An experimental forest ecosystem is enclosed in a sealed greenhouse. The entire ecosystem, including the air and soil, is treated with an extremely potent fungicide that kills all fungal life stages including spores. What will probably happen next?

Answer: The forest would eventually die.

Explanation:

Fungi (along with bacteria) are responsible for "recycling" all the nutrients in an ecosystem.

For example when an animal or a plant dies, fungi consume all the organic matter and they break it down into Carbon, Nitrogen, Oxygen, Phosphorus and other essential elements, and then release it into que soil or the atmosphere.

If they are removed from an ecosystem, plants wouldn't be able to get these elements, because they would all be "trapped" in complex molecules. As a result, the plants and every organism they act as food to, would die.