Tag Archives: photosynthesis

The most powerful family on earth

Prairie grass in the Konza Prairie Preserve in the Flint Hills of Kansas by Betsey CrawfordUntil man duplicates a blade of grass, nature can laugh at his so-called scientific knowledge. 
~Thomas Edison~ 

Such a tiny word — poa, Greek for grass — to encompass one of the great life forces on earth. The Poaceae are the fifth most species-rich plant family with over 11,000 plants. They populate a quarter of the planet’s land and half the United States. Along with forests, they are among the most important stabilizers of both soil and climate. One of the most adaptive plant families, they live on every continent. They’re the top source of nutrition worldwide.  They’re the basis of human civilization. Every one of us is alive thanks to grass. 

We may even have evolved into humans because of grass. There are grass pollen fossils dating from 70 million years ago, but it wasn’t until 5 to 8 million years ago that the vast grasslands we inherit formed. It was a period of cooler, drier climate and water-thirsty forests began to diminish, opening space for the adaptable grasses. The open landscape helped foster bipedalism among primates, which ultimately helped stimulate the development of our large brains.

Anatomy of grass artwork by Kristin Jakob for the California Native Plant Society

Artwork by Kristin Jakob for the California Native Plant Society. Thanks to both for permission to use this lovely piece.

Our hunter-gatherer forebears would have eaten the seeds of grasses along with other seeds, fruits, and tubers. Twelve thousand years ago, they began to plant them. Though we can’t know what seeds the first farmers started with, we do know that all the early civilizations grew with grass. Wheat, barley, and rye in the Mideast. Rice, millet, sorghum  in China. Corn in Mesoamerica. Rice and sugarcane in India and Southeast Asia. Sorghum, millet, and tef in Africa. Over the millennia grasses have fed humans and the animals we depend on. They have built, roofed, fenced, heated, and furnished our houses. Cleaned our air and waters. Formed our soil. Made baskets, boats, and paper. They have cured diseases and powered our cars. 

All this inspires the anthropocentric idea that humans have harnessed grasses to meet their needs and desires. But I like the counter take of some botanists: it’s grass that has bent the human. What better way to ensure your survival than to hook this clever species with the handy thumb and ability to plan for the future? Provide enough nutrients to maneuver them into planting you everywhere they can, every single year for 12 thousand years. Induce their browsing animals to open up more land for you to grow, all the while fertilizing your roots. Convince them to plant 40 million acres of you around their houses. And then spend hours every week lovingly feeding and watering you while fending off pests. That’s power! I toyed with calling this essay ‘Our overlords.’

Worldwide distribution of grasslands. Image courtesy of Missouri Botanical Garden.

Worldwide distribution of grasslands. Image courtesy of Missouri Botanical Garden.

But that has negative connotations, and grass is a miracle. You don’t cover a quarter of a very varied planet without being a highly adaptable genius. In the US we are most familiar with the prairie ecosystem that extends through the midwest from the Gulf of Mexico north into Saskatchewan and Manitoba. South America has similar systems in the pampas and llanos. Trees and grass combine to form the savannas of Africa, India, Southeast Asia, and the Cerrado in South America. The vast expanse of the Eurasian steppes extends from Eastern Europe well into China. 

In the eons before they formed these priceless expanses, grasses evolved several traits that would secure their eventual success. They are wind-pollinated, tossing their pollen to the air. The wind spreads it far and wide, creating a lot of opportunity for pollination over a large area. They form deep roots, up to five times the height of the plant. This vast ecosystem supplies their needs for water, nutrients, and stabilization. And not just for themselves, but for the soil they, and the rest of us, depend on. 

The roots of prairie plants, grasses as well as flowers. Artwork from the Conservation Research Institute.

The roots of prairie plants, grasses as well as flowers. Note the meager extent of lawn grass roots on the far left. Artwork from the Conservation Research Institute

Crucially, they developed a key variant in the photosynthetic pathway. C4 photosynthesis allows for more efficient use of sunlight and water in the creation of carbohydrates. This process allows grasses to use less water, grow in nutrient-poor soils, and allocate more of their biomass to roots. C4 plants are very efficient at pulling in carbon dioxide and sequestering it in their miles of roots. This gives grassland preservation a pivotal role in climate stabilization.

