What was done
The authors collected seed from Bromus erectus plants growing in a field experiment utilizing atmospheric CO2 concentrations of 360 and 650 ppm.  Seeds produced at each atmospheric CO2 concentration were then germinated at each of the CO2 levels, and the resulting seedlings were allowed to develop.  Thus, the authors studied the effects of elevated CO2 on seed characteristics and subsequent seedling development for this important perennial grass, which is common to the nutrient-poor calcareous grasslands of Europe.

What was learned
Elevated CO2 increased individual seed mass by about 9%.  In addition, plants exposed to 650 ppm CO2 produced seeds that had a carbon to nitrogen ratio that was almost 10% greater than the carbon to nitrogen ratio of seeds produced by plants fumigated with ambient air.  However, these CO2-induced effects on seed characteristics had little to do with subsequent seedling growth.  In fact, when seeds produced from ambient or CO2-enriched parent plants were germinated and grown at ambient CO2 concentrations, there were no significant differences in the seedling size of the two groups of plants after 19 days of treatment.  Similarly, when seeds produced from ambient or CO2-enriched parent plants were germinated and grown at elevated CO2 concentrations, the resulting seedlings of each group were also not significantly different from each other in size.  However, the CO2-enriched seedlings produced from both types of seeds were almost 20% larger in size than seedlings grown at ambient CO2 concentrations, demonstrating that the direct effects of elevated CO2 on seedling growth were more important than the differences in seed characteristics produced by the effects of atmospheric CO2 enrichment on the plants that produced the seeds.

What it means
As the air's CO2 content increases, it is likely that Bromus erectus grass will display increases in growth that are more directly related to the effects of elevated CO2 on "real-time" physiology than any effects atmospheric CO2 enrichment in the preceding generation may have had on the plants that produced the seeds from which the plants of the present developed.