Mycorrhizal networks and mother trees – what is theoretically possible?

Mycorrhizal fungi connect with plant roots and facilitate exchange of nutrients (N) and carbon (C) in a symbiotic relationship between fungi and plants, sometimes linking multiple plants in a mycorrhizal network. The question is, do such networks support resource sharing among plants?  In this talk I will discuss potential mechanisms of resource transfer among plants and their plausibility based on current theory and empirical knowledge. Mycorrhizal networks have sparked a huge interest not only among ecologists but also in popular media, where it has become a “wood wide web” claimed to serve as the trees’ internet for communication and as a social support system for sharing resources. As the stories have moved far beyond the scientific evidence, a debate has started among scientists about the true nature of the network and its ecological role. Because of the dynamic and cryptic existence of fungal hyphae underground, and the many other potential ways resources can move in the soil, it has been difficult to obtain reliable quantifications of C and N transport between plants through the network. In absence of empirical facts, theoretical models may guide us in terms of what is possible or likely, based on the principles of nature and our current state of knowledge. The classic C-N trading relationship between single plants and fungi is well established and more recent market models can also explain differentiation among multiple trading partners, as well as stabilizing ecosystem level feedbacks. It is more challenging to explain resource transfers in the opposite direction, such as a C transport from fungi to plants, which is necessary for trees to supply carbon to other trees via the mycorrhizal network as implied by the mother-tree hypothesis. Do we need more complex market models, or are there completely different mechanisms at work?