What trophic levels do decomposers feed on?

They are the “last trophic level” in some hierarchies because they feed on everything (National Geographic).

However, according to the strict trophic level definition they would be primary consumers.

They are the “last trophic level” in some hierarchies because they feed on everything (National Geographic). However, according to the strict trophic level definition they would be primary consumers because they consume a source “produced” by natural cycles like plants.

Unless the organism actually invades, attacks, or otherwise causes the death of another trophic level source, it cannot really be considered to consume that form. It is consuming something different than the original creature. See the following diagram.

See also the following helpful sites:

http://www.eschooltoday.com/ecosystems/ecosystem-trophic-levels.html