Fungi belong to Kingdom Mycota, a group of eukaryotic organisms whose digestive enzymes are released to act on food externally. After external digestion, the organism obtains the nutrients through absoprtion. In most fungi, reproduction is through spores (Deacon, 2006). A major characteristic of fungi is that they have a body called thallus with a number of microscopic tubules or cells known as the hyphae (Deacon, 2006). Like animals, they must depend on other organisms to obtain carbon and energy (Blackwell, 2011).
Despite this, most other living organisms depend on fungi for their survival. In most cases, fungi form mutualistic relationships with plants, animals or bacteria. In these relationships, both organisms depend on each other for survival. Nevertheless, it appears that bacteria, plants and animals depend more on fungi than fungi depend on them.
First, the relationship between plants and fungi shows that plants depend more on fungi than fungi depend on them. In fact, it also explains how animals, which depend on plants for survival, have an indirect but important dependency on fungi.
Mycorrhiza, a term derived from the Greek words “myco” to for “fungus” and “rhizo” for “roots”, is scientifically used in reference to the association between fungi and the symbiotic vascular plant roots (Sorensen, Larsen & Jakobsen, 2005). Studies have shown that over 90% of all plant species on earth depend on some fungi (Deacon, 2006). These fungi are their mycorrhizal partners. In the association, the mycelia of the fungi use the extensive hyphal networks as well as the large surface area exposed to the natural soil to obtain both water and minerals (Rillig, 2004). The plant partner obtains these important compounds from the fungi, which increases their nutrient uptake. On the other hand, the plant has an extensive photosynthetic system that the fungi lack. As such, the plants supply the photosynthetic products from its photosynthetic parts to the fungus.
Considering that more than 90% of all plant species on earth cannot live without minerals and nutrients obtained from the fungi, it is important to consider the role that fungi play in the ecosystem. This implies that more than 90% species cannot survive if the kingdom fungi cease to exist (Rillig, 2004). It is also important to note that all animals have varying degrees of dependency on plants. Plants form the chief source of nutrients for animals. The ecology of animals and plants indicate that more than 70% of plants directly support the life of animals, whether directly or indirectly. This implies that animals indirectly depend on fungi (Grant, Bitman, Montreal, Plenchette & Morel, 2005).
A mutual relationship between animals and fungi reveal that animals also have a direct dependency on fungi. In particular, fungi have a direct relationship with a number of insects. For instance, arthropods depend on fungi for their protection from pathogens as well as predators. A symbiotic relationship exists between insects and the fungi of the species Basidiomycota. In this relationship, scale insects obtain nutrients from fungal infect plants. Insects cut plant leaves and pile them on the ground to attract fungi. Then, fungi infect the disks and digest cellulose in them (Boerjan, Ralph & Baucher, 2003). The insects than consume cellulose molecules as their source of energy. This phenomenon is common in South and Latin America.
In the nutrient cycle, fungi play a crucial role of transporting, storing, releasing and recycling nutrients in the ecosystem, which supports the lives of other species (Boerjan, Ralph & Baucher, 2003). The concept of nutrient cycle refers to a sustainable phenomenon that ensures a continuous absorption, use and release of carbon-based and nitrogen-based compounds and minerals. Almost all the organisms actively contributing to the nutrient cycle are the fungi, bacteria and plants. In this case, fungi are the agents of decomposition of plant components. In particular, cellulose and the lignin are released. In this way, the decomposing plant parts give out the nutrients make them available for other organisms (BĂĽcking & Shachar-Hill, 2005).
In acidic soils, fungi play an important role in making it possible for plants to survive in highly acidic environments. In this case, bacteria cannot survive in extremely low pH. However, fungi survive in these conditions. Therefore, plants must depend on fungi as the chief agents of decomposing where bacterial cells are lacking. Fungi decompose matter and derive nitrogen, carbon and minerals needed for the survival of the plants (BĂĽcking & Shachar-Hill, 2005).
Though not well understood, the endophytic relationships between plants and fungi are an important phenomenon that indicates high degree of plant dependency on fungi. In this case, studies have shown that a number of fungal species reside inside plants as inconspicuous embroidery of filaments. Recent studies indicate that most plants have incorporated fungi within their tissues (BĂĽcking & Shachar-Hill, 2005). Studies have shown that the existence of fungi inside plants is an evolutionary phenomenon that has made it possible for plants to survive through effective systems of nutrient cycles within them. The internal nutrient cycle is accomplished through the endophytic fungi that have been incorporated within the plant body during their evolution (BĂĽcking & Shachar-Hill, 2005).
Fungi also play an important role in the regulation of populations on earth. As microbes, fungi cause diseases, death and decomposition (Blackwell, et al., 2006). To check the population of plants and animals, fungi must cause plant and animal diseases to eliminate some individuals and maintain the right population per given time and space (BĂĽcking & Shachar-Hill, 2005). For instance, the decline in bat populations in the US is associated with the Geomycetes destructans, a fungal species that causes the white-nose syndrome in bats. Mycoses are animal-infecting fungi that cause diseases in humans and other animals in an attempt to control population (Blackwell, et al., 2006). For example, the Pneumycostic carinii, a fungus that emerged as the chief cause of deaths among the HIV/AIDS patients, played a significant role in reducing populations, a factor that could be used to explain the fungal role in population control.
References
Blackwell, M. (2011). The Fungi: 1, 2, 3…5.1 million species? American Journal of Botany 98, 426-438.
Blackwell, M., Hibbett, D.S., Taylor, J.W., & Spatafora, J.W. (2006). Research Coordination Networks: a phylogeny for kingdom Fungi (Deep Hypha). Mycologia 98, 829-837.
Boerjan, W., Ralph, J., & Baucher, M. (2003). Lignin biosynthesis. Annual Review of Plant Biology 54, 519-546.
Bücking, H., & Shachar-Hill, Y. (2005). Phosphate uptake, transport and transfer by arbuscular mycorrhizal fungus is increased by carbohydrate availability. New Phytologist 165(3), 889–912
Deacon, J. (2006). Fungal Biology. Malden, MA: Blackwell Publishing.
Grant, C., Bitman, S., Montreal, M., Plenchette, C., & Morel, C. (2005). Soil and fertilizer phosphorus: effects on plant supply and mycorrhizal development. Canadian Journal of Plant Science 85, 3–14.
Rillig, M. (2004). Arbuscular mycorrhizae, glomalin and soil aggregation. Canadian Journal of Soil Science 84(4), 355–363.
Sorensen, J.N., Larsen, J., & Jakobsen, I. (2005). Mycorrhizae formation and nutrient concentration in leeks (Allium porrum) in relation to previous crop and cover crop management on high P soils. Plant and Soil 273, 101–11.