Mycorrhizal Fungi as per Simard

 

I just finished reading Suzanne Simard’s best-selling memoir “Finding the Mother Tree” (Alfred E. Knopf, 202l) so I thought discussing some of this forest ecologists’ revelations might be timely. For a scientist to receive public notice is unusual, but no doubt we will be hearing more from Dr. Simard for years to come as she promotes some of her more controversial findings.

 

Simard’s career as a scientist began in the 1980s in the vast coniferous forests of British Columbia where she witnessed first-hand the die-off of massive stretches of virginal forests due primarily to an invasion of bark beetles that survived the winters due to the warmer temperatures caused by climate change.
At the time the Canadian forest industry and governmental bureaucracy were all about clear-cutting and reducing competition by eliminating as many low-value species as possible. She railed against this strategy but had little impact on what was official policy. Her breakout as a scientist came in 1997 when her Ph.D. dissertation research received front-page coverage and was published in “Nature,” arguably the world’s leading multiple-disciplinary natural history publication.  This was the equivalent of a first-time-at-bat home run at the World Series.

 

What she demonstrated was that the mycorrhizal fungi network that inhabits forest soils serves as a pipeline between Douglas fir and paper birch with carbon, phosphorus and nitrogen passing freely between these completely unrelated tree species. The fungal mycelium extracted its due of carbohydrates as the other nutrients passed back and forth. This transfer had been demonstrated in laboratory conditions but never under field conditions.

 

Mycorrhizal fungi have been recognized since the middle of the 19th century, but because they inhabit soil and roots, they have always been difficult to study. A dedicated cadre of scientists study them, but most of us would be hard put to name a single scientist working in the field.  
This lack of general knowledge about mycorrhizae is difficult to understand because they form symbiotic relationships with almost every plant on earth and seem to have done so since land plants first appeared over 400 million years ago. Part of this lack of general knowledge about these root fungi may be because our understanding of plant mineral nutrition was occurring at about the same time as the early mycorrhizal discoveries. And if external fertilizer is applied to a growing system, any benefits of the mycorrhizal symbiosis is lost.

 

The word translates from Latin as “fungus root.” Because the fungus mycelium is many times smaller than the smallest root hair and because the hyphae of the fungi spread far and wide through the soil profile and leaf litter, they are much more efficient at nutrient absorption than roots. There are two major types of mycorrhizae — those that are internal in the root and those that form a mat of hyphae over the tip of the root. The internal mycorrhizae (arbuscular or intracellular types) are found associated with 85 percent of all plant families and are the kinds we find in our oak forests. The external types and the main forms Simard worked with (ectomycorrhizal fungi) are found on about 15 percent of the plant families. To complicate things, some of these fungi are generalists and form connections with many plant species while some are specialists and only connect to one kind of plant. And, any given tree in the forest may have dozens of different kinds of mycorrhizal fungi associated with its roots at any given time.

 

A few years after completing her graduate work, Simard took a professorship at the University of British Columbia, where she and her students studied related issues of the mycorrhizal network. These included water transfers during times of drought, nutrient cycling between different species, and what she calls a tree’s ability to recognize its own kin and preferentially share nutrients with relatives and — most controversial of all — the ability of trees to communicate with one another.  

 

For covering such weighty topics, this is a decidedly non-technical book.   would have preferred seeing some technical detail on her work.  While it was interesting to learn a bit about her life, I found her writing style off-putting. Can anyone really remember what bird was singing in the brush along a trail 30 years ago when walking down a mountain path? While she defended her use of anthropomorphism — the assignment of human traits to plants and animals — as a way to reach lay audiences, I couldn’t buy into the concept.  Douglas fir trees have both male and female flowers, so why are they “mothers?”  And, the expansion of the concept of source-sink relationship between interconnected plants to include active and aware communication between individuals seems to me to be an unproven theory, not a proven fact.

 

But she did drive home the message that the natural world is connected in large and small ways and that in its hubris, mankind often takes the expedient path, not the prudent one. Simard’s ultimate role in forest ecology is still to be determined, but her body of work has forced a closer examination of some interesting details.