Global Climate Change Impacts in the United States 2009 Report Legacy site

Although environmental factors such as precipitation and temperature are recognized as influencing pollen production, the impact of rising atmospheric carbon dioxide concentration ([ CO2]) on the potential growth and pollen production of hay- fever- inducing plants is unknown. Here we present measurements of growth and pollen production of common ragweed (Ambrosia artemisiifolia L.) from pre- industrial [CO2] (280 mu mol mol(-1)) to current concentrations (370 mu mol mol(-1)) to a projected 21st century concentration (600 mu mol mol(-1)). We found that exposure to current and elevated [CO2] increased ragweed pollen production by 131 and 320%, respectively, compared to plants grown at pre- industrial [CO2]. The observed stimulations of pollen production from the pre- industrial [CO2] were due to an increase in the number (at 370 mu mol mol(-1)) and number and size (at 600 mu mol mol(-1)) of floral spikes. Overall, floral weight as a percentage of total plant weight decreased (from 21% to 13%), while investment in pollen increased (from 3.6 to 6%) between 280 and 600 mu mol mol(-1) CO2. Our results suggest that the continuing increase in atmospheric [CO2] could directly influence public health by stimulating the growth and pollen production of allergy- inducing species such as ragweed.