Can Plants Think, Feel, See, Hear, and Smell?

I can’t imagine Rod Stewart and Ronnie Wood (Faces) were thinking about agronomy when they sang their song ‘Ooh La La’, with its classic chorus, “I wish that I knew what I know now when I was younger“. But it can be life-altering if you’ve ever played that reflection game. How I think about agriculture has drastically changed over the years, and it is more of a philosophical difference than a technical one.

The Early Days

I have never been overly dogmatic about farming practices. Early in my career, I recognized that there are many ways to grow good food sustainably. But, looking back over my 35 years in agriculture, there has been a strict boundary between humans and plants. I learned that plants were not sentient beings, incapable of “consciousness”, hardwired and genetically determined to respond to environmental stimuli. Despite being a staunch believer in metaphysics and other ideas that are not explained via biology, chemistry, and physics, I was never comfortable expressing my belief that plants are sensory beings capable of thinking, feeling, seeing, hearing, and smelling.

For many reading this article, the previous sentence is enough for them to stop reading. However, I am not trying to equate the sensory evolution of animals with that of plants. The academy has done a great disservice in not recognizing the complexity of plants, particularly their millions of years of co-evolution with microbes. Plants don’t have a central nervous system, a brain, or an endocannabinoid system that coordinates information for the entire body like animals do. Yet, plants use chemical signals that act as fast neurotransmitters and can have interspecies communication that far exceeds the ability of humans.

So, using more recent examples of our increased understanding of the plant:soil:microbial interface, I want to highlight the importance of discerning facts versus theories when implementing “sound” agricultural advice.

How Plants Eat

Most plant physiology textbooks point to three ways plants take up nutrients:

• Mass flow (water movement via transpiration)
• Diffusion (nutrient gradients)
• Active transport (proton pumps)

Whether discussing conventional or organic farming, the above has been the dominant belief for decades. Recently, researcher James White has brought attention to another way plants eat: the rhizophagy cycle. Microbes enter the plant root at the root cap; the plant then uses oxygen (superoxide) to digest some of the microbe cells to retrieve nutrients and discards the remaining microbe via root hairs. This ‘mining’ of microbes by plants may help explain why many farmers with high soil organic matter do not see nutrient deficiencies in their crops despite not adding the recommended fertilizer rates. A common estimate suggested that each percent of soil organic matter was the equivalent of 10 to 15 pounds of nitrogen per acre per year. But we now see farmers with 5% soil organic matter having superior yields with little or no additional fertilizers.

How Plants Talk

Once again, most agroecology textbooks note yield losses when crops aren’t grown in monocultures, or that competition from weeds will impact yield. University of British Columbia researcher Suzanne Simard showed that in natural ecosystems, plants, with help from fungi, communicate with each other. Her research highlighted that they communicate (i.e., exchange hormones and signal messengers) and share nutrients like water, sugar, and trace elements. The notion of survival of the fittest is not surprisingly the thought paradigm in modern agriculture, despite Nature providing constant examples of ‘better together’.

Plants are Similar to Humans

Plants and humans share many of the same genes, and, as evidenced by transgenics, animal genes can be placed into plant genes. The similarity at a DNA level is exciting but doesn’t stop there. The relatively recent discovery that humans, in terms of cells, are more bacteria than anything else has brought attention to the notion of the microbiome, especially of the gut. The gut microbiome is responsible for much of our nutrient absorption, as well as our immune system and hormone production (i.e., 90% of our serotonin and 50% of our dopamine). The parallels for plants are striking. The phytobiome, most notably the rhizomicrobiome, is the plant’s gut and similarly plays critical roles in nutrient uptake and plant health, including immune responses.

These examples showcase how our separation from plants and Nature can lead us to false understandings of the observations we make, even in our research. Whether we place fault on extrapolations from reductionist science or our species’ hubris in needing answers, when we create divisions, we lose the interconnectedness that is a prerequisite for sustainability or, more importantly, regeneration.

Much of the agronomy I was taught when I was younger was based on a worldview that plants have no agency, hardwired to respond to inputs that we can manipulate. This mentality has led to a never-ending parade of technological fixes in attempts to keep the system functioning. In contrast, a worldview that recognizes the wonder and awe of plants and is humble enough not to know all the answers is what keeps me wanting to learn more.

I started this article with a song and will finish with one. “Ah, but I was so much older then, I’m younger than that now” (My Back Pages, Bob Dylan).