Lichen respiration in relation to active time, temperature, nitrogen and ergosterol concentrations

1. Respiration in eight lichen species was related to thallus hydration sta tus, external temperature and to total nitrogen, chitin and ergosterol conc entrations. Chitin is a nitrogenous and major compound of the fungal cell w all, and ergosterol is a sterol of the plasma membrane in fungi and sometim es in algae. 2. Hydration of previously dry thalli resulted in an initially high rate of respiration. Both the amplitude of this resaturation respiration and the t ime required to reach steady state varied among species. Generally, peak ra tes were one to three times higher than steady-state rates, which were reac hed 3-7 h after hydration, 3. Increases in external temperature also resulted in transient bursts in r espiration. Again, both the amplitude of the burst and the time required to reach steady state varied among species. Also depending on species, a temp erature increase from 5 to 15 degrees C resulted in two- to fivefold increa ses in steady-state respiration. 4. Steady-state respiration, at optimal thallus hydration and a given tempe rature, varied three- to sixfold among the species, when related to thallus dry mass. This difference correlated best (r(2) = 0.89) with their ergoste rol concentration, where a doubling in ergosterol resulted in more than a d oubling in respiration. Respiration correlated less well to total nitrogen or chitin. 5. The chitin to ergosterol ratio varied more than one order of magnitude b etween the species, where species with high nitrogen concentrations had the highest ratio. This implies that species with access to ample amounts of n itrogen can make more fungal cell walls in relation to plasma membrane surf ace area.