What was done
The authors divided a 0.5-acre greenhouse located in the center of the Arava Valley in the southern part of Israel into two parts, one of which was exposed to ambient air and one of which was exposed to air that had a CO2 concentration of 1000 ppm throughout the morning, 400 ppm between 1300 and 1500 hours, and then 600 ppm until the next morning.  Under these conditions they grew melons (Cucumis melo); and in the early flowering stage they collected and measured the volume of nectar produced per flower between 0900 and 1530 hours, as well as the sugar concentration of the nectar.

What was learned
Average nectar volumes per flower were significantly higher in the CO2-enriched sector of the greenhouse than in the control sector, sometimes by as much as 100%; and since the sugar concentration of the nectar was the same in both treatments, sugar production per flower was stimulated by an identical amount in the CO2-enriched air.

What it means
The authors note that the only pollinator used in the greenhouse production of melons in Israel is the honey bee (Apis mellifera); and they say that "improvement in nectar reward can increase the attractiveness of the flowers to the bees, increase pollination activity and consequently increase the fruit set and the yield."  Hence, as the air's CO2 concentration continues to rise, or as greenhouse managers implement atmospheric CO2 enrichment techniques, we may expect to see such benefits realized routinely.