The zoo beneath our feet
Plants manufacture carbohydrates through photosynthesis, but not just for themselves. They release some of their carbon sugars into the soil, which causes the bacteria and fungi to show up to feed.
The bacteria crowd around the root zone, and the fungi form vast networks of interlocking strands that often link one plant to another. The bacteria convert nitrogen and other nutrients into forms the plants can use, often by getting devoured by other microbes.
The fungal strands, the mycelium, effectively increase the root mass of its host plant by as much as a 1000 times and transport a bevy of goodies to the host plants, including phosphorus, copper, calcium and zinc. There is also evidence that trees use this network to send signals to one another if, say, leaf-eating pests have arrived.
In his Ted Talk, mycologist Paul Stamets referred to mycelium as ‘‘Earth’s natural internet’’.
Although some plant (and human) diseases are caused by soil-borne fungi and bacteria, most of these microbes are beneficial and keep the bad ones in check. The organisms assist in other ways, by increasing the size of soil particles, which improves the ability of the soil to hold water and air.
Even in the middle of a city, the subterranean world is thriving.
Scientists took almost 600 soil samples from across New York’s Central Park and discovered a surprising diversity and richness. They identified more than 120,000 types of bacteria and more than 40,000 species of fungi, protozoa and arthropods.
Among the unexpected findings: The microbial species were the same, more or less, as those found in parts of the world with dramatically different flora and climates from New York’s, including Antarctic cold deserts near Scott Base, tropical forests and grasslands.
There was a strong association between the diverse organisms in each sample. ‘‘Unravelling these relationships will be critical to building a more integrated understanding of below-ground ecology,’’ the researchers wrote in a paper published by the journal for the British Royal Society. ‘‘Our work highlights that most of the diversity found in soil remains undescribed.’’
Enough is known, however, to create a 21st century subset of farming known as regenerative agriculture. The farmers have discovered that if you foster this biosphere, you don’t need expensive fertilisers because the microbes repay the plants with nutrients. They also, for obvious reasons, avoid pesticides that would kill this soil life.
The farmers do as little soil digging as possible because traditional tillage destroys the fungal networks and the desirable
Some gardeners turn to compost tea to build soil microbes. This is made by aerating sugars, compost and humic acids in nonchlorinated water and then spraying the brew on plants and soil.
Others are not convinced that this is needed, though everyone agrees that the way to foster the soil food web is to top-dress growing beds and lawns with organic matter such as shredded leaves or finished compost.
James Nardi, a biologist at the University of Illinois, offers this advice: ‘‘Work with your fellow non-human gardeners. I never use synthetic fertilisers, and I never use pesticides.’’
In the autumn, he mixes horse manure with fallen leaves, shreds the mixture and applies it as a mulch to his growing beds. ‘‘In the spring, I have this lovely, spongy soil,’’ he said. Lowenfels shreds autumn leaves on his lawn and lets the biosphere use them over the winter.
The organic gardener’s mantra has never seemed more appropriate. Feed the soil, not the plant. – Washington Post