 02 electrode (2).…”