Preamble.On the plain, are natural markers that are able to highlight the pollution of our habitat. Their mere presence may partially reassure us about the state of our land, water and air. These natural markers are: frogs, snails and bees. In the high mountains, the clearness of the sky, the purity of water and especially the absence of that horrible black cloak that covers our cities, it is usually sufficient to reassure us!
But there is another indicator of the ecosystem, very sensitive and precise, able to provide a more sensitive health of our mountains.
It is something very small that we usually do not notice and do not photograph, I appreciate its beauty only when highly magnified.
They are as important as forests or air currents that liberate us from the smog: they are the Lichens.
In winter, they color our images of yellow, orange, green and red. Even the rocks, of the highest peaks, are enhanced by the presence of lichens.
The Lichens.Lichens, often mistakenly associated with mosses, they are organisms rather unusual.
In fact, they are two different organisms (a fungus and an alga) living in symbiosis. The lichens have very ancient origins, in fact, have evolved into a independent manner of other organisms on the planet, including fungi and algae taken individually.
The benefits arising from the coexistence of a heterotroph (the fungus, as in the mold) with an autotrophic organism (algae or cyanobacteria) are manifold.
The fungus is able to extract water and minerals from the soil (rhizosphere) and the atmosphere in much more efficiently than it would the seaweed, the latter, however, can produce much more sugar molecules and complex as it is able to carry out photosynthesis.
All this translates into additional weapon in the fight for survival, such that 25% of all known fungi are lichenizzati.
Lichens are characterized by different growth forms, they constitute a first classification model.
:The crusty lichens - foliosa Lichens - fruticose Lichens - Lichens squamulose - The gelatinous lichens.
Lichens reproduce by vegetative or sexually.
-Reproduction by vegetative (or asexual) occurs due to the presence of special organs, and Soredi Isis, which, through the action of atmospheric agents, animal or human, in the spread of small clusters of hyphae and algae are ready to give birth to a new thallus lichens.
These organisms are highly resistant to extreme environmental conditions (lichens can be found both in Antarctica and the sunny deserts) but are extremely sensitive to air pollution, because, unlike the higher plants and other plants, have no mechanism expulsion of toxins. For this reason, the lichens are often used as indicators of air quality. The presence of lichens in a given location indicates a very low pollution rate.
Another peculiar feature of Lichen is their slow growth, which on average is calculated in millimeters per year; has known that lichen growth is slower Rhizocarpon geographicum, a fairly common lichen that grows on rocks, which employs a century to grow by only 4 mm.
Lichens as bioindicators.
Main features of Lichens
The main features of lichens that are good indicators of environmental pollution can be summarized in five points:
1) high capacity of absorption and accumulation of substances taken from the atmosphere. Lichens carry out gas exchange through their entire surface, being able to pick up water vapor from the air is not saturated even with an absorption that continues day and night to many years. It 'easy to understand why the lichens are able to accumulate significant levels in those resistant to atmospheric contaminants (metals, radionuclides, chlorinated hydrocarbons, fluorides) are unlikely to be measured in air samples. Nutrients and contaminants are taken in gaseous form, in solution or bound to the particles;
2) resistance to prolonged periods of slow dry lichens. In these methabolic conditions the protracted drought causes a deterioration of cells gonidiali. However, the protracted drought causes a deterioration of cells gonidiali. With increasing humidity many substances present in the atmosphere, result in progressive damage to the algal cells.
3) Resistance to temperature extremes. This allows a continuous lichen, even in winter, when levels of air pollution are generally higher.
4) Inability to regularly rid of old parts or poisoned, as is the case for higher plants.
5) Slow growth and great longevity of lichens. Factors that allow you to follow the evolution of pollution.
Lichens can be used to assess air quality thanks to their particular physiological characteristics.
The changes induced by air pollution on lichens are:
a) Reduction of the total number of species over time
b) Reduction of the total number of species in space
c) Increased coverage and greater presence in more polluted areas, such as city centers, the crusty lichens and fruticose than leafy.
d) Reduction of vitality, and alteration of the shape of the thallus.
e) Reduction of photosynthesis and respiration
f) Reduction of fertility.
The reaction of lichens to air pollution and their decay can occur in very short time.