Why Are Lichens A Good Pioneer Species After A Volcanic Eruption?

Lichens are pioneers of Species, they have the ability to settle on substrates that are very low in nutrients and can withstand extreme temperatures and light conditions.

The bare rock surfaces formed after a volcanic eruption lack soil and are exposed to harsh weather conditions. In this litho sere, the change is occurring via primary succession, meaning that there has been no previous decomposition of plant material, and so there are no nutrients in the rock.

There is no soil to retain water and the rock surface would most likely be exposed to the sun meaning that any moisture to settle there would quickly evaporate.

A dry rock surface also reflects and absorbs heat, which could result in the temperature becoming too high for any but the most resilient pioneer species to colonies there.

Lichens (the pioneer species) are able to survive because they are specialized to cope with hostile abiotic conditions. Lichens can grow in cracks to avoid the wind and they secrete acids that erode rock to release minerals.

Why Are Lichens A Good Pioneer Species After A Volcanic Eruption?

The pioneer species have now changed the abiotic conditions. As they die and decompose the lichens help form a thin soil, which thickens as more organic material is formed. This allows other species, such as mosses, to grow.

The basic soil helps to retain more water, allowing larger plants to colonize the area as the soil deepens (e.g. grasses and small flowering plants). The soil continues to become deeper and richer in nutrients as the larger plants die and are decomposed.

In the new, no longer hostile conditions, shrubs, ferns, and small trees begin to grow. They are better adapted to the new environment and so can out-compete the grasses and smaller plants for space and nutrients.

In the final sere, the soil is rich and deep enough in nutrients to support large trees. These become the dominant species, and the climax community is formed.

How do lichens colonize new substrates?

Through their ability to adapt to living in extreme conditions, lichens can colonize substrates that are low in nutrients and are considered true pioneers.

The dispersal of spores formed by lichen is one of the first steps in colonization (see Focus Lichens: hybrid organisms). Indeed, once mature, the lichen spores are violently ejected outside the asci and fall on the substrate.

They germinate by emitting mycelial filaments that branch quickly. For a lichen to recover, the mycelium thus formed must meet an algae partner.

Recognition is most often carried out using molecules such as lectins that impregnate the cell walls. A young undifferentiated thallus is then formed, which gradually acquires the adult form and, most of the time forms reproductive organs.

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