It’s early autumn, and the oak tree in an untended corner of your neighbor’s yard is shedding its leaves. One dry leaf flutters down between tall blades of unmown grass and settles on a patch of bare soil. At first, not much happens, because the leaf is too dry to be appetizing to any of the soil’s many denizens (we’ll assume your neighbor doesn’t spray pesticides or herbicides on this corner of her yard, as these chemicals greatly diminish soil life). Also, this leaf, like most, contains nasty-tasting compounds to protect it from munching insects. The next morning, though, dew has wetted the leaf, and the protective chemicals have begun to leach out. A light drizzle accelerates the washing process. The leaf droops moistly against the soil. When the leaf is rinsed free of polyphenols and the other bitter-tasting compounds and tenderized by moisture, the feast begins.Among the first at the table are bacteria that have lain dormant on the leaf surface. They revel in the moisture and begin to bloom, secreting enzymes that tear apart the long chains of sugar molecules composing the leaf cell walls. In just hours, the leaf is speckled with the dark blotches of bacterial colonies. Wind-borne spores of fungi land and burst into life, and soon the white threads of fungal cells, called hyphae, knit a lacework across the leaf. Fungi possess a broad spectrum of enzymes able to digest lignin (the tough molecules that make wood so strong) and other hard-to-eat components of plants. This gives them a critical niche in the web of decomposers; without them, Earth might be neck-deep in fallen, undecomposable tree trunks.

Moistened by rain and softened by microbial feeding, the leaf quickly succumbs to attack by larger creatures. Millipedes, pill bugs (isopods), fly larvae, springtails, oribatid mites, enchytraeid worms, and earthworms begin to feed on the tasty tissue, shredding the leaf into small scraps. All of these invertebrates, together with bacteria, algae, fungi, and threadlike fungal relatives called actinomycetes, are the first to dine on rotting organic matter. They are called the primary decomposers. Earthworms are the most visible and among the most important primary decomposers, so let’s watch one as it feeds on our leaf.

The earthworm grabs a leaf chunk and slithers into its burrow. With its rasping mouthparts, the worm pulverizes the leaf fragment, sucking in soil at the same time. The mixture churns its way to the worm’s gizzard, where surging muscles grind the leaf and soil mixture into a fine paste. The paste moves deeper into the earthworm’s gut. Here bacteria help with digestion, much as our own gut flora helps us process otherwise unavailable nutrients from our food. When the worm has wrung all the nutrients from the paste, it excretes what remains of the leaf and soil, along with gut bacteria caught in the paste. These worm castings coat the burrow with fertile, organically enriched earth. Before long, hungry bacteria, fungi, and microscopic soil animals will find this cache of organic matter and flourish in walls of the burrow, adding their own excretions and dead bodies to the supply.

Fueled by the leaf’s nutrients, the worm tunnels deeper into the ground, loosening, aerating, and fertilizing the soil. Rain will trickle down the burrow, threading moisture deeper into the earth than previously. The soil will stay damp a little longer between rains. In spring, a growing root from the oak tree will find this burrow, and, coaxed by the easy passage and the tunnel’s lining of organic food, will extend deep enough to tap that stored moisture. The worm, with its fertile castings and a burrow that lets air, water, and roots penetrate the earth, will have aided the oak tree and much of the other life in the soil. Worms are among the most beneficial of soil animals: They turn over as much as twenty-five tons of soil per acre per year, or the equivalent of one inch of topsoil over Earth’s land surface every ten years.

Meanwhile, on the surface, the feasting invertebrates continue to shred the leaf into tiny bits—or comminute it, in soil-specialist parlance. Comminution exposes more leaf surface—tender inner edges at that—to attack by bacteria and fungi, further hastening decomposition. Also, the small army of mites, larvae, and other invertebrates feeding on the leaf deposit a fair load of droppings, or frass, which also becomes food for other decomposers (a microscope reveals that many decomposing leaves are thickly covered with frass, which adds up to an enormous amount of fertile manure). Any leaf bits that aren’t fully digested on their first passage through a decomposer’s gut are eaten again and again by one tiny being after another until the organic matter is mashed into microscopic particles. Soil invertebrates such as worms and mites don’t really alter the chemical composition of the leaf—their job is principally to pulverize litter. Their scurrying and tunneling also mixes the leaf particles with soil, where the fragments stay moist and palatable for others. In some cases, the animals’ gut microbes can break down tenacious large molecules such as chitin, keratin, and cellulose into their simpler sugarlike components. The real alchemy—the chemical transformation of the leaf into humus and plant food—is done by microorganisms.

As the soil animals reduce the leaf to droppings and microscopic particles, a second wave of bacteria, fungi, and other microbes descends on the remains. Using enzymes and the rest of their metabolic chemistry sets, these microbes snap large molecules into small, edible fragments. Cellulose and lignin, the tough components of plant cell walls, are cleaved into tasty sugars and aromatic carbon rings. Other microbes hack long chains of leaf protein into short amino acid pieces. Some of these microbes are highly specialized, able to break down only a few types of molecules, but soil diversity is immense—a teaspoon of soil may hold 5,000 species of bacteria, each with a different set of chemical tools. Thus, working together, this veritable orchestra of thousands of species of bacteria, fungi, algae, and others fully decompose not only our sample leaf but almost anything else it encounters.

I'm working on making a permaculture eden / food forest ; Gaia's garden is a really nice book full of inspiration for us!
As we start to coop with the world of invisible massive interconnection, a new relationship with Mother Nature can emerge.