What was done
The authors measured rates of net photosynthesis during a two-week period in June of 2002 "at the end of the spring rains," when midday air temperatures rose above 40°C, in upper sunlit leaves of mature holm oak (Quercus ilex L.) trees growing close to (5 m), and further away from (130 m), a natural CO2-emitting spring near Laiatico (Pisa, Italy), where the trees had experienced lifetime exposure to atmospheric CO2 concentrations of approximately 1500 and 400 ppm, respectively.

What was learned
At the midpoint of the 14-day measurement period, the net photosynthetic rates of the leaves on the trees growing closest to the CO2 spring were approximately 250% greater than those of the leaves on the trees growing 125 meters further away, where the air's CO2 concentration was 1100 ppm less than it was in the vicinity of the trees nearest the spring.

What it means
In the words of the four Italian researchers who conducted the work, "the considerable photosynthetic stimulation at the very high CO2 site suggests no photosynthetic down-regulation over long-term CO2 enrichment." This real-world finding thus demonstrates the truly amazing potential for very large increases in the air's CO2 content to greatly stimulate photosynthesis and significantly enhance the growth and development of earth's plants over the very-long-term.

Clearly, the aerial fertilization effect of atmospheric CO2 enrichment is not a flash-in-the-pan phenomenon. It is here to stay ... and growing bigger by the day.