Mycorrhizal networks are connecting trees

Very interesting research shows how trees are interconnected:



Dr. Suzanne Simard is a professor with the UBC Faculty of Forestry, where she lectures on and researches the role of mycorrhizae and mycorrhizal networks in tree species migrations with climate change disturbance.

Dr. Simard writes:

Mycorrhizal fungi form obligate symbioses with trees, where the tree supplies the fungus with carbohydrate energy in return for water and nutrients the fungal mycelia gather from the soil; mycorrhizal networks form when mycelia connect the roots of two or more plants of the same or different species. Graduate student Kevin Beiler has uncovered the extent and architecture of this network through the use of new molecular tools that can distinguish the DNA of one fungal individual from another, or of one tree's roots from another. He has found that all trees in dry interior Douglas-fir (Pseudotsuga menziesii var. glauca) forests are interconnected, with the largest, oldest trees serving as hubs, much like the hub of a spoked wheel, where younger trees establish within the mycorrhizal network of the old trees. Through careful experimentation, recent graduate Francois Teste determined that survival of these establishing trees was greatly enhanced when they were linked into the network of the old trees.Through the use of stable isotope tracers, he and Amanda Schoonmaker, a recent undergraduate student in Forestry, found that increased survival was associated with belowground transfer of carbon, nitrogen and water from the old trees. This research provides strong evidence that maintaining forest resilience is dependent on conserving mycorrhizal links, and that removal of hub trees could unravel the network and compromise regenerative capacity of the forests.

In wetter, mixed-species interior Douglas-fir forests, graduate student Brendan Twieg also used molecular tools to discover that Douglas-fir and paper birch (Betula papyrifera) trees can be linked together by species-rich mycorrhizal networks. We found that the mycorrhizal network serves as a belowground pathway for transfer of carbon from the nutrient-rich deciduous trees to nearby regenerating Douglas-fir seedlings. Moreover, we found that carbon transfer was enhanced when Douglas-fir seedlings were shaded in mid-summer, providing a subsidy that may be important in Douglas-fir survival and growth, thus helping maintain a mixed forest community during early succession. This is not a one-way subsidy, however; graduate Leanne Philip discovered that Douglas-fir supported their birch neighbours in the spring and fall by sending back some of this carbon when the birch was leafless. This back-and-forth flux of resources according to need may be one process that maintains forest diversity and stability

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