Elevated levels of carbon dioxide predicted by models of climate change can drive increased production of fungal spores, including some associated with allergies and asthma, according to a new study in Environmental Health Perspectives.

Plant species have different responses to CO2 at concentrations higher than current levels, but one common response when more CO2 is available is that plants often produce more living material (biomass); that is, they grow larger. The ratio of carbon to nitrogen (C:N) in their leaves also often increases. The C:N ratio reflects changes in the plants’ relative production of carbohydrates, which are rich in carbon, and of proteins, which are rich in nitrogen. So a change in a plant’s C:N ratio also means a change in the nutritional intake of any organism (such as A. alternata) that feeds on that plant.

Scientists have known that increasing levels of atmospheric CO2 can lead to increased production of plant pollen grains associated with allergy. Like pollen, fungal spores can trigger asthma and allergic symptoms. Alternaria alternata, a common fungus found on living and dead plants, in soils, and on food, is one spore producer known to trigger allergic symptoms. Around the world, nearly 12% of asthma sufferers are sensitive to the fungus, and in some places, including Portland, Oregon, more than twice that many people are affected.

Researchers used controlled conditions to look at how CO2 levels affected biomass production and leaf carbon content of timothy grass, a common plant grown for hay. Then they examined how using those plants as a food source affected spore production by A. alternata. They grew the grass plants from seeds in controlled environment chambers that allowed CO2 levels to vary while light and water conditions cycled much like they do outdoors. For 60 days the grass grew in conditions simulating four different CO2 levels: 19th-century levels, current levels, and two higher levels that the Intergovernmental Panel on Climate Change has predicted may prevail in 2025 and 2040.

Plants grown at higher CO2 levels predicted for 2025 and 2040 showed increased C:N ratios, and plants grown at the highest CO2 level, predicted for 2040, also produced more biomass than those grown at lower levels. When the leaves harvested from these plants were used to support the growth of A. alternata, the fungus produced nearly three times as many spores on grass grown at higher concentrations of CO2, and the spores produced nearly twice as many allergy-related antigens.

More work is needed to show exactly how the changes in the grass exposed to increased CO2 prompted the fungus to produce more spores, but the current study suggests that for allergy and asthma sufferers, exposure to fungal spores may be an increasing problem as atmospher


Citation:Wolf et al., 'Elevated Atmospheric Carbon Dioxide Concentrations Amplify Alternaria alternata Sporulation and Total Antigen Production. Environ Health Perspect', May 2010; doi:10.1289/ehp.0901867