SYMBIOSIS - Cyanobacteria - page 367

is typically found on the tree trunks of Abies balsamea (Balsam fi r) in Canada and at times on Picea
mariana (black spruce) and P . glauca (white spruce) and rarely on Acer rubrum (red maple). It is
listed in the endangered wildlife in Canada and also critically endangered globally and listed on
IUCN Red List of Threatened Species. The natural disturbances that affect its population are stand
scenescence, forest blow down, insect outbreaks and grazing by invertebrates. Along with any
one of these, anthropogenic activities/disturbances such as wood harvesting, urban development,
fi re, air pollution, pesticides and climatic changes may act together. A fi ve-year management plan
(2006-2011) for the boreal felt lichen in Newfoundland and Labrador has been prepared by the
Wild Life Division, Department of Environment and Conservation in collaboration with Boreal Felt
Lichen Working Group. The possible management strategies for the preservation of cyanolichens in
northeastern North America have been highlighted (Richardson and Cameron, 2004).
Goward and Arsenault (2000b) proposed the existence of a “dripzone effect” by which nutrients
that leach from the upper branches of Populus enhance the pH of the neighbouring conifers. Due to
this Lobaria pulmonaria and other epiphytic cyanolichens attain their maximum development over
the lower branches of conifers. This phenomenon seems to be prevalent in the forests of humid
regions of south-central Columbia that are not subjected to acid rain. Arsenault and Goward (2000)
further emphasized that aspen and cottonwood should be considered trees of keystone nature as they
effi ciently pump nutrients from soil to the canopy and later release these to nearby pines altering
the acidic pH of the bark of pines that is otherwise unsuitable for the growth of cyanolichens. In
support of this they indicated that the copious presence of cyanolichens over the bark of pines,
spruces, hemlocks and other members of the Pinaceae in some portions of North America. Though
the proposed hypothesis of “dripzone effect” needs experimental evidence, it may derive logical
support from the fact that decreasing numbers of aspens contribute to the general loss of epiphytic
macrolichen diversity on conifers.
In a conservation strategy, transplantation of over 1000 mature thalli of Lobaria oregana and
Pseudocyphellaria rainierensis has been done into the crowns of old-growth (400-700 year), mature
(140-150 year), young (30-40 year) and recent clear-cut areas of Oregon Cascades. Since the growth
rates were very much lower in clear-cuts due to high (50-90%) mortality rates, it is suggested to
include young forests in conservation strategies (Sillett and McCune, 1998). In order to increase
biodiversity of lichens in managed forests in Pacifi c North West, Sillett and Goslin (1999) advocated
the retention of remnant trees, maintenance of hardwoods followed by longer rotation periods to
conserve old-growth associated lichens. Alternative silvicultural practices are receiving attention
in view of decreasing populations of aspen ( Populus tremula ) that supports growth of epiphytic
lichens. The rate of removal of aspen was nearly up to 50%. Cyanolichens Collema curtisporum , C .
furfuraceum and Leptogium saturinum can be suitably preserved if selective thinning of aspens is
conducted (Hedenås and Ericsona, 2003).
VII. BRYOPHYTES
Of the 340 known genera of liverworts, only two of them form symbioses with cyanobacteria. These
are Blasia pusilla and Cavicularia densa belonging to Blasiales. Among the six hornworts, fi ve of them,
i.e. Anthoceros , Dendroceros , Notothylas , Phaeoceros and Leiosporoceros form symbiotic association with
cyanobacteria (Rai et al ., 2000; Adams, 2000; Villarreal and Renzaglia, 2006; Adams and Duggan,
2008). In most of these, the symbiont is a species of Nostoc . Granhall and Hofsten (1976) reported
intracellular localization of Nostoc fi laments in a species of Sphagnum from Swedish mires. Pleurozium