Ecological Roles of Lichens as Monitors of a Changing Global Environment

Lichens represent a fundamental symbiotic association between fungi and photosynthetic organisms, such as algae or cyanobacteria, and are widely regarded as sensitive indicators of environmental change. Lichens' capacity to colonize a wide range of ecological niches is attributed to their distinctive physiological characteristics, notably, their lack of protective cuticles and ability to uptake water and nutrients directly from the atmosphere. Concurrently, lichens are highly vulnerable to airborne contaminants, making them critical bioindicators of air quality. However, the survival of lichens is increasingly influenced by intensifying global change via agriculture, industrial activities, and vehicular emissions. Organic and inorganic pollutants can adversely affect lichen physiology by inducing pigment degradation, disrupting membranes, and altering lichen diversity. The synergistic stressors associated with global change, such as increasing temperatures and shifts in precipitation regimes, exacerbate the effects of atmospheric deposition and oxidative stress on lichens. Here, we present existing knowledge on lichens' ecological functions, elucidate the mechanisms underlying their sensitivity to air pollution, and assess their utility for environmental monitoring amid accelerating global change. By recognizing lichens as dynamic ecological indicators, we underscore their dual role in sustaining ecosystem processes amidst rapid global change.