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 in some very observable ways. For example, common advice given to every budding young gardener is to water a transplant heavily to encourage deeper root growth. We avoid light watering because it encourages shallow rooting. This leaves plants poorly prepared for times of water stress. Understanding this principle of watering occupies our common consciousness from an early age.
However, in our modern world, we rarely focus our attention upon the ‘hidden half’ of the plant below the soil. We tend to focus instead on what the plant produces for us: grain, fruits, vegetables, fibers, and flowers.
Plants do ‘talk’ on one level simply by responding to their soil environment. The roots of plants are very active in modifying the soil to scavenge and extract more water and more nutrients than the soil would give up on its own. Plant roots are not just passively sitting in their soil space, humming to themselves and hoping for a nutrient to jump into their xylem. Plants spend a great deal of their energy growing into new soil spaces, and retracting from nutrient-exhausted spaces. They even release 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 response, listen to a Radiolab podcast I recently enjoyed with my children (“From Tree to Shining Tree,” 07/03/2016).1 I already found this subject fascinating. But when I saw the ‘wow moments’ on my kids’ faces while listening to the program, it became even more incredible. The episode focused on work by University of British Columbia Forestry Professor Suzanne Simard. Her research studied the interactions of tree roots with vast underground networks of fungal organisms. She showed 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. The number of trees that might be connected by these tubes increased with the age of the trees. One very mature tree was found to be connected to 47 other trees!
Trees use this underground network of roots and fungi to communicate in undeniably sophisticated ways. For example, trees can warn other trees of disease or insect infestations through chemical signaling. During beetle infestations, young pine seedlings receiving these warnings through mycorrhizal networks will produce different chemicals than seedlings without fungi. This potentially enhances 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 otherwise lost to decay, is instead recycled and invested in the survival of a healthier tree. More interestingly, 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 described how common mycorrhizal networks move food and water for annual vegetable plants. There appears to be some sort of carbo-economic bargaining between the plants and these networks for exchange of resources. 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 extent of this awe-inspiring system of communication at all levels.
So, do plants react to their environment? Certainly. Do plants ‘talk’? Well, it just may depend on how hard you are willing to listen.
Answered by Jake Mowrer, Texas A&M University/AgriLife Extension