What was done
The authors enriched the air above plots of a nutrient-poor species-rich calcareous grassland in northwestern Switzerland with an extra 240 ppm of CO2 via a set of novel windscreens that "operated around the clock" except during mid-winter (December-February).

What was learned
Among a number of other findings, the authors report that during the six years of their experiment, above-ground plant biomass accumulation increased in response to CO2 by an average of 21%.  Simultaneously, there was an increase in soil moisture due to CO2-induced reductions in plant transpiration.  They also report that microbial nitrogen (N) pools did not change, "indicating that elevated CO2 did not stimulate net microbial immobilization of N which could have imposed a negative feedback on plant growth [but didn't]."

What it means
As the air's CO2 content continues to climb ever higher, there is a good likelihood the productivity of earth's grasslands, even in nutrient-poor areas, will steadily and consistently increase their productivity, even in areas that may experience slight decreases in precipitation.