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

Abstract

Summary 1.Respiration in eight lichen species was related to thallus hydration status, external temperature and to total nitrogen, chitin and ergosterol concentrations. Chitin is a nitrogenous and major compound of the fungal cell wall, and ergosterol is a sterol of the plasma membrane in fungi and sometimes 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 time required to reach steady state varied among species. Generally, peak rates were one to three times higher than steady-state rates, which were reached 3-7 h after hydration. 3. Increases in external temperature also resulted in transient bursts in respiration. Again, both the amplitude of the burst and the time required to reach steady state varied among species. Also depending on species, a temperature increase from 5 to 15°C resulted in two-to fivefold increases in steady-state respiration. 4. Steady-state respiration, at optimal thallus hydration and a given temperature, varied three-to sixfold among the species, when related to thallus dry mass. This difference correlated best (r 2 = 0·89) with their ergosterol concentration, where a doubling in ergosterol resulted in more than a doubling in respiration. Respiration correlated less well to total nitrogen or chitin. 5. The chitin to ergosterol ratio varied more than one order of magnitude between the species, where species with high nitrogen concentrations had the highest ratio. This implies that species with access to ample amounts of nitrogen can make more fungal cell walls in relation to plasma membrane surface area.

Photosynthetic traits of freshwater lichens are consistent with the submersion conditions of their habitat

“…In freshwater lichens, the Chla to ergosterol ratio was similar in the four species investigated (around 0.6, Table 1). Values for Chla, b and ergosterol in freshwater lichens were in the range of those previously found for non-aquatic lichens (Demmig-Adams et al, 1990;Sundberg et al, 1999).…”

“…Ergosterol is the major sterol of the fungal plasma membrane and is used as an indicator of the relative proportions of metabolically active fungal cells in lichens (Sundberg et al, 1999), while Chla may serve as a marker of total photobiont cells (Descy and Metens, 1996;Palmqvist et al, 1998). In freshwater lichens, the Chla to ergosterol ratio was similar in the four species investigated (around 0.6, Table 1).…”

Rehydration of the LichenRamalina laceraResults in Production of Reactive Oxygen Species and Nitric Oxide and a Decrease in Antioxidants

“…In species that, like R. lacera, contain Trebouxia sp. photobionts (C. islandica, H. physodes, Lasallia pustulata, and Platismatia glauca) the initial respiration rate was always 1.5 to 3 times higher than that in the final steady state that was reached within 3 to 7 h after immersion in water (60). It was proposed that the initially high respiration rate is the result of uncoupling of the mitochondrial electron transport chain or of a burst in respirable substrates related to drought damage of membranes.…”

Tansley Review No. 117

“…Lichens with high thallus C : N ratios have the lowest rates of respiration both when related to area and when related to dry weight (Fig. 1c,d) (Sundberg et al, 1999a). This implies that species with low respiration might be relatively rich in carbon compounds that contribute to biomass but with low metabolic turnover and energetic requirements.…”

“…Indeed, and as for plants, lichen respiration increases with thallus nitrogen concentration, being an effect of increased energy demand related to protein turnover (Lambers, 1985). However, for lichens this relation is less tight because of the nitrogen content of chitin, which does not turn over as rapidly as proteins (Sundberg et al, 1999a).…”