Another Life: Probing the pedosphere for masters of the underworld
No organism is more important than the ant to the complex ecology of our soil
Ecosystem engineers: ants can alter the properties of soil. Illustration: Michael Viney
Mweelrea, the bald king, wears a gleaming skullcap of hail. Hoar frost has crisped the grass to the rain gauge, and a tender begonia has crumpled in its pot outside the door. So the jet stream could give us that sort of winter, or perhaps the Gulf Stream, slowed by the flood of the Arctic’s freshwater.
Cued by the sag of the begonia, I am awed all over again at the prospect of the acre’s winter dissolution, the tonnage of fallen leaves, soft stalks, late flowers, the huge biomass that must somehow disappear into the soil. Our own few decades of tenure have added to its weight, not least in the nettles and briars that now seek, over-eagerly, to weave our wreaths.
There’s a textbook term, the “pedosphere”, not at all what the word might first bring to mind but the outermost skin of Earth. Its miracle of nourishment has been much abused by the anthropocene, the age of man, with its pollutions, impactions, degradations, interments. Not alone by linguistic accident, surely, do the Americans call soil “dirt”.
Now that our species has cause to fear for its long-term security of tenure, soil is reckoned part of our “natural capital” in the spreadsheet for survival. Its appetite for carbon has been added to the long list of credits for sustaining human life.
A seminar on Monday, World Soil Day, at the National Botanic Gardens in Dublin, marks the Irish launch of the People4Soil campaign (people4soil.eu), a network of concern for soil protection already well promoted in Europe. There’s no special care for soil in the EU’s nature directives, so “citizens” are being urged to press for it now.
Among the most receptive will be the growing legion of home gardeners for food, busily layering their autumn compost heaps. When Matthew Jebb, the National Botanic Gardens director, invites them to “a new understanding of intimacy” in the relationships of soil and plants, they’ll be all ears.
Teeming, myriad life
The teeming, myriad life of the soil has been almost as little explored as the far layers of the ocean; its sheer numbers and complexity are overwhelming. While some countries have begun to piece together a baseline inventory of the subterranean world, Irish ecologists have come late to what some of them have called “the last frontier of biodiversity research”.
We have produced the first maps and monitoring of this island’s great range of soils, their chemistry, geology and humus. We know a lot about our earthworms, large and small, prime shifters and mixers, aerators, decomposers and crumb-makers in the nourishing crust of the pedosphere.
But they are big beasts of a world that teems with smaller and microscopic life. Worms do indeed drag leaves into their burrows (cleverly, by the sharp end, as Darwin observed). But ants and millipedes, springtails and bristletails, mites, spiders and nematodes all join in the feast that reduces leaves to skeletons (these left for the snails). A single gram of soil can hold 5,000 or more species of microbe, some shredding cellulose into simpler, digestible molecules.
Much of the “new understanding of intimacy” between plants and soil rests on research into the mycorrhizae, fungal growths that, attaching to roots, contract a symbiosis with the great majority of plants. In exchange for carbohydrates from the plants, the fungi forage further to bring minerals, such as phosphate, essential to plant growth. Some pipe water into tree roots, giving conifers, for example, less need to spread their soil anchorage in forests.
So diverse is soil biology, so myriad its forms, that agreeing on its “keystone” organisms can be difficult. In the recent CréBeo project, the first such survey in 50 years, an ecological team was recruited by the Environmental Protection Agency to explore the important life in different soils and the need to protect, in particular, their ants, long known as ecosystem engineers (epa.ie/pubs/reports/research/land/strive67)
Hunter-gatherers, sometimes farmers (of aphids) and formidable artisans, ants can alter the properties of soil. Their nests and mounds are nutrient hotspots, scavenged by co-existing insects. Even the abdomens of ants, so the CréBeo scientists discovered, hold unique bacterial genes, not found in soil, that may fix nitrogen from the air.
Before intensive farming, which found them an obstacle, anthills were common in unploughed grassland. Now ants are quite missing from Ireland’s arable fields and dominate the fauna only in semi-natural, calcareous corners of the west.
Sampling 80 sites in counties Limerick, Clare and Galway and one on Mayo’s Clare Island, the team found 14 ant species (two short of Ireland’s known total), up to half a dozen in pastures, bogs and rough grazing and, happiest of all, like so much else, in the warmth and good drainage of the untouched limestone pavement of the Burren.
Michael Viney’s Reflections on Another Life, a selection of columns from the past four decades, is available from irishtimes.com/irishtimesbooks