From Quanta Magazine:
Key to this picture is the revelation that the unseen underground world is just as complex, sophisticated and purposeful as the visible aboveground world we inhabit. Microbes are not simple, passive accessories to plants, but dynamic, powerful actors in their own right. Fungi can hoard nutrients, they can reward plants that are generous with their carbon reserves and punish ones that are stingy, and they can deftly move and trade resources to get the best “deal” for themselves in exchange.