What is the key environmental role of lichens?

Lichens play a crucial environmental role as indicators of air quality. This is due to their sensitivity to pollutants, particularly sulfur dioxide and heavy metals. They absorb moisture and nutrients directly from the air, which makes them especially vulnerable to environmental changes. If the air quality declines, many lichen species will react negatively, often demonstrating reduced growth or even dying off. This sensitivity allows researchers and environmentalists to use lichens as bioindicators to assess the health of air ecosystems and detect pollution levels.

The other options do not accurately reflect the primary role of lichens in the environment. While decomposers and primary producers serve essential functions in various ecosystems, lichens primarily perform their unique role as indicators. Also, lichens are not invasive species; they typically contribute to the ecosystem by enhancing biodiversity and promoting nutrient cycling rather than disrupting existing habitats.