Introduction to Lichens

Introduction to Lichens

• Lichens are symbiotic organisms, a combination of a fungus (mycobiont) and a photosynthetic partner (photobiont).
• The photobiont is usually an alga (e.g., green alga, cyanobacterium), but sometimes a non-photosynthetic bacteria (e.g., mycoplasma).
• The fungus provides a supportive structure and environment for the photobiont.
• The photobiont provides the photosynthetic products necessary for survival and growth of the lichen symbiosis.
• This unique partnership allows lichens to colonize diverse habitats, from harsh Arctic environments to tropical rainforests.

Structure and Morphology

• Lichens exhibit diverse morphology, often falling into three main types:
  • Crustose lichens: These are tightly attached to their substrate, appearing as a crust.
  • Foliose lichens: These characteristically have leaf-like or lobed structures.
  • Fruticose lichens: These lichens exhibit a shrub-like or branched morphology.
• The thallus (body) of a lichen is composed of fungal hyphae, which form a network that protects and encapsulates the photobiont cells.
• Specialized structures called apothecia are often present, and can be seen as cup-shaped or saucer-like, containing reproductive structures (ascospores) produced by asexual reproduction.
• The presence of these apothecia allows for the reproduction of the lichen.

Habitats and Distribution

• Lichens are extremely widely distributed around the world, establishing themselves in many different environments.
• They are quite adaptable to varied conditions, though they generally do not thrive in polluted or harsh environments.
• Lichens often colonize bare rocks, tree barks, and soil surfaces, especially in locations with reduced plant life.
• Their ability to withstand harsh conditions makes them important pioneers in primary succession.

Importance and Role in Ecosystems

• Lichens are crucial components of many ecosystems, acting as:
  • Bioindicators of air quality: Their sensitivity allows researchers to assess the quality of the air through the lichen species present or absent.
  • Producers in food webs: Certain lichen species serve as a direct source of food for herbivores.
  • Soil formation: Lichens contribute to the physical breakdown of rock surfaces, aiding in soil formation.
• Lichens play a key role in nutrient cycling and nutrient uptake.

Reproduction

• Lichens reproduce both asexually and sexually.
• Asexual reproduction occurs via fragmentation of the thallus, producing new individuals.
• Sexual reproduction typically involves the formation of apothecia, which release ascospores.
• The ascospores, on landing in appropriate conditions, germinate and develop into new lichen thalli.

Threats and Conservation

• While lichen populations are relatively resilient, certain threats can affect these important organisms:
  • Air pollution: Exposure to pollutants can negatively impact lichen health and diversity.
  • Habitat destruction: The loss or degradation of lichen habitats reduces their population.
  • Climate change: The changing climate conditions have a potential impact on lichen distribution, diversity, and survival.
• Conservation efforts focus on reducing environmental stresses, protecting lichen habitats, and promoting sustainable practices that minimize lichen harm.

Lichen Diversity and Study

• The world's lichen diversity is vast and complex.
• Many different species exist, and studying them plays a crucial role in:
  • Ecosystem monitoring: Detecting changes in air quality and habitat conditions.
  • Understanding symbiosis: Investigating the complex relationships between fungal and photosynthetic partners.
  • Developing novel research techniques for studying the lichen microbiome, or examining the genetic information of lichens.