Cultured phycobionts of various epiphytic lichens were exposed to aqueous solutions of either sulfite, nitrite, sulfate, or nitrate, simulating an acute pollutant stress for a short time. The impact of these pollutants was determined by measuring the chlorophyll content and the14C-incorporation rates. Nitrate and sulfate proved to be nontoxic at pH 4, whereas distinct differences were noted in the sensitivity of the various phycobionts to sulfite and nitrite. In many of the species examined there were clear correlations with data available on the sensitivity of the whole lichen thallus. In some species, however, the phycobiont was either distinctly less sensitive or less tolerant than would be expected from ecological studies on the geographical distribution of the lichen.
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