A decomposer is an organism that breaks down dead plant or animal matter. This may arouse the yuk response in many readers, but the fact is that ecosystems could not function without decomposers. This is because ecosystems depend on recycling in order to function. Humans are used to throwing away things they don’t want, but in nature, all materials are recycled endlessly.
Dead bodies contain many useful substances that are often in short supply in ecosystems: carbon tied up in large carbohydrate molecules, calcium and other minerals, organic nitrogen bound up in proteins. Without the help of decomposers, these elements would be removed from the food chain and gradually become so rare that the ecosystem would cease to function.
Carbon, hydrogen, oxygen, nitrogen and the other necessary elements of life are all recycled. The oxygen we breathe in today was once breathed in by dinosaurs. The carbon dioxide that we breathe out is used by plants to create sugars in the process of photosynthesis. When animals eat plants, those simple sugars and carbohydrates are broken down and used as the building blocks for animal fats, carbohydrates and proteins.
When plants and animals die, those large complex compounds cannot be directly used again. Instead the decomposers break them down and make them available. So what are these decomposers? Bacteria and fungi do the majority of decomposition work. Worms and maggots also help. Fungi work mainly on plant materials, breaking down even cellulose and lignin, the largest of the complex carbohydrates. Bacteria work on everything from animal proteins to plant carbohydrates. Once these are broken down into smaller molecules, they can be ingested by small animals such as insects or taken up by plant roots and thus made part of the food chain again.
Nitrogen is an interesting element. It is present in the air we breathe as N2 but this is not a form that animals can use directly. Yet we need nitrogen to make proteins, the building blocks of our bodies. So where can we get it from? We can recycle organic nitrogen by eating meat but only nitrogen fixing bacteria can provide new sources of nitrogen from the air. Without bacteria to break down the proteins in dead bodies and fixing the nitrogen in the air, animals could not get enough nitrogen to make the proteins necessary for them to grow and function.
So next time you walk through a forest, think of the tiny but necessary organisms beneath your feet. Without their constant work to recycle the dead, the living ecosystem around you could not function or continue to exist. All life depends on the decomposers just as they depend on us.