# Ecological Roles of Lichens as Monitors of a Changing Global Environment

## TL;DR

Lichens are sensitive to pollution and environmental changes, making them useful as natural indicators of environmental health.

## Contribution

The paper highlights lichens' dual role as ecological indicators and contributors to ecosystem processes under global change.

## Key findings

- Lichens act as early warning systems for environmental degradation due to their sensitivity to pollution.
- Pollutants damage lichen pigments and cellular structures, reducing their diversity and abundance.
- Global change stressors like temperature and precipitation shifts worsen lichen vulnerability to pollution.

## Abstract

Lichens are complex, self-contained ecosystems formed by the symbiotic relationship between fungi and photosynthetic organisms, such as algae or cyanobacteria, which can signal when the environment is changing or becoming polluted. Because they lack a protective skin layer, they can absorb water directly from the air or soil. While this helps them live almost everywhere, it also makes them extremely sensitive to pollution. For this reason, we review how lichens act as biological indicators, or “bioindicators,” of environmental quality. Today, pollution from farming, factories, and cars is threatening their survival. These pollutants damage lichens by destroying their pigments (turning them white) and breaking down their cellular structures. The problem is worsening due to rising temperatures, changing rainfall patterns, and pollution. Our study found that lichens act as an early warning system: when they start to disappear or their abundance and diversity decline, it signals that the environment is becoming too toxic for their survival, growth, and activities.

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.