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Do plants and soil really ‘talk’? Well, it depends upon how we define ‘talk’, doesn’t it? Surely most folks are aware that plants are not articulate in the sense that they could recite Shakespeare’s 18th sonnet to the soil beneath them. “Shall I compare thee to a summer’s day?. . .” And yet, by the same token, most folks are aware that plant roots do respond to their environment (i.e. the soil) in some very observable ways.
By way of example, one of the most common pieces of advice every budding young gardener receives is to heavily water a transplant to encourage deeper roots. Light watering is to be avoided because it en- courages shallow rooting, which leaves plants poorly prepared for times of water stress. So this understanding permeates our common consciousness from an early age. However, in our modern world we rarely focus our attention upon this ‘hidden half’ of the plant below the soil. We tend to focus most on what the plant produces for us: grain, fruits, vegetables, fibers and flowers.
I can tell you that plants do ‘talk’ on one level simply by responding to their soil environment. The roots of plants are, in fact, very active in modifying the soil to scavenge and extract more water and more nutrients than the soil would give up on its own. I teach in class that roots are not just passively sitting in their soil space, humming to themselves and hoping for a nutrient to jump into their xylem. Quite the opposite, plants spend a great deal of their energy growing into new spaces, retracting from exhausted spaces, and releasing chemicals that increase the availability of nutrients from tiny rocks and soil particles.
Maybe you could say that this isn’t an example of ‘talking’, so much as ‘reacting’. If this is your reaction, I invite you to listen to a Radio lab podcast I recently enjoyed with my children (“From Tree to Shining Tree”; 07/03/2016). What I already find to be a fascinating subject was made all the more incredible when I saw the ‘wow moments’ on my kids’ faces during the entire program. This episode focused on work by University of British Columbia Forestry Professor Suzanne Simard, who has studied the interactions of tree roots with vast under-ground networks of fungal organisms. She has shown over her career that many trees can be connected through their roots by soil fungi, which form a symbiotic relationship with the trees.
She described the fungi as tiny white microscopic thread-like tubes in the soil that function to transport nutrients and water from tree to tree. They are so tiny that a single tablespoon of soil might hold as much as 7 miles of these threads, and the number of trees that might be connected by these tubes in-creased with the age of the trees. One very mature tree was found to be connected to 47 other trees!
What is most interesting about this underground network of roots and fungi is that the trees use them to communicate in undeniably sophisticated ways. Trees warn other trees of disease or insect infestations through chemical signaling. During beetle infestations, for example, young pine seedlings receiving these warnings through mycorrhizal net-works produce different chemical profiles than seedlings without fungi, potentially enhancing their chances of survival.
Pressure on trees from changing climatic patterns provides another poignant example. Stressed and dying trees seem to have the ability to send their carbon to neighboring trees through mycorrhizal networks. This carbon which might be other-wise lost, is instead invested in the survival of a healthier tree. Most interestingly though, this carbon is sometimes selectively sent to new trees better adapted to climate change instead of to trees of the same species. Simard likened this and other equally fascinating interactions of the root / fungi network to a nervous system for a forest superorganism. Now we’re ‘talking’, right?
Apparently, plants don’t have to be as old as trees to communicate this way. Other researchers have de-scribed how resources (food and water) in annual vegetable plants are transported through ‘common mycorrhizal networks’ or CMNs. There appears to be some sort of carbo-economic bargaining between the plants and these networks for ex-change of resources. Who (which plants) receive the best portions is a function of a system of such great complexity that it is currently beyond our understanding. We clearly have a lot to learn about the nature and ex-tent of this awe-inspiring system of communication.
So, do plants react to their environment? Certainly.
Do plants ‘talk’? Well, it just may depend on just how hard you are willing to listen.
