Lichen and Bryophyte Study Notes
Overview of Lichens
- Lichens are unique symbiotic organisms composed of:
- Fungi
- Algae or Cyanobacteria (or both)
- The relationship allows for mutual benefits:
- Algae/Cyanobacteria
- Capable of photosynthesis.
- Produce sugars when exposed to sunlight.
- Fungi
- Provide physical protection for algae and cyanobacteria.
- Mineralize rocks to supply essential minerals to algae and cyanobacteria.
Discovery of Yeast in Lichens
- Recent studies, notably by Purdue University, revealed the presence of yeast in lichens.
- Yeast are unicellular fungi, different from filamentous fungi.
- This finding is essential for:
- Understanding variability in physical features of lichens despite genetic similarity.
- Explaining the difficulty in synthesizing lichens in laboratory conditions.
- Importance of ongoing microbial life studies to uncover hidden aspects of biodiversity in lichens.
Genera Associated with Lichens
- Primarily, lichens consist of three genera of algae:
- Trabuxia
- Pseudotrabuxia
- Tranthropolia
- For cyanobacteria, a notable genus is:
- Approximately 90% of lichens include these four genera, typically associated with Ascomycete fungi.
- Some lahens may also relate to:
- Ascomycetes are currently the most documented with over 13,000 species named.
Lichen Morphology and Classification
- Lichens can be classified by their visual morphology into three main types:
- Crustose:
- Low-growing, crusty, and tightly adhered to substrates.
- Appear crumbly and flat.
- Foliose:
- Leaf-like structure, more open than crustose, but still relatively low to the substrate.
- Fruticose:
- Upright, bush-like growth.
- The body of the lichen is often referred to as a thallus.
Growth and Reproduction of Lichens
- Lichens grow slowly, colonizing harsh environments and can help establish soil.
- Sorevia: Fragmented hyphae that allow lichens to disperse when dislodged by rain or animals.
- Lichens are primary colonizers, often the first life forms post-disturbance (e.g., after a fire).
- Some cyanobacterial partnerships assist in nitrogen fixation, making nitrogen accessible for other organisms.
Environmental Tolerance and Vulnerability
- Lichens can withstand extreme environments but are sensitive to air pollution.
- Pollution can affect their chlorophyll and overall health leading to declines in lichen populations.
- A study indicated that lichen abundance decreases with proximity to city centers, with significant declines observed up to 30 kilometers from urban areas.
Student Studies on Lichens
- Student presentations, such as one by Kathleen, demonstrated increase in lichen population density away from urban areas, especially on tree trunks.
- Notable lichen types included variability based on their habitat, notably tree sides (north vs. south).
Ecological Roles of Lichens
- Lichens contribute to nutrient cycling by:
- Introducing minerals to rocky substrates.
- Fixing nitrogen in ecosystems where nitrogen is limiting, assisting plants and other organisms.
- Certain lichen species can tolerate dehydration and rehydrate to resume metabolic activity after moisture returns.
Transition from Lichens to Bryophytes
- Bryophytes, including mosses, liverworts, and hornworts, represent the next step in plant evolution after lichens.
- These plants are characterized by:
- Dependence on moist habitats for reproduction (motile sperm).
- Lack of true vascular tissues, roots, and reliance on whole body for water absorption.
- Phylum classifications include:
- Bryophyta (mosses)
- Anthocerophyta (hornworts)
- Hepatophyta (liverworts)
Key Concepts: Alternation of Generations
- In bryophytes, life cycle includes two distinct phases:
- Haploid (N) phase (Gametophyte): Dominant phase where gametes are produced (egg and sperm).
- Diploid (2N) phase (Sporophyte): Follows fertilization of zygote, resulting in growth through mitosis.
- Understanding transitions between these phases is crucial for grasping plant reproductive strategies.