Environmental Engineering Reference
In-Depth Information
CHAPTER THREE
Lichens and industrial pollution
OLE WILLIAM PURVIS
Introduction
Lichens are composite organisms including at least one fungus (mycobiont)
and an alga or cyanobacterium (photobiont) living in a mutualistic symbiosis
(Hawksworth & Honegger
1994
). The lichen symbiosis may involve multiple
and different bionts, especially photobionts, at various stages of its life history
(Hawksworth
1988
; Jahns
1988
). Lichenised fungi are ecologically obligate
biotrophs acquiring carbon from their photobionts (Honegger
1997
). Lichens
colonize bark, rocks, soil and various other substrata, and occur in all terrestrial
ecosystems, covering more than 6% of the Earth's land surface. They are domin-
ant in Arctic and Antarctic tundra regions where they form the key component
of ecosystem processes, as a part of global biogeochemical cycles and also the
food chain. Arctic and sub-Arctic lichen heaths are readily visible from space
using remote sensing techniques and the effects of 'point source' smelters in
creating 'industrial barrens' and emission reductions leading to recovery of
Cladonia-rich heaths are well-documented (Tømmervik et al.
1995
,
1998
,
2003
).
Lichens play a major role in plant ecology and the cycling of elements, such
as C, N, P, heavy metals and radionuclides (Knops et al.
1991
; Nash
1996b
) and
are extremely tolerant of ionising radiation (Brodo
1964
). Lichens contribute
to soil formation and stabilization ( Jones
1988
). Lichenized fungi may well be
ancestral to fruit-body forming ascomycetes (Eriksson
2005
). There are around
13 500 known species and 18 000 20 000 estimated worldwide (Sipman &
Aptroot
2001
). The lichen habit is dispersed through many different ascomy-
cete and a few basidiomycete orders, and there is much convergent evolution
in thallus form (Grube & Hawksworth
2007
). Lichens play a significant role
in global processes, ecosystem function and the maintenance of biodiversity
(Hawksworth
1988
,
1991
,
2006
;Nash
1996a
; Gorbushina
2006
). Growth rates
tend to be slow varying from less than 1 mm to a maximum of a few centimetres
a year. Some are rapid colonisers of bare ground, including metal-contaminated
