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Once filaments have stabilized the soil, lichens and mosses can colonize. Appressed lichens are generally earlier colonizers or persist in more stressful conditions, while more three-dimensional lichens require long disturbance-free growth periods and more moderate conditions. Recovery following disturbance varies.
Lichen is able to absorb nitrogen in multiple forms from soil, rock, and air, taking a part in carbon cycle at the same time. Even though only a small fraction of lichens have the ability to fix nitrogen, it helps the lichen to spread throughout the world and survive even in the harsh environment.
Crustose lichens differ from the leprose lichen by having an upper cortex and algal cells that are located directly beneath the cortex. The thallus of a crustose lichen has a patchwork or crazy-paving appearance. The patches, or areolae, can be as large as 1 cm in diameter or very small and raised, giving them the appearance of a wart.
Evidence that lichens are examples of successful symbiosis is the fact that lichens can be found in almost every habitat and geographic area on the planet. [20] Two species in two genera of green algae are found in over 35% of all lichens, but can only rarely be found living on their own outside of a lichen. [51]
Some lichens grow on rocks without soil, so may be among the first of life forms, and break down the rocks into soil for plants. [11] Since some uninhabited land may have thin, poor quality soils with few nutrients, pioneer species are often hardy plants with adaptations such as long roots, root nodes containing nitrogen-fixing bacteria, and leaves that employ transpiration.
When major geological changes such as volcano eruptions or landslides occur, the current vegetation and soil may erode away leaving only rock. Primary succession occurs when pioneer species such as lichens colonize rock. As the lichens and mosses decompose, a soil substrate forms called peat. The peat, over time, will create a terrestrial ...
One fungus, for example, can form lichens with a variety of different algae. The thalli produced by a given fungal symbiont with its differing partners will be similar, and the secondary metabolites identical, indicating that the fungus has the dominant role in determining the morphology of the lichen.
Lichenicolous lichens are relatively common; a study in Italy found that 189 of 3005 lichenised species (about 6%) were lichenicolous. [19] These lichens show distinct biological and ecological characteristics. They are predominantly crustose, mostly have green, non-trentepohlioid algae as photobionts, and primarily reproduce sexually.