Home & Garden Columns

In some ways, we humans are educating ourselves about the planet that sustains us the way the owner of a cranky old car educates herself about how cars work: We learn about systems and parts when they break down and we’re forced to figure out why. Partly that’s a matter of perceived urgency that gets grants written and funding done—“pure” research is a delicious notion, but it’s rare that anyone can get the time, facilities, and support to study a matter just because we all get intrigued by it.  

Studies aside, there’s the matter of which things get the attention of the broader public. That attention eventually drives some funding, of course, from foundations with close oversight from nonspecialists. And sometimes several foci come together, and something pops up that nobody had imagined. Sometimes that something is the importance of a known fact or substance, importance that is greater than anyone had assumed. 

Lately there’s been media handwaving and even actual information about carbon sequestration. Five, 10 years ago, how many of us had ever heard the phrase, let alone known what it is or why it matters? It matters because carbon in the air, combined with oxygen as carbon dioxide, is a “greenhouse gas”; that is, when there’s lots of it in the upper atmosphere, it helps create that greenhouse effect that’s destabilizing the weather systems we’ve had for a long time, making the world’s air a bit warmer by trapping solar heat that used to escape. It doesn’t take much, just a few degrees, to get glaciers and polar ice caps melting and ocean temperatures rising and currents changing, including upwellings that feed sea life (and then us) and surface changes that make storms stronger.  

Carbon sequestration is an ecosystem service (another new term: the life-support the world gives us) that helps put the brakes on this career. Plants, in particular, make themselves out of elements including carbon. Remember that thing about how they “inhale” carbon dioxide and “exhale” oxygen? They keep that carbon atom and make it into their flesh. 

As long as they live, they keep the carbon they accumulate out of the air. Imagine how much carbon is in a hundred-foot tree, or an acre of grassland or chaparral. When they die and decay, or burn, that carbon goes back up in real or virtual smoke. When trees are cut down, they stop working, even if the carbon in the lumber stays there for (optimistically) a few centuries. The waste, the sawdust, the trampled understory, starts decaying then and there. 

But there’s more to the forest than the trees.  

Under all that green stuff, way down in the dirt, there’s serious and complicated action going on. Roots are growing, absorbing nutrients from the soil, engaging in the dark half of that great dance of making. Roots are permeable, and so is the whole substance of the forest, or the field, or wherever plants grow.  

Trees and many other plants, when we look closely, aren’t isolated, aren’t independent, aren’t even quite separate entities. They absorb what they need from the soil with the help of the mycorrhizal network, the web of fungi under the surface that lives in symbiosis with many plants. People who garden with native plants and who keep bonsai are finding that a bit of soil from a plant’s original home might inoculate its new one with the right organisms to help the plant flourish.  

Mycorrhizae are performing another ecosystem service that has only recently come to light. The USDA published a report by Don Comis on work by Sara F. Wright and Kristine A. Nichols that suggests that a substance called glomalin, discovered by Wright in 1996, does indeed glom onto quite a lot of carbon—27 percent of the carbon in soil. It binds organic matter to mineral particles in soil. It also forms soil clumps—aggregates—that improve soil structure and keep other soil carbon from escaping. 

Glomalin is produced by arbuscular mycorrhizal fungi (order Glomales, hence the name) on plants’ roots, from carbon they trade for other nutrients and water. The fungi produce glomalin, apparently to seal themselves and gain enough rigidity to carry the stuff across the air spaces between soil particles. The fungi grow only on the newest root tips; the glomalin sloughs off the dissolving older hyphae and stays in the soil for seven to 42 years.  

There are ways like no-till farming to encourage glomalin production, but keeping a piece of ecosystem intact in its original form seems to keep the stuff in the soil in greatest amounts. Yet another reason to keep our collective hands off, to avoid breaking what we don’t understand well enough to fix.  

Photograph by Ron Sullivan. 

See the forest for the trees? A lot of “ecosystem services” take place underground, out of sight.