What trophic levels do decomposers feed on?

The exact number of biomes depends on who you ask.
The exact number of depends on who you ask. Different people and/or organizations classify biomes in slightly different ways. Some will say that there are five, some , and some more.
It is common to state that there are five major biomes: deserts, aquatic, forests, grasslands, and tundra. Read more about them here.
NASA lists seven biomes: tundra, shrubland, rainforest, grassland, desert, temperate deciduous forest, and coniferous forests.
Others may say there are nine biomes: marine, freshwater, savanna, grassland, taiga, tundra, desert, temperate forest, and tropical rainforest.
More examples of biome classifications are below.
To conclude, the number of biomes depends on who is classifying them and the number of biomes depends on this.
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: