Project Amazonia: Characterization - Biotic - Algae/Fungi

Algae

Algae are unicellular or multi-cellular phototrophic microorganisms that need light to flourish and live in aquatic environments. They can exist as single cells, filaments, colonies and multi-cellular forms. Sugars synthesized with the help of the two types of chlorophyll are the main energy source for the algae, which uses them to grow and reproduce. The most common group is known as Green Algae (Chlorophyta).

Red Algae (Rhodphyta) and Brown Algae (Phaeophyta) also exist.  They are multi-cellular, with cells that can be quite different from one another and have different functions.  Some types can grow quite large.  Bladderwrack and kelp seaweed, for instance, are types of brown algae.  Bacterial green algae also exist, including certain members of the chromista, rhodophyta, and photosynthetic bacterial groups¹.  Another bacterial group is classified as blue-green algae, but this group belongs to the cyanobacteria because it lacks a nucleus in the cell.

Fungi

Fungi are very resistant to changes in the environment and are highly adaptive. They can survive environmental conditions that most other eukaryote life-forms could not withstand. Their method of propagation utilizes spores, which spread widely and are relatively unselective in where they root. The body, called mycelium, of fungi is made of threads called hyphae, which absorb nutrients from the substrate, spread, grow, and produce fruiting bodies. These bodies are the visible parts of the fungus. Fungi are unable to produce their own food, so they obtain nutrients from dead organic matter or living organisms. The functions of fungi are highly diverse and have many implications for science and the health of the rainforest.

There are three types of symbiosis: parasitic, mutual, and neutral. Parasitic relationships benefit the fungus, but harm the host. This type of relationship is often observed as a problem for agriculture. Neutral relationships benefit the fungi without harming the host

A mutual relationship is beneficial for both the fungus and the host. Two types of Mycorrhizal mutual symbioses are seen in the soil of the Amazon: ectomycorrhizae and endomycorrhizae. Both are methods of aiding plant ion absorption, the difference being ectomycorrhizal fungi only coat the root system, while endomycorrhizal fungi invade the primary cortex of the root system, though still leaving the main roots and secondary cortex intact. This symbiotic relationship effectively increases the active surface area of the plant roots by as much as a factor of ten. These fungi supply the plants with P, N, and K in a usable form, as well as limit pathogen entry through the roots. This results in increased water regulation, allowing for a more rapid recovery from droughts and a biotic stresses. In exchange, these plants provide the fungi with sugars produced through photosynthesis.

A recent study done in Venezuela suggests that mycorrhizae inoculation could be used to aid in rehabilitation of deforested soils. The experimenters attempted two methods of treatments (as well as controls). One involved phosphorus fertilizers and mycorrhizal inoculation (I+P), while the other was only inoculation with mycorrhizal fungi (I). The (I+P) treatment caused a 60% increase in above ground biomass after a five month re-growth period as compared to a control, and twenty times that of the (I) treatment. The chemical analysis of these soils showed that while no exchangeable P was detected in the controls, there was about 2.17 mg/g in inoculated and fertilized soils. The researchers believe that this is because in general, plants in mature tropical ecosystems depend on presence of mycorrhizae for their development. Therefore, when disturbance, such as deforestation, causes a loss of mycorrhizae, "recovery of the degraded areas is only possible if these propagules are reintroduced by natural processes or human intervention"².

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