G. Decomposing bacteria break down dead organisms and return nutrients to the soil.
Explanation:
Bacteria break down dead matter in the environment, for example, dead leaves, and release carbon dioxide and nutrients in the process. Without the release of carbon dioxide, plants are unable to grow.
The kingdom that this specific organism would belong to is fungi. Why? Because almost all fungi heavily depend on autotrophs for energy. Fungi can also be multicellular.
Please mark as brainliest, if you found this helpful.