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Scientists Find Excess Nitrogen Favors Plants That Respond Poorly to Rising CO2As atmospheric carbon dioxide levels rise, so does the pressure on the plant kingdom. The hope among policymakers, scientists and concerned citizens is that plants will absorb some of the extra CO2 and mitigate the impacts of climate change. For a few decades now, researchers have hypothesized about one major roadblock: nitrogen.
Plants build their tissue primarily with the CO2 they take up from the atmosphere. The more they get, the faster they tend to grow—a phenomenon known as the “CO2 fertilization effect.” However, plants that photosynthesize greater amounts of CO2 will also need higher doses of other key building blocks, especially nitrogen. The general consensus has been that if plants get more nitrogen, there will be a larger CO2 fertilization effect. Not necessarily so, says a new paper published in the July 1 issue of Nature.
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If you’re looking for a good conversation about science, history or life – talk to Bert Drake. He’s a plant physiologist and renaissance man who’s been with the Smithsonian Environmental Research Center for nearly four decades. Drake retired in January, but will continue his investigations as an emeritus scientist. We caught up with him before he took well-deserved vacation.
How did you earn a living before you became a scientist?
I was a drummer in a jazz band, a ski guide, the host of a jazz radio program and a high school science teacher.
How did you get drawn to the world of plant physiology?
Nature has always fascinated me and science is about discovering how nature works. I grew up in northern Maine. My father was a barber, but loved the outdoors. I was outside year-round: skiing, canoeing, trapping animals, fishing and taking photos. I knew I wanted to do something connected with biology. I became a science teacher, but it wasn’t until I attended a summer course in ecology that I wanted to get inside a lab and practice science.
In science you almost always get an approximation of an answer because an experiment is only an approximation of reality.
Using forecasts of atmospheric carbon dioxide production for the coming century, the scientists predict the water of the Bay will see rising levels of dissolved carbon dioxide and higher water temperatures. As a result, climate change is expected to worsen problems of low dissolved oxygen concentrations in the Chesapeake’s water and cause sea levels to rise.
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Pat Megonigal is a biogeochemist here at the Smithsonian Environmental Research Center (SERC). The following is an interview with him about his recent research.
Climate change scenarios are driven largely by greater concentrations of carbon dioxide in the atmosphere. One common narrative includes faster-rising seas and the potential drowning of coastal regions. You recently published a paper in the Proceedings of the National Academy of Sciences that gives hope to some coastal wetlands. Tell us what you found.
PM: We conducted a study for two years on the Kirkpatrick Marsh, here on the Chesapeake Bay. We discovered that higher levels of atmospheric CO2 actually stimulated the surface elevation of saltwater marshes. The additional CO2 caused them to basically pop up, or rise in elevation, because the plants developed more roots. It’s kind of a silver-lining story.
How did you simulate climate change?
PM: We put out clear open-top chambers that are about two yards in diameter. They allow us to manipulate the atmosphere around a chunk of marsh. Then, in some of the chambers, we pumped in extra CO2; we raised it to a level that will be roughly what the whole world will be exposed to at the end of the century. And then we measured the changes in the soil’s elevation throughout the growing season.
When you think of measuring elevation, mountains come to mind, not soil. How did you measure the soil’s height?
PM: Well, we needed a stable point of elevation reference, so first we drove a steel rod about 20 feet into the ground. Then came the hard part. We had to design a tool that would give us not only precise, but multiple measurements of the soil elevation – both in and outside of our chambers. We came up with an instrument we dubbed the “monster arm.”
The monster arm?
PM: The technical name is “surface elevation table.” Basically it’s a long metal bar with 90 fiberglass pins running perpendicular through it. It looks like a big comb, but instead of the teeth being fixed in place, they can move up and down. So by gently placing the monster arm across the chambers we could measure where the top of each pin was in relation to the main crossbar. So if a pin rose 100 millimeters above the bar in April and in August it rose 102 millimeters, the soil elevation increased by two millimeters.
Your study showed that the marsh receiving the extra CO2 rose by an additional 3mm a year. Is that enough to keep pace with the rising sea level?
PM: It should help for a while, but we don’t know how much sea level rise a marsh can handle before it will disappear. We do know that rising sea level is one reason that some marshes in mid-Atlantic and around the world are disappearing right now. Our research indicates that some of these wetlands literally have an organic ability to fight back by building new soil. This is especially true for wetlands with brackish water, like Kirkpatrick Marsh. Saltier coastal wetlands won’t be able to accumulate as much soil because their plants are different and don’t respond to CO2 in the same way. But we’re now conducting a new experiment to look at sea-level rise and its effect on soil elevation. We think the pop-up effect we’ve observed will be even more pronounced when the water level rises. We’ll see!
