Our world is solar powered. The plants we eat, and the animals we eat after they eat plants, are fueled by the sun. Most of us learn a bit about photosynthesis in school, but fail to appreciate how crucial it is to life on this planet.
As a reminder, photosynthesis is a process that takes place in the chloroplasts of green leaves. Incoming sunlight is captured by the plant and stored as energy in the form of a simple sugar (glucose). The plant performs this miracle by taking carbon dioxide from the air and water from the soil, and releasing oxygen to the atmosphere. Through various chemical reactions, the sugar that was formed in the plant is turned into carbon compounds - carbohydrates, proteins, organic acids, waxes and oils - which are then stored in the plants and in the soil beneath the plants. These are the fuel for life on this planet. Humans and other animals must eat these fuels in order to live.
In order to fuel our vehicles and warm our houses, we currently burn the coal, oil and natural gas that was captured and stored by plants as carbon eons ago - the burning of which has helped create our current climate crisis, with too much carbon dioxide in the air, and not enough remaining as carbon in the plants and soil.
A certain amount of the carbon compounds that were created through photosynthesis - the amount depends on the plant species and soil conditions - will travel down through the plant’s roots and out into the soil. The plant does this in order to attract beneficial microbes into its root zone. These microbes are primarily bacteria and fungi, and their role is to convert soil organic matter (i.e. dead leaves, roots, twigs, other microbes, insects, etc.) into essential nutrients that the plant can use. Those carbon compounds sent out of the roots are delicious to the microbes, which show their appreciation by multiplying their numbers and increasing their production of nutrients for the plant. For example, nitrogen-fixing bacteria make nitrogen available to the plant, and mycorrhizal fungi extend their mycelial threads many metres out and down in the soil to find and bring back phosphorus, water, and the many hard to get micro-nutrients needed by the plants. In this way, plants are made healthy and vigorous by the work of the microbes, which in turn are made healthy and vigorous by eating the carbon compounds provided by the plant.
But the effects of photosynthesis don’t end there. Some of the carbon compounds are converted by the microbes into humus, which is a very stable, long lasting and fertile substance of infinite value to the soil and everything growing on and in it. Fungi produce a gluey substance called glomalin, which also builds humus and improves soil structure so that it better cycles and retains moisture and air, the pH is buffered, pesticides and toxins are inactivated, and nutrients are made available to plants.
This conversion into humus is good not only for the plants and soil, but is key to capturing carbon from the atmosphere and storing it in the soil. Estimates vary, but it is clear that soil, if properly managed, can sequester a large portion of the man-made carbon dioxide gases now heating and choking our atmosphere. What is a crisis in the atmosphere could be a blessing in the soil. Scientists and farmers are working on getting the carbon dioxide out of the air and into the soil via farming practices, especially through regenerative farming. These scientists and farmers are finding that atmospheric carbon dioxide captured by plants and moved into the soil by smart farming practices increases soil fertility and produces better crops.
Those smart practices involve growing lots of green plants for as much of the season as possible.
Where does the home gardener fit into this picture? Well, one home gardener may have a small yard and little impact beyond the neighbourhood, but a million small yards growing plants and capturing carbon can make a difference. All kinds of plants help. Trees, shrubs and perennials are the best carbon collectors and soil builders. Their roots go deep into the soil where they are less likely to be disturbed and the carbon can be stored for years and decades.
Annuals have a smaller impact. The carbon they add through leaf drop and root growth stays in the top layer of the soil and is easily disturbed and returned to the atmosphere as carbon dioxide. Unfortunately, many of our food crops are annuals, and the plot or field where we grow them is left bare of plants for much of the year.
I’ll say more later about the best plants and methods for your backyard carbon capture and storage program. Even if saving the planet is not your thing, all gardeners want fertile soil for growing their nutritious and delicious fruit and vegetables. For that, you want carbon in your soil.