R. Figueira et al., Natural levels of saline elements in lichens: Determination of cellular fractions and their importance as saline tracers, LICHENOLOGI, 31, 1999, pp. 183-196
Using a sequential elution procedure, the cellular location of Cl-, Na+, Mg
2+, K+ and Ca2+ was determined in the lichen Ramalina canariensis from the
southwest coast of Portugal. After a dry deposition period, a logarithmic d
ecease in the extracellular (surface and wall-bound) concentration of Cl-,
Na+ and Mg2+ was observed with increasing distance from the coast. The impo
rtance of each cellular fraction as an indication of the airborne salts was
identified using factorial analysis methods, as was the relationship betwe
en the extracellular and intracellular concentration of the saline elements
. The factorial analysis showed that the most important elements for the bi
omonitoring of airborne salinity were Cl-, Na+ and Mg2+. However, for the c
ations, only the surface and wall-bound (for Na+) fractions seem to be rela
ted to sea-salt deposition on the lichens. The intracellular fractions of t
hese elements are relatively independent of the surface and wall-bound conc
entrations, or reflect some non-linear processes induced by extreme extrace
llular concentrations. Although they may represent a significant proportion
of the total element concentration, intracellular element concentrations a
re of little value in monitoring salt deposition, due to physiological cont
rol by the organism. The use of rural analyses, without any fractional diff
erentiation, can be a biased method for biomonitoring the accumulation of s
alt spray by lichens, because it includes the intracellular fraction, which
may be independent of the deposition taking place. The use of the differen
t cellular fractions provides a more informative indication of the depositi
on of atmospheric elements, while also giving information on any physiologi
cal alterations induced by the specific environmental chemical factors, inc
luding membrane damage. (C) 1999 The British Lichen Society.