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

At present, there is substantive evidence that the nutritional content of
agriculturally important food crops will decrease in response to rising
levels of atmospheric carbon dioxide, Ca. However, whether Ca-induced
declines in nutritional quality are also occurring for pollinator food
sources is unknown. Flowering late in the season, goldenrod (Solidago
spp.) pollen is a widely available autumnal food source commonly
acknowledged by apiarists to be essential to native bee (e.g. Bombus spp.)
and honeybee (Apis mellifera) health and winter survival. Using floral
collections obtained from the Smithsonian Natural History Museum, we
quantified Ca-induced temporal changes in pollen protein concentration of
Canada goldenrod (Solidago canadensis), the most widespread Solidago
taxon, from hundreds of samples collected throughout the USA and southern
Canada over the period 1842–2014 (i.e. a Ca from approx. 280 to 398 ppm).
In addition, we conducted a 2 year in situ trial of S. canadensis
populations grown along a continuous Ca gradient from approximately 280 to
500 ppm. The historical data indicated a strong significant correlation
between recent increases in Ca and reductions in pollen protein
concentration (r2 = 0.81). Experimental data confirmed this decrease in
pollen protein concentration, and indicated that it would be ongoing as Ca
continues to rise in the near term, i.e. to 500 ppm (r2 = 0.88). While
additional data are needed to quantify the subsequent effects of reduced
protein concentration for Canada goldenrod on bee health and population
stability, these results are the first to indicate that increasing Ca can
reduce protein content of a floral pollen source widely used by North
American bees.