What was done
In several related experiments, the authors grew tobacco (Nicotiana tabacum L.) plants from germination in controlled-environment chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm to study the effects of elevated CO2 on the activity of nitrate reductase, which is a key enzyme involved in making valuable nitrate-nitrogen available to plants.

What was learned
From their several experiments, the authors learned that atmospheric CO2 enrichment markedly increased nitrate reductase activity in young, but not old, tobacco plants, presumably because growth rates were much greater in the younger plants and they needed the extra nitrogen provided by this phenomenon to maintain their heightened level of development.  In one experiment, in fact, the authors reported a 2-fold increase in nitrate reductase activity in leaves exposed to elevated CO2, while in another experiment they observed a 2-fold increase in nitrate reductase activity in roots.  What is more, these nitrate reductase activity increases led to shoot and root biomass production rates that were, respectively, 2- and 3-fold greater in CO2-enriched air than in ambient air.

What it means
As the air's CO2 content continues to rise, the nitrate reductase activity of tobacco plants (and perhaps that of other of earth's plants) will likely rise right along with it, thereby making greater amounts of nitrogen available to support CO2-enhanced rates of growth and biomass production.  And this phenomenon should increase the mean global rate of terrestrial carbon sequestration.