There isn't a single perfect antonym for "biome" as it's a broad term. However, depending on the context, you could consider these alternatives:

If you're focusing on the scale:

* Microhabitat: This refers to a very small, localized habitat within a larger biome.

* Niche: This refers to the specific role an organism plays within an ecosystem.

If you're focusing on the diversity of life:

* Monoculture: This refers to a single species of plant being grown over a large area.

* Sterile environment: This refers to an environment devoid of life.

If you're focusing on the natural vs. artificial:

* Artificial environment: This refers to an environment created by humans, like a city or a farm.

Ultimately, the best antonym for "biome" will depend on the specific situation.