Oct 7 • Compost and Microbial Activity
Different Members, Different Jobs
Last time we looked at a compost pile as a living community rather than simply a heap of material breaking down, but it is important to note that not every member of that community is doing the same job. Some organisms work directly on the organic material itself. Bacteria and fungi are important primary decomposers at different successions although their relative activity can change as conditions and available food change within the pile. Each use compounds in leaves, grass, kitchen scraps, stems, manure, and other organic materials as food and energy although many times in different ways.
Actinomycetes also contribute to decomposition. Despite the name, they are actually filament-forming bacteria. They are often associated with breaking down some of the tougher materials that remain as decomposition continues. But decomposition is not only about organisms processing dead plant material. There are other members of the community that interact with the organisms doing that work.
Protozoa and some nematodes graze on microorganisms. Arthropods can shred and fragment larger pieces of material. By making pieces smaller, they can expose more surface for microorganisms to work on. Worms, when conditions suit them, consume decomposing organic material along with the microorganisms living on and around it. As they move through the material, they also help mix and change the habitat.
These roles are not perfectly separated. An organism may influence the pile in more than one way, and several kinds of organisms may be active at the same time. That is why I think it is more useful to picture compost as a working community than as a list of individual creatures. Some members are breaking materials down chemically, while others are grazing or shredding larger pieces. Some creatures simply move and mix the material. Each of those activities can change the habitat for someone else.
The important principle is that the decomposer community works through different but overlapping roles. This also helps explain why seeing one organism does not tell us everything happening in the pile. Finding worms may tell us that the conditions where they are living are suitable for them, but it does not mean worms are doing all the decomposition. Seeing fungal growth as a pile cools or cures does not mean bacteria are absent. Each can remain part of the community balancing each other even as their relative activity changes.
Not seeing insects does not mean nothing is happening either. Much of the work in compost is happening beyond what we can easily see. This week, if you have access to a compost pile, leaf pile, mulch layer, or worm bin, take a few minutes to look closely. Can you find evidence of more than one kind of work happening? Look for material softening, fungal growth, smaller pieces created by shredding, tunnels or movement through the material, or organisms feeding within it. We are not trying to identify all the organisms, we are simply noticing that decomposition is being carried forward by a community whose members contribute in different ways.
Which statement best describes how the decomposer community works in a compost pile?
Every organism performs essentially the same job.
Bacteria and fungi do the decomposition while larger organisms have little effect.
Different organisms contribute in different ways, and their activities can overlap.
Each group finishes its work before the next group begins.
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Different Members, Different Jobs
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