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The Role of Fungi in the Production of Biogenic Aerosols
Elbert, W., Taylor, P.E., Andreae, M.O. and Poschl, U. 2007. Contribution of fungi to primary biogenic aerosols in the atmosphere: wet and dry discharged spores, carbohydrates, and inorganic ions. Atmospheric Chemistry and Physics 7: 4569-4588.

Citing multiple references as authority for their statements, the authors note that primary biogenic aerosols (PBA) are "ubiquitous over land and oceans," can "influence the Earth's energy budget by scattering and absorbing radiation," and can "initiate the formation of clouds and precipitation as cloud condensation and ice nuclei."

What was done
Focusing on actively-wet-spore-discharging Ascomycota (AAM) and actively-wet-spore-discharging Basidiomycota (ABM), Elbert et al. "address the active (forcible) discharge of fungal spores, which is accompanied by the emission of aqueous droplets containing carbohydrates and inorganic ions, ... summarize the information on the atmospheric abundance of wet and dry discharged fungal spores that is available from earlier scientific studies made at various locations around the world, ... and present new measurement results and budget calculations for aerosol samples from tropical rainforests in Amazonia."

What was learned
The four researchers confirmed that AAM and ABM are major sources of PBA, finding from their own work that "in pristine tropical rainforest air, fungal spores indeed account for a major fraction of coarse particulate matter (up to ~45%)." They also calculate that the emission rate of total fungal spores (~50 Tg yr-1) "is of similar magnitude as current estimates of the rates of emission and formation of other types of continental air particulate matter (primary and secondary organic aerosols)."

What it means
Of particular interest within the context of rising near-surface air temperatures and atmospheric CO2 concentrations, Elbert et al. write that "global warming and increasing CO2 concentrations may enhance the spread of fungi and emission of fungal spores," citing the works of Klironomos et al. (1997), Hoye et al. (2007) and Raupach et al. (2007), while further concluding that "an increase of fungal spores acting as cloud condensation and ice nuclei may influence the hydrological cycle and provide either positive or negative feedbacks to climate change." We would only add, in this regard, that the evidence for negative feedbacks of this nature far outweighs the evidence for positive feedbacks (see the many items archived under Climate Change (Feedback Factors - Biophysical) in our Subject Index). This most recent example of a hitherto unappreciated biological phenomenon thus provides yet another example of how various life-forms act to maintain earth's near-surface air temperature within bounds conducive to their own continued existence.

Hoye, T.T., Post, E., Meltofte, H., Schmidt, N.M. and Forchhammer, M.C. 2007. Rapid advancement of spring in the High Arctic. Current Biology 17: R449-R451.

Klironomos, J.N., Rillig, M.C., Allen, M.F., Zak, D.R., Pregitzer, K.S. and Kubiske, M.E. 1997. Increased levels of airborne fungal spores in response to Populus tremuloides grown under elevated atmospheric CO2. Canadian Journal of Botany 75: 1670-1673.

Raupach, M.R., Marland, G., Ciais, P., Le Quere, C., Canadell, J.G., Klepper, G. and Field, C.B. 2007. Global and regional drivers of accelerating CO2 emissions. Proceedings of the National Academy of Sciences, USA 104: 10,288-10,293.

Reviewed 12 December 2007