As a gardener, I routinely kill hundreds, probably thousands, of plants every week. When I weed, I attempt to knock as much soil as possible from the roots back onto the ground before removing a plant to the compost pile. I often find earthworms entangled in the root balls and I try to gently return them to the Earth as well. I wonder if they feel disoriented, plucked from their occupations, and plopped abruptly onto the soil surface, no longer nestled in the subterranean root bundle where they were busy worming. When they burrow back down into the soil, are they content to start worming again in their new location, or do they feel out of sorts, unfamiliar with their neighbors? To maintain productivity, I try not to feel too bad about the unintended consequences of my actions…it’s hard to imagine what perception must be like for a worm, or for the plants that I diligently cull. And what about all the tiny creatures I can’t even see? What happens when I rip a plant out of the ground, wresting its roots from the grasp of the Earth? What microscopic worlds am I disturbing when I decide that something is a weed, and I don’t want it there?
Soil is where most of the biodiversity on Earth exists, and the small volume of soil that clings to and surrounds plant roots sustains life as we know it on Earth. Called the rhizosphere, the couple of millimeters of soil that embrace plant roots contains a dynamic mix of organisms. A teaspoon of healthy garden soil has been measured to contain up to a billion bacteria, several yards of invisible fungal hyphae, thousands of protozoa, and dozens of nematodes, representing from 10,000-50,000 different taxa. Plants themselves influence the species present in the rhizosphere by way of their root exudates. The presence of particular carbohydrates and proteins coming from plant roots stimulates, attracts, and increases the specific bacteria and fungi that benefit those plants. These organisms represent the foundation of the soil food web; larger microbes such as nematodes and protozoa consume them. Their waste excretions in turn are absorbed by plant roots as a food source. Nematodes and protozoa are prey for soil arthropods, such as insects and spiders, and so the web expands and extends above the soil, eventually incorporating all life on Earth. The interactions taking place between and among soil organisms through the cycles of life, symbiosis, decay, and death are complex and dynamic. Minerals and nutrients are conserved by being recycled through different life forms; a decaying body becomes an ephemeral nutrient pulse for the ecosystem.
Soil microbes and decomposers are the link between life and death on this planet. They are the magic, the drivers of transformation and eternal life. What happens when I plunge my soil knife into their universe to remove an offending plant and its roots, to serve human aesthetic values? Sometimes while pondering these mysteries I must remind myself that despite the many collective unforeseen consequences of modern human lifestyles, we are a part of the Earth. All organisms, from microscopic entities to whales, are expressions of the ecological matrix they emerge from. I am a human and a gardener, and to have an impact on my surroundings is an inevitable part of existence on Earth. There is no escape from interconnection.
Only relatively recently have scientists begun to map and define soil microbes and analyze their individual and communal roles in ecosystems. What they are discovering is that microbes are the driving force behind the carbon and nutrient cycles that sustain all other forms of life. Unfathomable numbers of virtually invisible life forms are integral to every living thing we can observe. In fact, the last universal common ancestor for every life-form on the planet was bacterial. Furthermore, these microscopic lifeforms are intelligent. Bacteria, protozoa, amoebas, and even single cells exhibit complex adaptive behaviors, skills, and discrimination normally thought to occur only in “higher” multicellular creatures. Microscopic life forms communicate and share information, within and across species. Bacteria, for example, emit signaling molecules that lead to altered gene expression at a high enough concentration. They even exhibit linguistic patterns and a highly developed social capacity.
Human life is inextricably connected to soil life through the many vital services provided by a living soil, including the cultivation of plants for food, medicine, fiber and building materials, water purification, nutrient cycling, carbon sequestration, and detoxification or buildup of pollutants. And human actions certainly affect the Earth’s soil communities. Modern agricultural practices such as tillage and chemical use result in declining soil health and biodiversity and drastically increase soil erosion. Under natural conditions, it takes at least a century for an inch of living soil to form. Rampant sprawl and development scrape topsoil and plant life out of the way and entomb it beneath cement and asphalt. How does this affect the microbial world? And how will it affect us? Microbiologist Carl Woese has said, “If you wiped out all multi-cellular life-forms off the face of the earth, microbial life might shift a tiny bit…If microbial life were to disappear, that would be it–instant death for the planet.”
How can we learn to be proper stewards of the microscopic beings supporting life on Earth? Where do humans fit into the cycle of life and death and rebirth? What do we collectively want to leave behind when our buildings and our bodies are returned and recycled, from dust to dust? Perhaps, I muse, the plant world is our visible connection to the invisible world that sustains us all. If we change the way we interact with plants in the landscape and in our gardens and farms, we can positively affect the web of life.
Jessica Burns has been working at the Holden Arboretum since 2018. She began as a seasonal laborer and now works as a part-time gardener. Jessica has studied herbalism and organic farming for over ten years. She loves propagating plants from seed and hopes to have her own nursery someday. Jessica hopes to affect change in the world by promoting perennial food systems and planting trees.