They are also imperative for preserving biodiversity. Grasslands are not only grass. They form a matrix for many other plants that grow with them. The Missouri Prairie Foundation reported that in one of its restored prairies a record of 46 separate native plant species was found in a 20 by 20 inch plot. They provide food and habitat for countless birds, bees, butterflies, mammals, reptiles, microbes, fungi, and other beings that are part of the web of life on earth. They have co-evolved with some of the most majestic life forms on the planet: buffalo, gazelle, zebra, giraffe, elephant. 

Pronghorn antelope in the Pawnee National Grasslands, Fort Collins Colorado by Betsey Crawford

Pronghorn antelope in the Pawnee National Grasslands, Fort Collins Colorado

Grasses both depend on these and domestic grazers to keep land open for them and also have ways to protect themselves from overgrazing. Various toxic phenols and alkaloids, including cyanide, increase as grazing pressure rises. Phytoliths, minute shards of silica, wear grazer teeth down. On the other hand, grasses need grazers, and so keep their budding crowns just under the soil so that they aren’t damaged by nibbling muzzles. As the grazers clean off the upper stalks, new shoots have ample air and light to grow. In the meantime, grazers deposit fertilizer and move on, allowing grasses time to recover.

Some of the most diverse places on the planet are in grasslands. But our tendency has been to treat them as wasted space waiting for us to make them productive. Thus 99% of the American prairie has been plowed, planted, developed. The South American Cerrado is headed in the same direction. Using large, open areas for agriculture certainly makes sense. But the current state of monoculture farming — growing single species annuals with shallow roots, using yearly tilling and high nitrogen fertilizers along with artificial pesticides and herbicides — means that standard agriculture ruins the most important gifts of grasslands. Soil erosion is high, biodiversity and carbon sequestration are low to nonexistent.

This vine mesquite (Hopi obtusa) on a Missouri roadside dangles its vivid anthers, ready to send their pollen to the wind. The feathery stigma at the other end of the filament are ready to receive pollen. Photo by Betsey Crawford.

This vine mesquite (Hopi obtusa) on a Missouri roadside dangles its vivid anthers, ready to send their pollen to the wind. The feathery stigma at the other end of the white filaments are ready to receive pollen.

I love the subtle beauty of grasses with their feathery flowers and am deeply moved by grasslands. I’m not sure where this came from, since I grew up in suburban New York. But one of the most moving experiences of my life was standing in a grassland in South Dakota. I was driving back roads north along the Missouri River, and a stretch took me into the short grass prairie of that dry area. I was up to my knees in sun-filled grasses, flowing like golden water with the wind. It was so hot the air itself was an intense presence. Despite the wind, there was utter quiet. Everything else fell away to nothingness. At that moment, swept into the warm, moving air, I was grass.

As we all are. We share up to half of our genes with grass, a legacy from common ancestors. Sixty percent of human caloric consumption worldwide is grass-based. We are literally grass. We are formed by them and we are inextricably bound into a miraculous matrix of interdependence. To see this clearly is to plant ourselves into the very roots of life. It means we live on earth not as user but as participant, surrounded by equally important partners. We can then hear their message. The skill grass chose us for — our ability to plan for the future — is being called forth to help all of us prosper on our mutual planet.

Pawnee National Grasslands in Fort Collins, Colorado by Betsey Crawford

I’d love to have you join me! If you add your email address, I’ll send you notices of new posts.

Related posts:

Living light: the crucial miracle of photosynthesis

Maple leaves and ferns in the forest on Peterson Bay, Homer, AlaskaTo love plants is to be in awe of photosynthesis. Even when you know how it works, it’s still a miracle. And a crucial, we-wouldn’t-be-here-without-it miracle. Its ramifications are so vast that once it showed up, it dictated all of the evolution that followed.

It’s also complicated. There is, for example, a catalyzing enzyme involved called ribulose 1,5-bisphosphate carboxylase oxygenase, with a personality as confounding as its name. Mercifully, we don’t need to go fully into those weeds. For most of us, it’s magic enough to know that somehow sunlight turns into sugar. But it’s so fascinating that I’d like to invite you to take a walk with me through this lovely, cool forest, and on out into the history of life on earth.

Photosynthesis happening in a forest in the Wynn Nature Center in Homer, Alaska by Betsey Crawford

We’re walking in a sea of green because pigment molecules called chloroplasts in the tree leaves and fern fronds absorb all color wavelengths except the green ones. Those are reflected off the plants, and the highly sensitive cones in our eyes pick up the wavelengths and relay the information to our brains. So we see soothing, cooling green, a color widely associated with the serenity surrounding us in this quiet woodland.

