Changes in Timothy grass (Phleum pratense L.) pollen production and Phl p 5 allergen content in response to future projected concentrations of carbon dioxide and ozone
Plant reproductive output is sensitive to changing global climate conditions. Increased allocation to pollen production has been observed in certain species and may have important ecological implications. Additionally, increased pollen output by allergenic taxa can have a large impact on human health. Grasses, which have highly allergenic pollen, are widely distributed across the globe. Allergenic pollen in other taxa has been shown to increase under scenarios of warming and elevated CO2, but changes in production and allergen content of grass pollen have not been specifically investigated. We tested the effects of elevated carbon dioxide and ozone on pollen and allergen production of Timothy grass (Phleum pratense L.). Plants were fumigated in eight chambers set up in randomized complete block design, repeated through time, using two concentrations of ozone (O3; 30 and 80 ppb) and carbon dioxide (CO2; 400 and 800 ppm) to simulate present and future projected levels. Pollen was collected in polyethylene bags placed around flowers at emergence and held open with wire to allow airflow. Bag and flower spike were removed after dehiscence. Pollen was counted using a hemocytometer, and the concentration of the Phl p 5 protein, the main allergenic protein in this species, determined through ELISA.
We found that elevated CO2 (800 ppm) significantly increased the amount of pollen produced per flower regardless of O3 level. In addition, the amount of Phl p 5 allergen per flower was significantly increased in plants grown at elevated CO2 and low O3 (30 ppb) conditions. We also found that plants grown in both elevated CO2 and elevated O3 (80 ppb) increased the amount of pollen produced per weight of flower. The Phl p 5 allergen content per pollen grain was significantly reduced by elevated O3, as was flower length and weight. However, this was partially ameliorated by elevated CO2. We conclude that increasing levels of CO2 will cause a 2.5 times increase in Timothy grass pollen production thus increasing human airborne pollen exposure. Ozone impacts human health negatively through irritation of the mucus membranes. It is unlikely that reduced Phl p 5 content would be a benefit for allergy suffers due the increased amount of pollen produced and the interaction with high levels of ozone in the respiratory system. If Timothy grass is a good model for other grasses, this portends for increased allergy suffering worldwide and an important health impact of global climate change.