Mitigating Atmospheric Toxins
Stephanie McPherson for TEI
William Manning, Professor of Plant Pathology in the Department of Plant, Soil and Insect Sciences, is not only asking what we can do for nature, but what nature can do for us. For the past thirty years, Manning has been examining the interaction of greenhouse gases and plant matter. “I’m just a natural scientist who wants to know what’s going on out there,” he says. “What does it mean?” Right now, by looking at injury and absorption, Manning is trying to decipher which plants are the best to cleanse the air or act as pollution markers. “If Tree A is better at taking up CO2 than Tree B, let’s use tree A if we can. If Tree Z is better at taking up NO2 than Tree Y, then we should use Z, but those criteria are not used,” Manning says. “So I’m trying to convince people that trees should really do something for us other than just be attractive.”
According to a number of computer models, nitrogen dioxide, a precursor to the air pollutant ozone, should be used by trees as a source of nutrients. If this is true, it would mean the trees are acting as a sort of natural air filter. This would be useful in cities where air pollution from combustion engines is high. Manning and graduate student Tanner Harris, however, are not content to assume the simulations’ validity. Their field work in Springfield deals with monitoring the NO2 uptake of Red Maple and London Pine trees. “We really would like to demonstrate in Springfield whether or not trees are taking up NO2 from the air and, if so, how much?” Manning says. Their focus is Liberty Street - flanked by Routes 291 and 91 and a railroad, it is a prime spot for combustion engine emissions. Manning and Harris use a number of small, inexpensive devices called passive samplers – what looks like a PVC pipe cap hung with the open side down – on each tree they monitor. Clipped inside the plastic is a container with a small piece of filter paper soaked in a nitric form of nitrogen. The NO2 in the air flowing across the filter causes the nitrogen to change from the nitric to the nitrate form. By determining how much has changed, they can figure out how much nitrogen dioxide is present in the air.
Through these methods, they have observed that NO2 levels are higher within the canopy of the trees than outside and that, true to the models, leaves are absorbing some of that NO2. These observations have been confirmed by a laboratory at Cornell University where the leaves are analyzed, confirming the plant uptake of NO2 through detection of the stable isotope N15. “It just happens that the stable isotope form is very characteristic of NO2 from combustion, so it’s almost like a marker, which is really neat,” Manning says. But while they see some NO2 absorption, they don’t know whether or not it is enough. “It’s not clear whether the uptake is really significant, in terms of what’s in the air. I mean, it’s true this may happen, but is it really a way to reduce pollution?” he asks. Manning hopes to extend this research to a wider variety of trees, to see if there are more efficient NO2 absorbers.
Manning is also interested in the effects of daily levels of ozone on the bodies of plants. The more sensitive a plant is to ozone, the greater the injury to the leaves. During the summer, ozone levels in the Pioneer Valley peak in late afternoon. Not much pollution is generated in the Valley itself, so most damaging compounds ride in on the wind from major southern cities. “When the wind blows from a southwesterly direction, which it often is, it’s coming out of metropolitan New York and New Jersey,” Manning says. “It’s moving basically right up through the valley and it’s bringing all the precursors and all the air pollutants with it.” Manning is monitoring this phenomenon in collaboration with the Connecticut Agricultural Experiment Station in New Haven and Valley Laboratory in Windsor Locks. Each contributor grows 18 pots of a certain clover known to be ozone sensitive. Half the crop is treated with EDU, a compound to protect against ozone damage. The crops are then examined throughout the summer to determine how they grow and reproduce while affected by ozone. Data from the three locations is then compared to determine which areas have the highest occurrence of the pollutants. Current data suggests New Haven has the highest presence of ozone, Windsor Locks fares a little better, and Amherst has the clearest air of the three areas sampled.
Though ozone can be harmful, it is part of the natural makeup of our atmosphere. Problems arise when levels get too high. In recent years, thanks to improved abatement in vehicles and stricter clean air laws, ozone levels have been decreasing. “In terms of high episodes, things are much better than they used to be,” Manning says. “But what’s left are the day to day lower episodes, which nobody gets excited about because they’re underneath the standard [the level at which damages occur].” In fact, at these lower levels even just two notches below the standard, ozone stimulates plant growth. Currently, the usual background, or safe level of ozone, during the summer is about 25 to 30 parts per billion. Models predict that in 40 years the average ozone background could be at the current standard.
In another line of research, Albertine and Manning are working in greenhouses to mimic global warming conditions. “All these things are really tied together. You can’t really only study part of the environment and ignore the rest of it,” Manning says. As the world heats, there will be residual warmth overnight, which will then heat the ground and those things growing in it. They have found that plants growing in warmer soil germinate faster, but they also reach ozone sensitivity more quickly and the effects of ozone on the warmed plants are greater than the normally grown group. Albertine is taking this research outside to see how the findings hold up under more real-life circumstances.
Manning wants to give these findings a human application. He hopes to figure out a way to translate the ozone data from the plant experiments into something meaningful for human health. Simply monitoring the ozone through detectors is not enough. If there is no plant injury, there is likely no danger to humans. If the plants are damaged, however, there could be some implications for society. The problem is plants and humans respond differently to different stimuli, meaning what is harmful to a plant may not affect people. “Whether or not clover gets ozone injury is of very little concern to most people,” Manning says. “But if the clover is injured and [the people] are injured, then they’re really quite interested. What we need to pursue is the relationship between plants, pollutants and people. Right now, they’re parallel lines.”
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