Pedogenesis: Making a Home
The world is so diverse because it is made up of individuals confronting and improving their unique circumstances through cooperation, evolution and time.
The word “pedogenesis” is from the Greek – pedon: soil, ground and the Latin – genesis: generation, creation and together they mean: the making of soil. In scientific literature the story is pretty much always framed as the ‘making of’ soil and not the ‘made by’. I want to try telling the story about the ‘made by’ - how non-human individuals acting together build soil and by extension the biosphere. I am not trying to make this just some fanciful re-telling. I think re-framing the story this way has something very practical to tell us about how to live in the world.
We seem to have a hard time ceding any primacy to anything but ourselves. Everything we talk about we relate back to us. I get that it’s hard to imagine anything but oneself as a standard to judge and act by. It is nearly, but not quite (!) impossible to imagine other minds, particularly those that do not look like nor operate like ours.
We have worked hard to erect and fortify an imaginary wall between ourselves and every other living thing. It is as if the bite of the first apple gave us a particular kind of self-awareness that manifests as a story we tell ourselves, that literally cast us from paradise, separating us from every other living thing.
In an amazing, brisk 177-pg book called The Sentient Cell, Arthur S. Reber, Frantisek Baluska and William B. Miller, jr. (2023) describe a theory called the Cellular Basis of Consciousness (CBC) that completely flips the narrative about sentience. They claim that what we have missed about consciousness - that it is shared by all of life - is because we started with us as the model. We are recipients of millions of years of evolution. What we do with our minds makes it seem like they and we are so special that we must constitute a completely different kind of life - the only kind with self-awareness.
Baluska, et.al., (2022) point out that in science the most effective investigative strategy is to start with smaller, simpler explorations and over time as understanding deepens, develop more complex investigations. This is how the course of the natural sciences – physics, chemistry, geology and astronomy – progressed; while the life and social sciences began with us, the most complex system as the standard model all others were compared against.
Evolution ensures that valuable adaptations are handed down and improved upon generation by generation. Consciousness would have helped early, simpler life forms survive to become more complex by conferring the capacity to handle novelty. All beings have some built-in (reflexive) programming plus the ability to behave in novel ways in the face of novel circumstances. Life samples the world, forms hypotheses, then tests and acts upon them in order to minimize surprise. The less surprise the better, really.
Each plant is a living world-builder, however small that affected world may be. They may be surrounded by genetic copies of themselves, by relatives, companions and competitors, all growing into the world. Each plant begins to change the place the moment they arrive and continue to change it even after they are gone. Plants can propagate with or without mixing genes. They can cover vast distances and engage the world at very fine temporal and spatial scales. Individuals grow into communities and extend their reach via relationships with other individuals and other individuals of other species, like mycorrhizal fungi.
Roots evolve inside pore spaces, structuring them, creating a sphere of life around each root. This living zone around the root is known as the rhizosphere. The roots establish themselves by re-jiggering the ground. As roots grow, they push on the dirt particle by particle. They re-orient dirt packing. They build, organize, and connect pores. They initiate and maintain a host of biogeochemical processes that are continuously changing the air, liquid, and solid properties of the medium they are inhabiting.
Root tips exude a fluid photosynthate mix that helps loosen and soften the way in front of the growing tip. These exudates include carbohydrates, proteins, chelators (for solubilizing mineral nutrients and metals), amino acids and other organic compounds that create a microbial and fungal feeding ground around the root. Through two-way exchanges of water, carbon, minerals, structure and information the root establishes relationships with microbes, fungi, and other plants.
Mycorrhizal hyphae establish mutualistic relationships both inside and outside the roots. Plants provide photosynthetic carbon and water while the fungi return mineral nutrients like phosphorus and nitrogen and sometimes water, particularly during dry periods. Mycorrhizae hyphae are roughly 2-3 orders of magnitude smaller than the smallest roots and can reach into and bridge pores that roots cannot. They can help confer to plants resistance to drought, salinity, heavy metals and root pathogens.
The fungal networks and microbes also release exudates like sticky, hydrophobic glycoproteins, and dead cells that together with root exudates turn small aggregations of soil into larger aggregations. The fungi also build, structure, and connect their own pore spaces; their own mycorrhizosphere (Leake, et.al., 2004). They can carry carbon from plants into soil regions far beyond the conventional root rhizosphere. They can have many different, simultaneous relationships with individual plants (Simard, 2009).
