Every backyard gardener knows that earthworms are good for the soil. They chew and churn through organic material, aerating the soil and leaving nutrient-rich castings behind. But the common night crawlers you see on the sidewalk after a rain are not native to North America and, like many invasive species, are doing more harm than good in some ecosystems. This is particularly true for the forest floor that is home to native wild orchids. In a recent conversation with the Torch, Dr. Melissa McCormick of the Smithsonian Environmental Research Center in Edgewater, Md., talked about her work with earthworms, explained why orchids are the “pandas of the plant world” and encouraged young scientists to find what they love and stick with it.
Let’s start with the basics: How long have you been with the Smithsonian?
I came to the Smithsonian in 1999 as a post-doc to study interactions between orchids and fungi with Dennis Whigham. I did my doctoral research at Michigan State University in ecology and evolutionary biology and behavior. I’ve always been interested in how organisms interact with their environment and with each other.
I can credit a lot of that interest to spending so much time outside as a kid. We went hiking in the mountains on family vacations and my mother was an avid gardener (and later a Master Gardener). I was interested in plants because she always had all kinds of different flowers around the yard. I’ve been digging in the dirt from an early age!
Any gardener just assumes that earthworms come with the territory if you have good soil. I had no clue they were an invasive species!
I had no clue either until I talked to Katalin Szlavecz of Johns Hopkins University, who studies soil invertebrates. Earthworms are great for the garden because they aerate the soil, turn it up, and make it a great environment for garden plants to grow, but it turns out most of the earthworms we know and love are not native. We do have some native species of earthworms at SERC but we’re pretty close to northern extent (along the east coast) of most native earthworms. I would venture to say that nearly 100 percent of the worms that you find in your yard or your garden are not native. They were probably were introduced initially by European settlers, including those at Jamestown, who brought plants with them that would have had earthworms in the soil around their roots. Also, ships used soil as dry ballast then and there would have been earthworms in the ballast that was dumped.
National Geographic published an interesting article in 2007: The front cover is a drawing of a Native American from the time of the Jamestown settlement and the title is Jamestown, the Real Story: How Settlers Destroyed a Native Empire and Changed the Landscape from the Ground Up. One of the take-home messages is that the soil organisms, particularly the earthworms that were brought over by the settlers, dramatically changed the forest environment and thus changed the plants that grew there and, in many cases, affected the plants that the Native Americans would have depended on.
Specifically, the recent study published in Annals of Botany Plants (with intern Kenneth Parker, Dennis Whigham of SERC, and Katalin Szlavecz of Johns Hopkins) looks at how native orchids are affected. Orchids rely on fungi in the soil in order to germinate and access nutrients. How are the earthworms interfering with that relationship?
Well, the first thing they do, of course, is eat the seeds. Earthworms don’t really seek out orchid seeds but the seeds are very, very small and are eaten as a consequence of the worms eating the soil and the leaf litter that the seeds happen to have fallen on. About 70 percent of the seeds that the worms eat become unable to germinate after they pass through the earthworm’s gut. Of the ones that can still germinate, a big chunk of those end up buried too deeply for the fungi to be able to reach them. The fungi that many orchids in our area depend on are in the surface layers of the soil—they’re in the leaf litter and the top layer of soil that’s in contact with the leaf litter. Orchid seeds consumed by earthworms are often defecated too deep in the soil to come in contact with the fungi they need to grow.
Are orchids as delicate as they appear? Are they becoming endangered?
Orchids themselves aren’t necessarily delicate, but they very closely reflect the health of an ecosystem. Because they are dependent on particular fungi that grow in the soil under particular conditions, they’re picky about where they grow. An ecosystem that is not healthy, that doesn’t have the full complement of fungal species that it normally would—maybe it has been invaded by other species or the soil has been turned up—will not support orchids very well. It is true that many of our native orchids are declining, some precipitously. However, that said, orchids are the most species-rich plant family on earth. They grow everywhere, from the tropics to very close to the Arctic Circle.
I bet most people don’t know that.
Orchids are extremely diverse and they’re extremely widespread. There are orchids in Alaska, there are certainly orchids here in Maryland, and there are even orchids on some of the Antarctic islands. In some cases an extremely disturbed environment could be good for a particular orchid species. A friend of mine is working on orchids that grow on mine spoils in Estonia and they do really well there! [Ed. Spoils are the rock, soil and other debris dug up and cast aside in the course of mining operations.] It’s got to be just the right combination of conditions that, for whatever fluke reason, happens to promote the growth of a particular orchid. Here in Maryland, we are seeing a decline in native orchids that would normally be growing in relatively good woodland and prairie conditions. Those are the types of habitats that are being lost and degraded.
Those woodland and prairie habitats are being lost for many species, in addition to orchids.
It’s true that the loss of woodlands and prairies is significant for many species; orchids are one visible and charismatic indicator of that loss. We sometimes call orchids “the pandas of the plant world” because they’re beautiful, well-liked, interesting, and can be used as a bellwether for the health of an ecosystem. So, if you see orchids starting to disappear, they’re probably just the first of many species that will vanish.
What other projects are you involved in?
In addition to working with orchids, I also work with wetland species, invasive plant species and understanding how and why plant species invade some areas and not others. I’m also working with how earthworms impact the fungal community—not only from the perspective of orchids but from the perspective of tree seedlings. A lot of people don’t realize that something like 90 percent of land plants depend on associations with fungi in order to get access to nutrients and water in the soil. I’m involved with the BiodiversiTree project [to plant a forest that will be studied for the effects of climate change over the course of a century] and prompted the design to include the different types of microbial associations among the trees there.
Do you have any advice for young women interested in science?
There are plenty of opportunities in science for women. Don’t let anyone tell you otherwise! I personally have never experienced, (at least, to my knowledge!) any kind of discrimination because of my gender. It’s always good to be tough-minded—science is not an easy field for anybody and it’s always hard to be able to balance family and work. That’s true in any field and it’s going to be true whether you’re a man or a woman. Find what you love, what you find interesting and stick with it. The great thing about science is you get to ask your own questions and you get to keep going in the directions you think are interesting.
Posted: 18 April 2013