What was done
The authors examined intraspecific variation in germination, growth, biomass allocation, and survivorship of red maple (Acer rubrum L., one of the most abundant tree species in eastern North America) in a two-year growth-chamber study conducted at atmospheric CO2 concentrations of 180, 270, 360 and 600 ppm.  In doing so, they report they "used a nested design with seeds collected from 26 maternal families, comprising six populations from three regions of this species' range."

What was learned
Overall, most of the physiological processes studied displayed positive responses to atmospheric CO2 enrichment most of the time.  However, Mohan et al. report that "all levels of relatedness interacted with CO2 to contribute to variation in response."  Specifically, they found that "germination responses to CO2 varied among families and populations, growth responses depended on families and regions of origin, and survivorship responses to CO2 were particularly affected by regional identities."

What it means
In drawing general conclusions from their many diverse findings, the authors state that "red maple typically germinates better and grows larger with increasing atmospheric CO2."  They also state that "genetic variation in CO2 responses and the rapid increase in global CO2 concentration suggest the potential for adaptive evolution of this species, which may further [our italics] enhance productivity with CO2 enrichment."  Or as they describe it in another place, "this species may evolve in response to globally rising CO2 so as to increase productivity above that experimentally observed today."  Consequently, the ongoing rise in the air's CO2 content bodes well indeed for the future robustness of the planet's red maple trees.