What was done
The authors grew wheat (Triticum aestivum cv. Minaret) in open-top chambers fumigated with either ambient air or air enriched with an extra 320 ppm of CO2.  On two occasions during the growing season, assessments were made of plant and soil characteristics, as well as total protozoan numbers and numbers of culturable bacteria.

What was learned
The researchers report they "found higher numbers of bacterivorous protozoa in soil under plants grown at elevated CO2 and larger amounts of root-derived substrates in the soil at plant maturity."  They suggest these findings were the result of "increased root growth and rhizodeposition under elevated CO2," which seems quite reasonable in light of the fact that plant dry weight was 30-46% higher in the treatment enriched with CO2.

What it means
The authors note that "protozoan grazing generally enhances carbon and nitrogen mineralization in soil," which typically results in more nitrogen being made available to plants.  This phenomenon, in turn, enables plants to significantly increase their biomass (as was observed in the CO2-enriched plants in this experiment) while not suffering reductions in tissue nitrogen concentration (as was also observed in the CO2-enriched plants in this experiment).  The end result of these linked phenomena is more high-quality wheat production in response to atmospheric CO2 enrichment, which bodes well for the still-expanding human population of the planet in light of the ongoing rise in the air's CO2 content.