Whigham, along with colleagues Aat Barendregt from Utrecht University and Andy Baldwin from the University of Maryland, has edited the new book Tidal Freshwater Wetlands. It’s a weighty work containing more than 20 chapters written by more than 40 authors. For the first time ever, they have systematically peeled back the layers of these overlooked coastal ecosystems. The book explores how these wetlands work, the animal and plant life they support, and the threats they face.
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In the world of unassuming marshes, the Kirkpatrick Marsh stands apart. Smithsonian plant physiologist Bert Drake has studied this wetland for more than two decades. It’s located in Maryland, along the Rhode River, a sub-estuary of the Chesapeake Bay. Drake and his colleagues have used this community of grasses and sedges to explore whether plants have the potential to become a carbon source or a carbon sink. Watch the audio slideshow below, for a tour of the field experiment.
You can read more about Drake’s experiment on the Smithsonian Environmental Research Center’s Web site.
Q&A with David Gonzalez, 2009 Summer Intern
Major: Evolution, Ecology and Biodiversity
School: University of California-Davis, Class of 2011
What drew you to the Smithsonian Environmental Research Center?
The big-picture research that the scientists do here interested me, particularly the experiments relating to global climate change. Among other things, scientists of my generation are going to have to understand how climate change will impact organisms. We talk about it a lot in my classes, so it was cool to have the opportunity to have hands-on experience exploring some of these issues as an undergrad.
You were here for ten weeks. What was your research project about?
I worked on a global change project that examined the relationship between microbes in the soil and Common Reed, or Phragmites australis. Through a process called methanogenesis, the microbes produce methane, a powerful greenhouse gas, which the plants help to emit into the atmosphere. Because Phragmites australis is found in wetlands worldwide, it’s important to look at how its methanogenesis rates might be affected by global change. Basically we wanted to see if rising CO2 and nitrogen levels exacerbate the problem of methane emissions. So I spent the summer growing Phragmites australis under conditions of elevated CO2 and nitrogen and then measured the response of the microbes and plants.
Do you feel like you spent your summer being an active scientist?
Half of the summer I felt like a scientist; the other half I felt like a gardener. There were a lot of day-to-day chores like watering the plants, counting them, giving them fertilizer, and weeding them. I had to make sure these plants grew to the best of their ability in the short time we had to grow them.
So you learned about the challenges and realities of doing science?
A lot of things I learned this summer relate to how many little things go into doing scientific research – from going out and buying fuses for a machine when it broke down, to purchasing nail polish at a drug store so we could take a peel from a leaf to count stomatal density.
What exactly did you do with nail polish?
We used it in some pilot studies. You apply nail polish to the leaf, let it dry, put scotch tape on it, and then pull it off. This creates a kind of caste of the leaf that you can put on a microscope slide so you can examine a leaf’s cellular structure. For instance, we can go through and count the guard cells, which lets us figure stomatal density and helps us understand how the leaf is responding to the treatments we applied.
You were in the biogeochemistry lab. Did you interact much with the other labs at SERC?
Yeah, one of the great things about SERC is that you’re surrounded by scientists with all these different areas of expertise. I got a lot of help from the forest ecology lab; they let me use some of their instruments for measuring leaf area. But we also got to go on lab exchanges. I spent a day on the water with the “Crab Lab;” I helped them catch and tag blue crabs. And then I also spent a number of evenings setting up mouse traps in the forest with a friend who was interning in the Terrestrial Ecology Lab. In general, we were encouraged to find out what the other labs were up to, which I often did just by talking with the other interns.
What are the dorms like?
The Green Village is awesome. It has a kitchen, a common area and feels like a nice cozy dorm.
How much independence did you have?
Usually you put in eight hours of work a day; occasionally you work more. After that though, you’re free. We cooked dinners together in the evenings. Some of the interns had a garden with a behemoth of a basil plant – that made for a great pesto party. And then we spent weekends exploring the East Coast. I saw fireworks in Washington, DC, on the Fourth of July; camped in Shenandoah National Park; and swam in the Atlantic Ocean.
Was it difficult to get around?
A lot of the interns had cars. That was something I was worried about in the beginning, but everybody turned out to be really friendly. If you needed groceries, there were always people going to the grocery store. If you wanted to visit Washington, DC, it was easy to round up people to hit the Smithsonian Museums. The weekend excursions were great.
You’ll graduate in 2011. How do you want to use the knowledge you’ve gained here at SERC?
I’m definitely planning on doing more scientific research – maybe related to climate change, maybe not. Something that I’m very interested in is communicating the importance of environmental science to the general public and to policy makers. I want to be able to convey why it’s important to think about things like climate change, where your food comes from, farming practices, carbon emissions and things like that. That’s sort of my long-term interest – which I hope will go hand-in-hand with my future studies and research experiences.