New Notions About Who Are Good Guys vs. the Bad Guys
Release Date: 02-12-2010
Ask a farmer or gardener about nematodes, and you will likely hear tales of two types: bad and worse. Bad are the legions of nematodes that topple plants by attacking roots or acting as vectors for diseases. Various nematodes infest nearly every kind of fruit, vegetable, tree and turf, causing untold damage and loss. Worse are those commonly called roundworms that infect livestock, pets and even people.
Conversely, if nematodes get a bad rap, their neighbors, earthworms, are extolled as architects of the underground. Tunneling to aerate and drain soil and bring subsoil to the surface, they chomp through detritus, turn it into rich humus and leave behind castings valued for their high fertility. Earthworms were the darlings of Darwin and are the Vita-Mix of vermiculturists.
Now two University of Vermont research scientists are turning traditional thinking on its ear. Deborah Neher and Josef Gorres, plant and soil science faculty members, tease out the truth about life in the thin universe that lies between sky and bedrock: topsoil, leaf litter and earth's teeming surface. Their findings demonstrate that a sustainable ecosystem is one of delicate balance, of species indicators that signal the overall health of the soil and of the communities of small animals that may turn out to be linchpins of the food web.
Neher Knows Nematodes
When it comes to nematodes, we don't know even half the story. It is likely we identified those nematodes that are pests and a few that are beneficial and overlooked the rest.
"This is the last frontier — we know more about outer space and the deep sea than we know about the organisms in our own back yard," Neher says. "Soil animals make up 23 percent of the total diversity of life, yet we know only about 10 percent of the species and little about their ecology. Not only are there many gaps in the taxonomy, only a handful of scientists study what is known." It's not enough to discover and name these ubiquitous albeit barely visible creatures: nematodes and their kin — mites and springtails — that live by the thousands to millions per square foot of soil. Over the past 20 years, Neher has just begun to tease out their significant role in the ecosystem.
One of her early discoveries is "that physical disturbances, such as cultivation, have a more detrimental effect on soil food webs than chemical disturbances, such as fertilization or pesticides," she explained.
"I think there's a lot these soil communities could do for us, but we have no idea what they could do, because we feed them fertilizer which makes them lazy, or we chop them up with the tiller," Neher observes.
So Neher backed up to move forward. She narrowed her focus to a more undisturbed ecosystem — woodlands — where she identifies soil animals and how they function. Smack dab in the middle of the food web, microinvertebrates are "a keystone link" between predators and herbivores above ground and bacteria and microbes below ground, she says. By measuring how well they predict the quantity of nitrates and ammonium in soil and whether they regulate populations of microbes that decompose lignin or cellulose, Neher found that nematodes are an indicator of soil health in the forest floor.
"Microinvertebrates integrate biological, physical and chemical properties to tell us if the soils are providing the ecosystem services that we expect," says Neher. This includes the all-important processes of nutrient cycling and decomposition. "We need decomposition to recycle nutrients, however, we don't want such fast decomposition that we lose all the carbon to the atmosphere."
Gorres' New Angle on Worms
Nutrient recycling and fast decomposition are what earthworms are all about.
Josef Gorres is seeing first hand that where worms congregate in the forest, "there is no leaf litter, no organic layer and not as much pore space," he says. As a result, "the surface seed bank is exposed to seed predators and harsh weather. This is where small plants germinate, but because the duff is gone, they can't do that. Therefore, there are fewer herbaceous plants."
Besides grinding the woodland carpet and exposing seeds, earthworms leave a different soil — fertile in nitrogen, phosphate and potassium.
"Native plants may not adapt to the fast release of nutrients that earthworms cause," says Gorres. "And one hypothesis is that exotic invasive plants move in instead because they have fewer competitors, bare ground to colonize and maybe the edge over natives that are slower to become active earlier in the spring."
Worms' effects on wildflowers and shrubs are documented, but Gorres is interested in the long-term change of the forest canopy. "I'm also interested in how earthworms change the chemistry of soil in production maple forests, because that could change the flavor of syrup and the color of the foliage," he says. "That part is speculative, but no one has looked at that."
Laying bare the forest floor is fairly new in the East's natural history. Colonists brought Lumbricus terrestris to the Americas on rootstocks and in ship ballast; over time these all but replaced native earthworm populations and spread to wormless areas. Gorres estimates about 15-20 invasive earthworm species in the Northeast. Normally populations spread slowly; nowadays, worms are introduced by construction, with plants, when gardeners purchase red wigglers and by fishermen who dump bait.
While people are well aware of devastating invasive forest insects such as emerald ash borer and hemlock wooly adelgid heading toward Vermont, here's a surprise.
"A relatively new worm called "crazy snakeworm" was first discovered in the 1990s in nine commercial greenhouses in New York City. It is many times more voracious than other earthworms," says Gorres.
He's identified one as well — in 2008 — in a patch of ferns at the woodland edge of UVM's own Horticultural Research Farm.
CAPTION: Josef Gorres, left, studies earthworms while Deborah Neher researches the microscopic nematodes in forest duff. Both scientists are adding new information on how small creatures effect woodland ecosystems in extensive ways. ~Cheryl Dorschner photo.