What was done
Nasturtiums (Tropaeolum majus) were grown from seed and through flowering and senescence (77 days total) in growth chambers receiving atmospheric CO2 concentrations of 380 and 760 ppm to determine the effects of elevated CO2 on vegetative and reproductive growth, as well as on flower characteristics, including numbers, longevity and nectar quantity and quality.

What was learned
Elevated CO2 increased total plant biomass by 35% and root biomass by 78%.  However, it did not affect reproductive biomass, nor did it alter individual flower dry weights.  In addition, atmospheric CO2 enrichment did not affect the time to flowering, flower longevity or the number of flowers produced.  Neither did it delay the onset of senescence.  Elevated CO2 did, however, positively influence the total volume of nectar produced in CO2-enriched flowers, increasing it by 2.4-fold over that produced in ambiently-grown flowers; yet it did not alter the sugar and amino acid characteristics of the nectar.  Thus, atmospheric CO2 enrichment increased plant growth and the quantity of nectar secreted, but not its quality.

What it means
As the CO2 content of the air rises, it is likely that nasturtiums will respond by modestly increasing their overall biomass and dramatically increasing their belowground biomass.  In addition, atmospheric CO2 enrichment should induce a stunning increase in nectar secretion in flowers without altering their sugar and amino acid contents.  Thus, in the future, it is likely that pollination in this flowering species will be facilitated by even greater numbers of the same insects that currently assist in this process, thereby maintaining, and even enhancing, longstanding symbiotic relationships that coevolved over time.