Yet, every leaf and frond around us is pulsing with activity. Photons from sunlight hit the chloroplasts and their energy gets moved from one pigment molecule to another until it reaches special molecules in interior cells. There the energy excites electrons, which makes them pop into orbitals farther from their nuclei. Full of verve, these animated electrons start a cascade through surrounding, helper molecules, creating energy that pulls hydrogen ions into the center of the cell. 

Intense green leaves of red monkey flower (Erythranthe lewisii) and false hellebore (Verastrum viride) mean more photosynthesis. Photo by Betsey Crawford

Red monkey flower (Erythranthe lewisii) and a huge leaf of false hellebore (Verastrum viride). Most of the photos accompanying this post are from the north, where leaves are large and intensely green to capture all the light they can during short summers.

Missing electrons need to be replaced, and this first part of the process replaces them by splitting water molecules and grabbing electrons from the hydrogen atoms, whose remaining ions join the gang in the center of the cell. The oxygen disperses through the stomata, holes in the leaves that open and close as needed. This is the oxygen we breathe. The carbon dioxide we have been exhaling then floats into the stomata to be used in the next part of the cycle.

As the hydrogen ions in the cell’s center get more concentrated, they immediately want back out, pushing their way through an enzyme that creates ATP, the same energy storage molecule that our mitochondria create for us, by a similar electron process.

A wild flower meadow on Hudson Bay Mountain in Smithers, British Columbia., showing the wide variety of leaves for photosynthesis even in one small area.. Photo by Betsey Crawford

A wild flower meadow on Hudson Bay Mountain in Smithers, British Columbia., showing the wide variety of photosynthesizing leaves even in one small area.

Having run through their energy, these electrons enter a new cycle where they are re-energized by more photons to create NADPH. Thus the electromagnetic light energy from the fusion reaction in a star 93 million miles away becomes chemical energy in microscopic cells brushing our shins as we walk, along the way providing the oxygen we need for life. 

The chemical energy — NADHP and ATP — is then used by another process to take a gas — carbon dioxide — from the air and convert it to a solid state in the form of carbohydrates, which are strings of carbon molecules of varying complexity. (This is where the catalyst with the endless name comes in.) Thus carbon dioxide turns into food, as well as being ‘fixed’: removed from the atmosphere and stored in plants. This is why preserving and replanting forests are crucial to reversing global warming.

Prairie grasses in the Pawnee National Grassland, Colorado

Prairie grasses in the Pawnee National Grasslands, Colorado

There are variations in the whole process, even in the woods. The leaves at the top of the trees, in the full glare of the sun, are likely to be smaller and thicker than the understory leaves. That way they protect themselves from the full force of the sun’s energy. The lower leaves tend to be larger, thinner and more horizontal, and the ferns grow many wide fronds, allowing them to catch all the photons they can from the sunlight filtering through the treetops. Because it tends to be cool and moist in the woods, photosynthesis carries on with little hitch.

Once we walk out of the woods into a meadow of grasses, there are challenges that require further variation. In the cool, damp spring, grasses are in heaven, soaking up water and sunlight, feeding their blades and roots, developing seeds. Once summer brings its hot, dry weather, many grasses go dormant until fall or even the next spring. The ones that don’t, like the sturdy crabgrass in your lawn, have adopted photosynthetic habits that allow them to keep going in heat and aridity.

Engelmann's prickly pear cactus (Opuntia engelmannii) in Saguaro National Park, Tucson, Arizona by Betsey Crawford

The pads of cacti are modified stems which do the photosynthesizing. The spines are modified leaves, holding air around the flesh to protect it from the sun. This is an Engelmann’s prickly pear cactus (Opuntia engelmannii) in Saguaro National Park, Tucson, Arizona.

If we walk further on, into the desert, the problems of heat and dryness become acute. Desert plants, like cacti and agave, want to keep their stomata closed during the day to preserve water. Instead, they open them as the evening cools, and have evolved a way to take in and store carbon dioxide in the form of malate at night. This they turn into ATP and NADPH during the day, with their stomata closed. It’s a far less efficient way to provide energy for the plant than the photosynthesizing in our woods, which is why desert and other succulent plants grow so slowly.

In addition to helping maintain the appropriate levels of oxygen and carbon dioxide in our fragile atmosphere, plants nourish themselves and the entire living world. We breathing creatures are carbon-based life: carbon forms the backbone of every molecule in our bodies. We’re entirely dependent on plants’ ability to take the carbon dioxide from our own respiration and not only replace it with the oxygen we need but also to offer those carbon molecules to us in edible forms. That’s what allows us to make our own ATP to fuel this lovely walk among the chloroplasts. Photosynthesis is the most important biochemical process on the planet.

