Assimilation is an important part of the nitrogen, phosphorus, and sulfur chemical cycles. Assimilation, sometimes called “uptake,” is the process that plants use to move nutrients that are in the soil into their roots and cell structures.
But how does assimilation actually happen? Are tree roots just like little straws, sucking the phosphates, nitrates, and sulfates out of the soil? It turns out that tree roots are actually really bad at that. Only the very tips of the roots are able to move those nutrient compounds into the plant, and that supplies far less material than the plant needs.
So how do plants take up the nitrogen, phosphorus, and sulfur that they need? In a word: fungus.
There is a network of fungus tubules stretching through forest ground. These fungus tubes invade tree roots, but not to harm: to give. The fungus tubes funnel harvested mineral nutrients (nitrates, phosphates, and sulfates) to the tree, while the tree sends off huge amounts of photosynthesized sugar to the heterotrophic fungi.
The mutualistic partnership is incredible in scope. By some estimates, the trees siphon off up to 80% of their photosynthesized sugar to the fungal network below them. And on the other hand, the fungus is actively mining and hunting phosphates and nitrates to provide to the plant.
The network is massive and surprisingly active. Listen to the RadioLab episode about the fungus-tree partnership (below).