Chapter 9 Trace metals, other chemical elements and lichen physiology: research in the nineties

Lichens are associations of two or more components: the alga and/or cyanobacterium, the photobiont partner, and the fungus, the mycobiont partner. The application of lichens as effective biomonitors of chemical contamination is based on investigations of stress-induced modifications of elemental content and physiological response. Stress derives from excessive amounts of chemical elements accumulated in the lichen, in addition to the leakage of essential nutrients. This chapter deals with the elemental content of the entire thallus. Physiological modifications on the other hand reflect the status of either photobiont, mycobiont, or both bionts. The present review focuses on the linkage of elemental content with lichen physiology and emphasizes research performed in the nineties. As such, this chapter does not report of many of the basic studies performed one to three decades ago, nor of recent studies which dealt with the physiological response to chemicals, e.g. fumigation studies but did not relate to the elemental content. Thus, the present chapter describes the following subjects: (1) the effect of chemical elements on the production of stress-ethylene in lichens; (2) elemental content and chlorophyll integrity in lichens; (3) elemental content and the spectral reflectance response of the lichen thallus; (4) chemical pollutants and changes in modulated chlorophyll a fluorescence: monitoring photosystem II (PSII) activites in lichens exposed to pollutants; (5) elemental content and degradation of cell membranes in lichens; (6) the accumulation of chemical elements and other physiological parameters: (ATP (adenosine triphosphate), malondialdehyde, amino acids and protein biosynthesis; (7) heavy metals as substrate and as "lichen killers". Of the 142 references cited in the present chapter, 87 (61%) were published in the years 1990-1999.