The relationship between moisture content and net assimilation rate of lichen thalli and its ecological significance

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Abstract
The relationship between net assimilation rates and percentage thallus saturation has been investigated in 12 widely occurring lichen species in southern Ontario. Optimum net assimilation rates occur between 35 and 70% of thallus saturation levels for different species. A close relationship has been shown to exist between their ecology and the percentage saturation at which maximum assimilation occurs. Optimum net assimilation rate values range from 0.03 mg CO2/g dry weight in Umbilicaria mammulata up to 0.11 mg CO2/g dry weight in Peltigera praetextata. Five of the species also exhibit a plastic physiology in that maximum net assimilation occurs at different levels of thallus saturation in replicates collected from different microhabitats. The implications of this variability are briefly discussed.