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A stiff winter wind roared over the fields, taking my breath away and causing my teeth to chatter. The withered grasses whispered as I hunched over, trying frantically to shut the wind out of coat seams and cuffs. Soon snow began to swirl fiercely in mini tornadoes as I made a beeline for an aging oak some early farmer had left standing.
Hunkering down from the wind, I thought this old oak seemed to be the only living thing in this brown winter scene. Don't get me wrong—I love winter; or rather, the beginning of winter. I look forward to the beauty and the cold, but my favorite times of years are when seasons change. The end of winter seems a desperate time — little food; waiting to see if reserves will hold out until rising temperatures bring back a time of plenty to the land.
Maybe the pagans had it right — celebrating the winter solstice as a time when the wheel of the year turns again toward the sun and the days begin to lengthen. Their primitive traditions of worshiping nature reveal an awareness of the sustainability of nature. Each season in its time; the earth renewing itself in the slumber of winter.
Nowadays sustainability is part of the jargon of the green movement, and yet is one of the most ancient precepts of nature. The soil beneath my feet feeds all life on earth and nature has evolved to replenish this precious resource.
At the base of the oak, I reached down to part the curling grasses and reveal the hints of green that would spring forth as winter fades. Clover and trefoil peeked out among the stems. These plants and other legumes are the means of sustainability, responsible for turning a crucial gas, nitrogen, into a form usable by the plants that in turn sustain us.
The expression 'life is a gas' may have some truth to it. Nitrogen, one of the most abundant gases in our atmosphere, is an extremely important element for life on our planet. Every living cell on Earth requires nitrogen, from microbes such as bacteria and protozoa, to the systems of cells that are part of plants and animals. Most of the nitrogen within living organisms is in the form of amino and nucleic acids, the basic building blocks of proteins and genes. Because of these building blocks, basic cellular reactions occur and evolution is possible. These processes are what drive life on our planet.
Nitrogen is undeniably essential, yet its availability is a limiting factor in plant growth. Its presence or absence acts as a control for food availability and population growth on our planet. Nitrogen makes or breaks the circle of life on Earth. The good news is that nitrogen is plentiful. About 78 percent of the air swirling over the fields in which I sat is nitrogen gas (N2). Most of the cold air I inhaled was nitrogen. Despite its abundance, nitrogen in its gaseous form is unavailable to most life forms because of unusually strong chemical bonds. Only a few microbes have the ability to break this link. So the question begs to be asked, if this crucial element is so necessary and yet so difficult to obtain in usable form, how has life on this planet survived and thrived? The answer is quite humbling, and lies underground in the dark recesses of the soil.
In the late 1800s, scientists were studying legume plants such as trefoil, soybeans, alfalfa and clover to investigate why these plants in particular were so beneficial to soil health. These plants had a sort of rejuvenating effect on soil nitrogen levels. Two obscure German scientists, Hellreigel and Wilfarth, discovered that something was living in the soil with these legume plants that raised nitrogen levels. This finding created an immediate sensation, as concern was growing that farmers would soon run out of an adequate supply of nitrogen fertilizer to feed the rapidly expanding human population.
Soon after, the scientist Martinus Biejerinck discovered a mutually beneficial relationship between legumes and the soil bacteria, Rhizobium. At a certain point in the growth of a legume, a chemical is emitted from the plant's roots. The soil bacteria Rhizobium respond to the chemical call and migrate toward the root system. The bacteria in turn emit a chemical that causes the plant's root hairs to bend. The bacteria enter the root hairs and travel deep into the roots. There the bacteria change and begin multiplying rapidly to form a nodule, no bigger than a kernel of corn. During this process hundreds of nodules form on the roots of the plant.
Here the story takes an interesting twist. It is what the bacteria in the nodules do in the name of sustainability that is so amazing. These tiny microbes take N, gas that they gather from the air spaces in the soil and turn it into ammonium (NH,), which is a form of nitrogen that can be used by plants.
Biejerinck discovered that legume plants provide energy to the bacteria in the form of carbohydrates. The bacteria use this energy to gather nitrogen in order to "fix" it into ammonium. The host plant can then use the ammonium for its own life processes. The nodules are connected to the vascular system of the plant to make the exchange of ammonium and carbohydrates possible: sustainability in action.
The discovery of biological nitrogen fixation certainly shook the world with its possibilities. Scientists directed their attention underground, and repeatedly found that the "fixed" nitrogen is released into the soil in usable forms when the plants die and decompose, acting as a fertilizer for future plants. Animals then receive usable nitrogen from eating plants. At last, the mystery of how plants and animals acquire nitrogen was solved, thanks to simple microbes in the soil.
...life in the underground is often based on cooperation between organisms...One of the most important symbioses on earth is that between certain species of plants and a type of soil bacteria with the unique ability to capture nitrogen out of thin air... It is these specialized creatures of the underground that control much of the global nitrogen cycle and keep it churning fast enough to support us all. These species evolved slowly, over the course of hundreds of millions of years... Over evolutionary time, what was inaccessible or considered "waste" becomes "food' for new life forms. From this perspective, you could say that scarcity has served as the fertilizer for the evolutionary tree of life.
--David W. Wolfe, Tales from the Underground: A Natural History of Subterranean Life
Thanks to some simple life forms, our tree of life continues to evolve. We humans have a long way to go in studying the natural system of sustainability that has been in place for millions of years. We have in a short time developed a process for making synthetic nitrogen fertilizers. The process however, is costly. The monetary investment in a fertilizer plant is not small, and yet nearly one-third of the world's population is fed as a result of the process that makes synthetic nitrogen fertilizers. Of course this 'progress' presents side effects. The disruption of the nitrogen cycle by human activity plays an important role in a wide range of problems including smog, contamination of groundwater and acid rain. Despite our remarkable technology and advances, we still cannot compete with what nature has created and evolved over millions of years.
Understanding the miraculous process driven by nitrogen fixing bacteria is humbling. Humans have barely begun to understand the complex processes carried out by microscopic one-celled organisms. Under my feet, beneath the seemingly dead winter landscape, the engine of life chugs away, feeding the plants that feed us and sustaining life as we know it. Human ingenuity may have found other ways to make nitrogen fertilizers, but our innovations are infantile compared to the natural process occurring underground. Nitrogen-fixing bacteria do it cheaper, faster and better. Our lives depend on the microscopic world and the services these tiny life forms provide. Because of these microbes of the underground, life is sustained and evolution moves forward. Life is, indeed, a gas.
