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Ragweed and Pollen Study
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Will Microclimate differences between cities and the surrounding countryside affect the ability of ragweed to grow and produce pollen? We know that ragweed pollen production is sensitive to rising atmospheric CO2. Work within controlled environment chambers at USDA's Climate Stress Lab has shown that the CO2 concentration from the turn of the century (~280 ppm) results in ~5 grams of pollen per plant under optimal conditions. However, the amount of pollen doubles to 10 grams when ragweed is exposed to current CO2 conditions, and doubles again for projected increases in atmospheric CO2 of 600 ppm.

We also know that cities are heat sinks as well as sources of CO2. Weather stations were set up at: 1) an organic farm in Buckeystown, MD, 2) The Carrie Murray Nature Center in Baltimore, 3) Towson University and the 4) The Maryland Science Center, located in Baltimore's Inner Harbor.

At each station a record of weather (TEMP, RH, PAR, CO2) is being kept and a small plot of common ragweed is being maintained. Our goal is to determine if existing climatic differences can contribute to ragweed growth and pollen production.

Of course there is less ragweed in the city, however recent
reports indicate that exposure to tropospheric ozone and diesel fumes can increase your sensitivity to ragweed pollen seven fold. So even though there is less pollen, it has an overall greater effectiveness.

This study has been completed (October, 2001). Please contact Lewis Ziska for more

Lewis Ziska, USDA, Alternate Crops and Systems Laboratory