Decomposers

The cycling of materials such as carbon, water, and other nutrients is mainly dependent upon soil-dwelling decomposer organisms such as bacteria fungi, earthworms, and insects. Bacteria and fungi are the most abundant of the microbial decomposers, numbering in the billions in only one handful of soil!

        As essential components of the environment, fungal and bacterial microbes break down dead and discarded organic materials, supplying a continuous source of nutrients for the plants in surrounding soil. In general, decomposers break down the proteins, starches, and other complex organic molecules that were all once the components of living organisms, and “as products of their own metabolism, [they] convert elements such as nitrogen, phosphorous, calcium, and sulfur into forms that can be utilized by plants” (Dirty, 2). According to several researchers at the University of Jyväskylä, "Reduction in the species diversity of the lowest levels (decomposer fungi) of the food web [become] particularly well manifested as reduced decomposition rate and stagnated nutrient dynamics." They also emphasized that certain variations of microorganisms can play a critical role in controlling nitrogen cycles and plant growth in general.

In addition, it is true that decomposer species tend to be rather resistent to changes in the availablitiy of organic material or changes to the environment in general, but they are still affected by several key factors. For instance, increases in temperature will cause more rapid decomposition reactions--just as would occur for most chemical reactions. However, too high of an increase in temperature affects the microbes adversely. Moisture is also usually favorable unless there is so much moisture that the living environment is waterlogged. When waterlogging occurs, some microbes will die while others thrive on the excess moisture.  On the other hand, light tends to be bad for most decomposer microbes.

Concerning the issue of oil drilling on the North Slope of ANWR, one would expect an increase in the amount of organic as well as inorganic waste material in the local environment. This is important, because although fungi and microorganisms thrive off of organic materials such as animal flesh, fecies, dead plant matter, nut shells, etc.,  it is much harder and time consuming for them to decompose human-made materials that are either high in cellulose--i.e. cotton and paper-cardboard--or metallic or plastic. In fact, metals and plastics are almost impossible to decompose by the microorganisms and fungi--they break down primarily, and over a long period of time, due to weathering processes. Currently advances are being made in the development of biodegradable plastics, but there remains the majority of non-biodegradable plastics. Furthermore, if the diversity of decomposer species decreases in ANWR due to changes in their environment--whether the changes are related to climate, the introduction of oil drilling, or increases/decreases in populations of consumers--it can be assumed that all species that depend upon the decomposers are either directly or indirectly affected by such a flux.

Species:

Although it is true that “no one has yet detailed all the species of fungi that live in Alaska” and “several thousand species of fungi exist, but scientists have only described about 50,000,” much can be said about the characteristics and effectiveness of these incredible decomposers. (http://www.gi.alaska.edu/ScienceForum/ASF15/1562.html)

According to the book Ecology of Arctic Environments, research has shown that frost free days and varying levels of nitrogen in soil are not greatly important to the survival of fungi, while temperature, moisture and pH are. In addition, it appears that the cold of the arctic may “have a selective effect” on certain species such as Chrysosporium  pannorum. As for arctic fungal species in general, several studies have illustrated that “fungal h yphal length increased with increasing soil moisture and temperature, and decreasing soil pH” (Woodin and Marquiss).

Unfortunately for our purposes, the fungal species lists and biomass values that are available are almost all composed from the research efforts of the Tundra Biome group of the IBP, and are therefore from the long ago period of 1964-1974. Species known to have been studied by the Tundra Biome group include Eriophorum and Carex (Woodin and Marquiss).

General Characteristics:

Suffice to say, “fungi, the subjects in this kingdom, live in the woods, in refrigerators, on rocks, and between our toes. Without them, the natural world would cease to function.”

Fungi are part of a very interesting kingdom. In fact, it is so diverse and complex that they are the only species that make up the kingdom. To function on a regular basis, fungi digest their food through the use of extracellular fluids. In other words, digestion occurs outside of their bodies. The extracellular fluids that they excrete are acids and enzymes that act to break down organic material. They then absorb the simple molecules of food through their cell walls, because they do not have stomachs.

Furthermore, many fungal species exist in symbiotic relationships with vegetation such as trees. An example of such a relationship occurs when fungi beneath the soil cling on to tree roots, resulting in roots that are coated with hairy fungi called mycorrhizae. The fungi help trees and other plants absorb minerals (http://www.gi.alaska.edu/ScienceForum/ASF15/1562.html).

Furthermore, “decomposer microorganisms require a balance of carbon and nitrogen that requires a far greater turnover of nitrogen accompanying carbon dioxide production…in order to simultaneously meet energetic and nutritional needs” (Reynolds et. al, 311). Plants even compete both with each other and with soil microbiota for the nitrogen and nutrients released through decomposition. Therefore, when the availability of nitrogen is lower, it is harder for a variety of plants to survive.

Investigations on decomposition in the arctic have been conducted primarily by Flanagan and Scarborough as part of the Tundra Biome project that occurred from 1964-74. They stated that the best soil pH for cellulose decomposition by about 60% of Alaskan strains was between 4.5 and 5 (acidic), while a slightly more basic pH of 6 was best for the decomposition of pectin and starches (Woodin and Marquiss).

It is observed that the “fungal species composition in arctic environments is very similar to those in temperate latitudes, although the isolates are often adapted to low temperatures” (Woodin and Marquiss). Nevertheless, in the extreme soils that are more characteristic of the North Slope (aka the 1002 region—that which is in debate for oil drilling), fungal biomass is clearly seasonal and may overall be lower than that which is found in temperate ecosystems.

At the University of Alaska Fairbanks, the Institute of Arctic Biology scientists are attempting to determine the “characteristics of tundra and forest fungi that allow them to live in cold soils and to release nitrogen and phosphorus as they decompose organic remains.”  The resistance of fungi to oil spills or other environmental disturbances must be investigated and known, for “if the stability of the fungi is undermined, an entire forest or tundra grazing land can be destroyed.