The roots, fungi and microorganisms inevitably die and decay. The hypha and microbes tend to have the shortest life spans, in terms of days or months. Fine roots have a broad range of lifetimes that can range between days and years. Some woody roots last decades. The dead and dying roots literally make way for new roots. They leave both the evidence of their bodies, like the pores they built, as well as their actual bodies. The pore network the older roots built gets re-occupied by the new, “quick-witted” roots.
The root itself is a living pipe. As the sun, temperature, water vapor gradient and stomata permit, transpiration draws water out of the plant. This force acts like a vacuum sucking out the water, just like sucking on a straw. The vacuum pulls water out and pulls in the root walls. The root diameter can decrease by more than half during the heat of the day. As the transpiration suction force abates the root relaxes back to its original shape.
Other forces too, like freeze-thaw, winds bending stems aboveground, rain drop splatter and soil slippage help create space around the root. This annulus, a ring-shaped opening between root and pore lining, grows and breaths every day. Water is moved inside the living pipe and around it, through the ever-changing annulus space.
Some researchers, like Phillips (2008), talk about soils as an ‘extended phenotype’ of the plants that built them. That is, life does so much work to the soil’s observable characteristics that soil can be considered the expression/manifestation of a particular set of genes. The soil is the signature as much as an indicator of a particular plant community.
These place-changing capacities have splayed out over the earth in a mosaic of terrestial plant communities, magnifying their effects. The Gaia theory, developed by James Lovelock, says that the earth functions like a unitary organism, optimizing conditions for life globally. In contrast, the concept of directed evolution is that the global ecosystem is the product of evolving and interacting individuals doing the work together (Lapenis, 2002).
The directed evolution theory, developed by several generations of Russian scientists in the late 19th and early 20th centuries, holds that the evolution of the planet is built by the “superposition of micro-forces controlled on local and regional scales, driven by the universal criteria of biogeochemical selection” (Lapenis, 2002). Another way to say this might be - it is the overlapping actions of countless individuals and collectives performed over every moment of every day for millions of years that has and continues to build this world.
The fierce debate about how much cooperation or competition shapes the world seems to me quite lopsided. The reality is cooperation led to co-optation, literally. Multi-celled organisms were built via symbiotic relationships between unicellular organisms. Lynn Margulis demonstrated that organelles like mitochondria and chloroplasts were originally independent organisms that merged into a symbiotic relationship with other one-celled organisms to create multi-celled organisms. Cells with a nucleus are more like tightly knit communities than individuals, just like our own bodies are composed of tightly knit communities. Evolution’s lesson in the long-term is that cooperation and symbiosis are the keys to dealing with change and having ancestors.
Pedogenesis, powered by climate and plant communities, moves toward more structured soils over time (Lin, 2010). It builds a range of soil features that indicate maturity and relative age (e.g., Jenny, 1941). Soil structure can be visualized as a three-dimensional arrangement of organic and mineral materials. This structure is key for nutrient, gas and water fluxes. The combination and variation among individuals each meeting a unique space and making it their own, helps lead to the diversification of spaces.
The partitioning of water at the soil surface of natural, vegetated landscapes is largely controlled by plant communities. Water fluxes moving through the rooting zone are essential to life and the processes of bedrock weathering and soil development. The positive ecohydrologic feedbacks that form lead to enhanced weathering and expansion of the rooting zone. As soil develops, plants extend their influence leading to more and better-connected porosity, more plant available moisture, intensified nutrient cycling, more redundance, more connectivity and the evolution of the capacity to better withstand drought and flooding extremes.
Plants direct the rooting network in the name of managing water and the energy of water moving through the ground. The characteristic root branching patterns develop in the same manner as rivers and lung airways, to help mitigate the variation of energy “surprises”. This network of interconnected pores continuously evolves (Nieber and Sidle 2010). Water runs through decayed root channels and channels occupied by live roots. Water also flows inside and outside of mycorrhiza hypha. Channels associated with these inter-connected, dynamic rooting networks act as preferential flow paths and networks of continuously evolving connections across hill and dale.
A considerable amount of ink has been spilled about preferential flow paths. This phenomenon, often measured with infiltration testing to determine how fast the water enters the ground, shows significant variation - multiple orders of magnitude across the same patch of earth. To me, that heterogeneity is not anomalous, but a feature of the living ground. Each plant orders the world in response to where it finds itself. As life has evolved up to now, it has become ever more idiosyncratic, helping to build the rich, diverse mosaic of communities and homes that populate this earth.