Use the paragraph to answer the question.
About 1.5 million species of fungi exist on Earth. They act as nature’s decomposers. These organisms break down matter and release enzymes and acids that unlock nutrients for plants and soil organisms. You may be familiar with macrofungi, a type of fungus that includes mushrooms. But for the most part, fungi exist as mycelia, tiny threads that snake underground in billions of interconnected threads. They twist and twine with tree root systems, helping tress obtain crucial nutrients. Mycologists call these networks of mycelia "Earth’s nervous system."
Which statement best identifies the central idea of the paragraph?