Pacific rhododendron (Rhododendron macrophylla) in Rhododendron Park on Whidbey Island, Washington. Evergreens can perform photosynthesis all year, but are much less efficient in winter. When cold enough, the process can shut down altogether. Photo by Betsey Crawford.

Pacific rhododendron (Rhododendron macrophylla) in Rhododendron Park on Whidbey Island, Washington. Evergreens can photosynthesize all year but are much less efficient in winter. When cold enough, the process can shut down altogether.

Given its importance, it’s no surprise that it showed up relatively early in the earth’s life. Early forms of photosynthesis are thought to have begun about 3.5 billion years ago, its various systems developing over time. Chloroplasts didn’t evolve until 2.5 billion years ago. When photosynthesis began, there was little free oxygen on earth. Early practitioners were microscopic, anaerobic bacteria, most likely using hydrogen sulfide, better known as swamp gas, to do their work. 

About 2.4 billion years ago, oxygen released by photosynthesis began to build up in the atmosphere, leading to what is known as the Great Oxygenation Event. The existing bacterial species weren’t adapted to it and began either to die out or find their way to anaerobic environments. With the evolution of mitochondria, which essentially use oxygen the way chloroplasts use carbon dioxide, species were able not only to adapt but to harness a much stronger energy source. Fueled by this huge boost to metabolism, life on earth blossomed into ever more diverse and complex life forms and ecosystems.

Salmonberry (Rubus spectabilis) in Brandywine Provincial Park, British Columbia by Betsey Crawford

Salmonberry (Rubus spectabilis) in Brandywine Provincial Park, British Columbia

Besides our dependence on plants, there are a lot of wonderful connections among us. We all inherited our carbon from the very beginning of the universe, when the first particles coalesced into mighty mother stars who, with their enormous heat and compression, made the elements that form every subsequent thing. When we give a baby a fresh string bean to munch on, we’re watching 13 billion-year-old carbon join forces in ever new forms.

We share up to 25% of our DNA with plants, remnants of our ancient, shared bacterial ancestors. Mammalian hemoglobin and plant chlorophyll have the same chemical composition, though where hemoglobin is built around iron, chlorophyll uses magnesium. When we eat chlorophyll, it helps hemoglobin with its work of cleansing and strengthening our blood and increasing oxygen uptake. Chloroplasts and the mitochondria we share with plants have a similar history. Each formed when separate species of bacteria found it so worthwhile to join forces that they’re still at it, one cell inside the other, all while wrapped in their own membranes and keeping their separate DNA. Perhaps the most successful mergers of all time. Both make ATP — adenosine triphosphate — the fundamental fuel of the breathing planet.

Ferns in this woods in British Columbia catch the last light of day. Photo by Betsey Crawford

Ferns in this woods in British Columbia catch the last light of day.

Evolution has no need to keep inventing the wheel. If the DNA we inherited from those ancestral bacteria still work, great! If the methods of producing energy work for plants, why not animals? The same plans get reused, with some evolutionary tinkering. Because our building blocks came from those ancient mother stars, people like to say that we are stardust. Via photosynthesis, we are sunlight. Between the systems we inherited from and share with plants and the fact that they ultimately become part of every cell in our bodies, you could also say we’re recycled plants. An idea that, while not quite so lofty, thrills me no end.

It’s all a marvel. I breathe out carbon dioxide and it’s returned to me nicely packaged in carrots, apples, beans, sweet potatoes, squash. Amazing! The history is stunning, all the way back to the carbon formed at the beginning of the universe. We owe thanks to photosynthesis, and its introduction of atmospheric oxygen, for all the blooming, breathing life everywhere on the globe. We owe it every minute of our lives, every thought we have, every bite we eat, every breath we take, every flower and creature we treasure. I love the science that explores and tracks and theorizes about how this fascinating process operates. But ultimately, we are left with wonder. The whole parade is one miracle after another.

Blue clematis (Clematis occidentals) in Waterton Lakes National Park, Alberta, Canada by Betsey Crawford

Blue clematis (Clematis occidentals) in Waterton Lakes National Park, Alberta, Canada

I’d love to have you on the journey! If you add your email address, I’ll send you notices of new adventures.

Related posts: