Ocean Photosynthesis, What a Plant Hears, Discovery Drones, and the Coolest Plant on Earth
Updated: Dec 2, 2020
“The slow transformation of the ocean and air took more than 2 billion years. Life captured and tamed the sun’s energy; a planet cannot be transformed except by slow and relentless labour on a vast scale. It is not human nature to acknowledge the work of others, and it is unlikely that many of our species will give due recognition to the contribution of numberless green threads thinner than hair from a baby’s cranium.”
- Richard Fortey, Horseshoe Crabs and Velvet Worms
“The goal of life is to make your heartbeat match the beat of the universe, to match your nature with Nature.”
- Joseph Campbell, A Joseph Campbell Companion: Reflections on the Art of Living
1. Our Oxygen Supply
It’s the week before Thanksgiving here in America, a time that encourages us humans to reflect on gratitude. If it’s tricky to come up with something you’re grateful for this year, because 2020 has been a real dumpster fire, allow me to offer a simple option: Oxygen.
Humans breathe in air because our cells need oxygen to create energy and properly function. Pretty great stuff, this gas that allows us to survive on earth, a gas that makes up 21 percent of the Earth’s atmosphere. So who is it we should be thanking for this large and nonstop supply of oxygen?
It may not surprise you that most of the world’s oxygen is produced by plants during photosynthesis. What might boggle your brain is that the plants producing almost all of the earth’s oxygen are not located in the rainforests of South America or in the dense arboreal forests of the northern hemisphere. They’re not even located on land…
Between 50-85% of the oxygen in the Earth’s atmosphere is produced by photosynthesizers floating around in the ocean. Among these oxygen-creators are macroalgae (things we can see with our naked eye) like seaweeds and kelp, as well as microalgae (things we need a microscope to observe) like phytoplankton and single cell plants.
A single-celled algal organism called Prochlorococcus is solely responsible for the production of roughly 20% of the world’s oxygen supply. They do this partly by the species shear numbers. There are a lot of these cells in the ocean and wikipedia states that “It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more.”
Recall that photosynthesis requires sunlight, which means that all marine photosynthesizers need to live in the oceanic layer where sunlight can penetrate, what scientists call the “photic zone”. The photic zone extends beneath the water’s surface about 650 feet. Beneath this zone, such small amounts of sunlight penetrate that photosynthesis becomes almost impossible. But plants continue to surprise us, and ocean botanicals are no different.
Eight hundred and eighty-six feet below the ocean’s surface, a type of red algae called Corallinales is photosynthesizing. Corallinales gets its red color from a pigment which enables it to absorb blue light, one of the only colors from the light spectrum that filters this deep into the ocean. Despite being exposed to only the smallest fraction of available sunlight, this red algae is living and producing oxygen for the ocean ecosystem.
Us land-dwellers may not get up close with the abundant and productive life below the ocean’s surface, but we can work to better understand just how connected we are to these species - if life below the ocean’s surface is threatened, the life above the ocean’s surface is threatened as well.
2. What a Plant Hears
“Imagine that for plants the earth is a kind of twenty-four-hour disco.”
In previous posts, we’ve explored the way plants interact with their environment by using the human senses for comparison. This is not to anthropomorphize plants, but to present concepts that us humans are already familiar with in order to bring the plant world closer to our field of awareness.
Plants see, plants smell, plants feel - but do plants have the ability to hear the world around them? Are they listening. This is actually a more controversial sense than the others to explore in plants. In What A Plant Knows, Danial Chamovitz lays out the various experiments, from Darwin to modern day, that don’t produce evidence of plant hearing that hold up to his scientific standard. He goes on to explain that, using the lens of evolution, a plant may not have the ability to hear because it has evolved other ways of sensing and interacting with its environment. Sound just isn’t one of them.
Stefano Mancuso and Alessandra Viola, in their book Brilliant Green, present a different view, one in which the plants of our world are definitely listening.
