Lichens and Environmental Health

Lichens: Ecological Importance and Indicators of Environmental Health

• Soil Formation and Stabilization: Lichens are pioneer organisms, initiating soil formation by breaking down rock surfaces with secreted acids. Examples include Rhizocarpon geographicum in alpine and arctic regions.
• Nutrient Cycling: Lichens fix nitrogen (some species) and decompose organic matter, enriching soil nutrients. Peltigera canina, for instance, forms symbiotic relationships with nitrogen-fixing cyanobacteria, boosting nitrogen in forest soil.
• Habitat and Food Source: Lichens provide habitats and food for various organisms (insects, birds, mammals). Cladonia rangiferina (reindeer lichen) is a crucial winter food source for reindeer and caribou.
• Air Quality Indicators: Lichens are sensitive to air pollution (especially sulfur dioxide). Their presence/absence indicates pollution levels. Lecanora conizaeoides thrives in polluted environments, indicating high pollution.
• Ecosystem Monitoring: Lichen diversity and health reflect environmental changes. Lichen surveys monitor impacts of climate change and pollution. Xanthoria parietina is studied for symbiosis and stress tolerance.
• Climate Change Studies: Lichens' sensitivity to environmental changes is used to study the impacts of climate change, understanding ecological responses. Polar regions (Cladonia arbuscula) exemplify this use in climate change analysis.
• Cultural and Historical Significance: Lichens have traditional uses in cultures – medicine, dyes, food. Cetraria islandica (Iceland moss) has traditional uses in Icelandic medicine and cuisine.

Orchid Mycorrhizae

• Description: Orchid mycorrhizal fungi are crucial for orchid seed germination and early development. Orchid seeds lack sufficient reserves.
• Structure: Hyphal structures (pelotons) form within orchid root cells.
• Hosts: Orchidaceae family (orchids).
• Examples: Rhizoctonia spp. and Ceratobasidium cornigerum form mycorrhizal associations with various orchid species.

Arbutoid Mycorrhizae

• Description: Similar to ectomycorrhizae, specifically associated with plant families like Ericaceae. They form a dense hyphal sheath around roots and penetrate root cells.
• Structure: Dense fungal sheath (hyphal sheath) surrounds root tips and intracellular hyphae form coils or pelotons within root cells.
• Hosts: Plants like Arbutus and Arctostaphylos.
• Examples: Arbutus menziesii (Pacific madrone) and Arctostaphylos uva-ursi (Bearberry) form arbutoid mycorrhizal associations.

Applications in Agriculture

• Sustainable Agriculture: Mycorrhizae reduce the need for chemical fertilizers and pesticides. Inoculating crops with arbuscular mycorrhizal fungi (e.g. in maize) demonstrates this.
• Horticulture: Mycorrhizal inoculants enhance the growth and health of ornamental plants, trees, and shrubs (e.g. roses).
• Forestry: Mycorrhizae aid in tree establishment and growth, important for reforestation and afforestation (e.g. ectomycorrhizal fungi in reforestation projects).
• Crop Production: Mycorrhizal fungi enhance crop growth and yield (e.g. wheat with arbuscular mycorrhizal fungi).