A new study of the relationship between carbon dioxide levels and plant growth suggests for the first time that not only do plants grow bigger and produce more pollen when exposed to higher levels of the greenhouse gas, CO2, but the common, allergen-producing fungus Alternaria alternate produces three times more spores when feeding on those enriched plants. The spores disperse on the wind, making allergies and asthma symptoms worse.
Although such well-fed spores may contain less protein per spore, if models of climate disruption and global temperature rise are correct, the overall increase in airway-irritating antigen to which people will be exposed in 2040 will be roughly two times higher than now, according to Christine Rogers, an aerobiologist at the University of Massachusetts Amherst School of Public Health and Health Sciences.
As she explains, "The fungi have an enriched food source and produced three times as many spores, but less protein per spore. Overall, the amount of antigen people are going to be exposed to is roughly twice as high. This is the first time we know of that a study has looked at the level of antigen in fungal spores in response to carbon dioxide."
The research group, including another UMass Amherst researcher, Michael Muilenberg, plus colleagues at the University of Maryland and the USDA Agricultural Research Service, Beltsville, Md., reported these results in the online current edition of the journal Environmental Health Perspectives.
It has been known for some time that increasing levels of CO2 can increase the ability of some plants to grow larger and produce more pollen, making life miserable for people who are allergic to the tiny irritants. The increase in available carbon lets plants produce more carbohydrates and proteins, which serve as additional nutrients for fungi that feed on the plants. Spores from Alternaria, a fungus that lives on plants and in soil, similarly triggers asthma and allergic symptoms. Nearly 12 percent of asthma sufferers are sensitive to this fungus, and in some places the percentage is higher.
For the study, Rogers and colleagues studied how four different CO2 levels in the air, 300, 400, 500 and 600 parts per million (ppm), controlled in environment chambers, affected biomass production and leaf carbon content of timothy grass, a common hay crop.