To better understand just how a plant might “hear”, let's revisit how human hearing works. The common definition of “hearing” is the ability to perceive sound by detecting vibrations. The organ in humans dedicated to this sense is the ear. Sound waves travel through the air and are captured by the outer ear and sent to the inner ear via the ear canal. The sound waves hit the eardrum, which vibrates in turn and sends an electrical signal via the auditory nerve to the brain for interpretation.
So first things first, plants don’t have ears. But neither do they have eyes and yet, they see. Yet again, in plants, the ability to sense is dispersed throughout the entire organism via mechanosensitive channels. Mancuso and Viola explain this channel with a simple example: “Have you ever been in a disco? If you have, you’ve felt a kind of echo inside your body, somewhere in the belly, produced by the intense vibrations. Even people who can’t hear can perceive this type of sound (generally from the bass at full blast), because our bodies vibrate with the sound waves. Well, imagine that for plants the earth is a kind of twenty-four-hour disco.”
Mancuso experimented with sound waves on a vineyard to see if music affected the yields in the Tuscany wine region. Bose funded the project and the winemakers grew grapevines to the sound of Mozart for over 5 years. The son of the vineyard owner claims that “The plants seem more robust. The grapes closer to the speaker have the higher sugar content, so we believe in this idea.” Mancuso theorizes that the vines may grow toward the speakers because frequencies resemble those of running water. Regardless of why, this research supports the idea that plants sense vibrations and react to them.
Another experiment directed at plant “hearing” confirmed that flowers are listening to bees. Based on observations of evening primroses (Oenothera drummondii), the scientists behind a 2019 study discovered that flower petals sensing the sound waves of nearby buzzing bee wings will in just minutes increase the concentration of sugar within their flowers’ nectar by an average of 20 percent. What’s even more incredible is that the flowers seem to notice but not react to background noise, such as wind. In other words, these plants not only have hearing, they have selective hearing.
The researchers tested over 650 evening primrose flowers in a variety of different experiments to measure nectar production in response to (a) silence, (b) synthetic sound at three different frequency levels, and (c) recordings of the buzzing noise made by bees wings. When they confirmed that there was indeed a response to only certain sound frequencies and to buzzing bees, they removed the petals of the plant to confirm whether or not the sound was being sensed in this tissue. The plants without petals did not produce increased sugar concentrations. The flower, in this case, was acting a lot like an ear.
Evolutionarily, this makes sense. Many plants need pollinators for reproduction, so they have evolved ways to entice animals to visit their flowers. If a flower can get bees to prefer them over others, it has a higher chance of successful reproduction. A flower that pumps out sweeter nectar than its neighbors does just this. Additionally, sweeter nectar may entice bees to feed for longer, which increases the chances that they'll pick up pollen.
This specific study hasn’t yet been peer-reviewed, so its only a step in the direction towards determining just how plants use vibrations to experience the world around them. Other interesting research into the ways plant roots distinguish sound frequencies is coming out. And there are even some scientists who believe roots are making sounds intentionally themselves. “If new discoveries support the theory that the roots can use sounds to communicate among themselves, our idea of plants will again be completely transformed,” Mancuso says.
3. Some super cool things to check out...
A) Drones doing good. If you’re interested in the intersection between botany and technology, this podcast episode is all about a man at the National Tropical Botanical Garden who developed a drone program that is changing the game of endangered plant conservation in Hawai'i.
B) The smallest things can have the biggest impacts. Radiolab correspondent Latif Nasser has a new Netflix series called Connected, which explores the weird and wonderful ways that everything is related. The Dust episode reveals how a dried-up lakebed in Nigeria quells hurricanes in Florida, supports a rainforest in South America, and produces oxygen for the world. It blew my mind.
C) A super old plant I can’t wait to meet. So unusual and yet so incredibly-well adapted, the Welwitschia mirabilis is one of the oldest living species in the world. Some individuals are thought to be over 2,000 years old. The Welwitschias have survived the ice age, fires, pests, people, capitalistic development, local wars — and somehow, even today, there are thousands of them in the Namibian desert.
I had set plans to visit these beauties in March of 2020, and then the pandemic hit. Namibia will be the first place I fly when we can safely travel again, and I will drive my rented 4x4 straight to their homeland in Dorob National Park.