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Title: Rising atmospheric CO2 is reducing the protein concentration of a floral pollen source essential for North American bees

item Ziska, Lewis
item Pettis, Jeffery
item Tomecek, Martha
item CLARK, ANDREW - Smithsonian Institute
item DUKES, JEFFREY - Purdue University
item LOLADZE, IRAKLI - University Of Maryland
item Polley, Wayne

Submitted to: Proceedings of the Royal Society B
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2016
Publication Date: 4/23/2016
Citation: Ziska, L.H., Pettis, J.S., Tomecek, M.B., Clark, A., Dukes, J.S., Loladze, I., Polley, H.W. 2016. Rising atmospheric CO2 is reducing the protein concentration of a floral pollen source essential for North American bees. Proceedings of the Royal Society B. 283(1828):20160414.

Interpretive Summary: Bees are important in agriculture as pollinators. Recently, honeybees are starting to disappear. The reasons for this are unclear. One possibility is related to poor nutrition. To investigate this possibility, scientists from USDA, Purdue University, the University of Maryland and the Smithsonian Institution looked at whether rising atmospheric carbon dioxide (CO2) could be influencing pollen quality. Researchers examined historical pollen records for goldenrod, a flowering plant that provides much of the pollen for bees before they over-winter. In addition, researchers conducted field trials that grew goldenrod at different CO2 concentrations. Both studies showed that rising CO2 has reduced the protein concentration of goldenrod pollen by 25%. The reduction in pollen protein concentration by rising CO2 levels may be influencing bee nutrition in a bad way.

Technical Abstract: Qualitative changes in floral pollen protein have been shown to be an important aspect of pollinator health. Flowering late in the season, goldenrod (Solidago spp.), provides an essential autumnal source of floral pollen for wild bee and honeybee populations prior to winter, with tall or Canada goldenrod (S. canadensis) being the most widely distributed in North America. Although rising atmospheric CO2 concentration (Ca) has been shown to reduce nitrogen and protein in plant tissues, the relationship between Ca and protein concentration of floral pollen has not been elucidated. To explore a possible Ca - pollen protein link, we quantified the carbon and nitrogen concentrations of pollen samples from floral collections of S. canadensis housed at the Smithsonian Museum of Natural History. These collections represent S. canadensis populations throughout the United States and southern Canada from the period 1842-1998 (Ca from ~280 to 365 ppmv). In addition to the historical record, we conducted a three year in situ trial of S. canadensis populations grown along a continuous Ca gradient from ~280 to 500 ppmv. Although the absolute values differed, both investigations showed a significant decline (~25% over the Ca range studied) in protein and nitrogen concentrations and accompanying increases in the carbon: nitrogen ratio of S. canadensis pollen associated with rising Ca. These data indicate that rising Ca has reduced, and may continue to reduce, protein concentration for this temporally important pollen source and could, by reducing nutritional quality, represent an additional environmental stressor of honeybee (Apis mellifera) populations.