Manganese toxicity in epiphytic lichens: chlorophyll degradation and interaction with iron and phosphorus

Abstract

Concentrations of chlorophylls a and b decreased with increasing MnCl 2 supply in the epiphytic lichen Hypogymnia physodes, but not in Lecanora conizaeoides. The reduction of chlorophyll concentrations in H. physodes was as strong (chlorophyll a) or even stronger (chlorophyll b) as in samples treated with CuCl 2. FeCl 3 compensated for MnCl 2-induced chlorophyll degradation in H. physodes. Furthermore, MnCl 2-induced growth inhibition of soredia cultivated on agar plates was alleviated by FeCl 3. These results suggest that Mn causes intracellular Fe deficiency in H. physodes. A soredia growth test with MnCl 2 and KCl in combination proved that mitigating effects of FeCl 3 were not just caused by reduced chemical activity of Mn 2+ due to the addition of another salt. Furthermore, the test showed that Cl − did not inhibit soredia growth. High FeCl 3 concentrations applied alone or in combination with MnCl 2 were even more detrimental to H. physodes than MnCl 2. MnCl 2 did not affect the concentrations of ATP, ADP and AMP in H. physodes. This suggests that Mn uptake does not induce intracellular P deficiency in H. physodes despite that Mn is known to be immobilized with P in H. physodes in intracellular polyphosphate granules and in extracellular encrustations.