Productive Infections and the Creation of Soil

A robin pulls a worm from the lawn. A brief tension, released, and with a few tosses of the robin’s head the worm is gone.

Dawn on New Year’s Day. It’s my first bird of the year. Hey, my first act of predation too. Great. Behind the robin the lawn gives way to salal and sword fern. Daylight turns large firs from gray to green.

Despite the air of the primordial, today my sympathy is with the worm. Soil and fertility have consumed my thoughts lately, and not just because every ounce of effort and organic matter I put into my garden soil is repaid threefold. I look out my window and see pastures, replanted forest, fruit trees. It’s hard to think of New Year’s as a blank slate anymore.

So, it’s my first worm of the year. And my first chance as a naturalist to get ridiculously obsessed with a small moment and ask a chain of questions worthy of a 4-year-old: But why? How? Et cetera.

It is well known that earthworms improve soil by eating whatever partially decomposed organic matter is in the soil and pooping it out as humus, a substance that holds water, improves aeration and anchors nutrients so that they don’t all dissolve in water and retire to the ocean. It’s that last benefit that raises a first simple and strange question: But why, if some nutrients are inevitably lost to water, isn’t the landscape slowly depleted?

Plants cannot grow without nutrients. Carbon and nitrogen, two of the most important plant building blocks, come from the atmosphere, which is endless. That explains how organic matter can accumulate over time. Photosynthesis is wizardry — matter from air. But equally essential nutrients like phosphorus, calcium, potassium and magnesium come from rock, ever so slowly, which seems to make the recycling of such nutrients from previous plants a thing of utmost importance. Yet decomposition and growth cannot fully be digesting each other, no matter how many worms are around. Plants, worms, birds cannot just be taking, taking, taking — predators of nutrients — or we wouldn’t be host to some of the greatest forests in the world.

How is it we have soil at all? Think of how our terrain began, with glaciers leaving behind raw rock and gravel and the intensely compressed clay and sand we now call hardpan. How, in a mere 10,000 years, do you get from that lifeless terrain to soil with enough nutrients for mammoth trees?

The answer is that life begets life. Living things work hard to sweeten the pot for other living things.

First of all, bacteria are everywhere, eating everything, creating everything. In untold trillions in every field and forest, they are the primary movers and shakers. But beings we can see are sweetening the pot too. Think of that barren post-glacial landscape. What is the first life to colonize rock? Lichen.

Lichen is not a single organism but a partnership between a fungus and algae. The fungus provides a scaffold for the algae. It also has tendrils that exploit cracks in the rock and chemicals to dissolve it, releasing the rock’s stored nutrients. The algae, on the other hand, have the power of photosynthesis, manufacturing sugars. Fungus and algae share their gains to make a living. Together they create a foothold.

Others soon follow onto the rocks. Living and dying, a layer of soil slowly grows. Even today, soil on average is just 5% organic matter, the rest sand and clay. It is cooperation across species that allows life to build in complex webs.

Plants, for example, send up to a quarter of what they produce into the soil through their roots. That’s radical. Why give up hard-earned food? Responding to local conditions, they release ions, sugars, amino acids, and many other compounds to build the soil they want to see and attract bacteria and fungi with helpful skills.

Then there are ectomycorrhizal fungi, which are threadlike fungi that grow only in partnership with plant roots. Put a speck of mineral from the soil under a microscope and you’ll likely find it grooved by fungi. A plant provides EM fungi with carbon obtained through photosynthesis while the fungi create a vast soil transit network for nutrients and water. This is the wood-wide web you hear about. 

Recent research has revealed that EM fungi also excrete acids that eat rock particles and release nutrients. In fact, it is likely that the very first land plants, which had no roots, only survived on land with the help of EM fungi. Fungi taught plants the value of building a network underground that gives as much as it takes. Hence, roots.

Our local red alders “fix” nitrogen by incorporating pods of bacteria into their roots. The bacteria take atmospheric nitrogen delivered by the tree and convert it into forms that can be used by plants. It is such a good system that, in autumn, alders have no need to pull nutrients back from their leaves, which is why alder leaves fall green. An excess of nitric acid floods the soil around alders, feeding other plants and, indeed, breaking down rock particles to release other nutrients.

Even earthworms do more than simply recycle plant material. Recent research has found that a special pouch in their digestive tract holds bacteria that are able to digest rock, releasing the nutrient form of silicon in particular. It’s just like cows. Mammals have a hard time digesting grass, so cows carry special bacteria in their first stomach to digest it for them. While worms themselves may not need the silicon their bacteria produce, plants need it in continuous supply. Happy plants make a lot of plant material. And plant material feeds worms.

What Ellen Wohl writes about young trees applies to animals as well: “A growing sapling thrives to the degree that it can develop its own, interior ecosystems.” Some biologists speak of productive infections. The hallmark of soil is not predation, but collective action based on the sharing of resources.

It would take extreme events to slow life’s crescendo in our soil — the complete churning of the soil, say, which would smash fungal networks and send carbon and nutrients into the air through oxidization; or a total overgrazing that does not allow plants to grow or water to penetrate the soil; or perhaps a rain of poisons.

But that would be crazy. It’s not hard to nurture the soil underfoot. Just let life get to work and chip in where you can.