Manganese as a site factor for epiphytic lichens

Abstract

The effect of Mn on the viability of the epiphytic lichens, with special reference to Hypogymnia physodes, was studied. In Chapter 1 a general introduction to metal adsorption and toxicity in lichens is presented. Chapter 2 discusses the influence of Mn on soredia in H. physodes and interaction with Ca and Mg. The chapter is based on culture experiments with soredia at 7 µM and 7 mM Mn. Soredia growth and chlorophyll concentrations were studied. Element distribution in the soredia was determined with X-ray microanalysis and simultaneously structural changes were studied with TEM and SEM. Chapter 3 focusses on element microdistribution in soredia of H. physodes cultivated at 500 µM for varying cultivation periods. Element content was studied with x-ray microanalysis combined with TEM. Chapter 4 examines ultrastructural changes in soredia of H. physodes, cultured at different Mn concentrations (7 µM, 500 µM and 7 mM Mn).Chapter 5 studies extracellular adsorption and intracellular uptake in thalli of H. physodes and Lecanora conizaeoides. In addition, conversion of Mn2+ to insoluble Mn3+ and Mn4+ in the apoplast was studied. Chapter 6 deals with the element distribution in thalli of Mn supplemented and unsupplemented H. physodes and L. conizaeoides on a subcellular level. Furthermore, thallus structures were observed with a TEM and SEM. Chapter 7 is about the influence of Mn on the chlorophyll concentrations in thalli of H. physodes and L. conizaeoides incubated with Mn alone or in combination with Ca, Mg or Fe. Further, the effect of Mn on ATP concentrations was studied in thalli of H. physodes to test the hypothesis that high Mn concentration cause intracellular P deficiency. Chapter 8 studies Mn adsorption and uptake in the beard lichens Alectoria sarmentosa and Bryoria fuscescens. Simultaneously, effects of Mn on membrane integrity was investigated.Chapter 9 focusses on Mn adsorption and uptake in the cyanolichens Leptogium saturninum, Lobaria pulmonaria and Nephroma helveticum. Chapter 10 studies effects of Mn on chlorophyll parameters in the chlorolichen H. physodes and the cyanolichens L. saturninum, L. pulmonaria and N. helveticum. Parameters studied were Φ2, NPQ, qN and qP. Chapter 11 compares effects of excess Mn on the photobionts of H. physodes, L. conizaeoides, L. saturninum, N. helveticum and L. pulmonaria by means of fluorescence microscopy.Decreasing abundance of epiphytic lichens with increasing Mn supply from the sub­strate or from stemflow was found in several coniferous forests of Europe (Germany) as well as western (Montana, British Columbia) and eastern North America (New York State). Experiments carried out with H. physodes and other species of chloro- and cyano-lichens suggests that these correlations are causal. High Mn concentrations, e.g., reduce chlorophyll concentrations, chlorophyll fluorescence and degrade the chloroplast in lichen photobionts. Excess Mn inhibits the growth of soredia of H. physodes and causes damage in the fine- and ultra-structure of the soredia. Adult lichen thalli remain structurally unaffected by Mn. Mn uptake does not result in membrane damage. Ca, Mg, Fe and perhaps also Si alleviate Mn toxicity symptoms in H. physodes. L. conizaeoides is not sensitive to Mn both in laboratory experiments and in the field. The data suggest that high Mn concentrations are an important site factor for epiphytic lichens in coniferous forests that has been overlooked until recently.