What was done
The authors exposed four-year-old Japanese pear trees (Pyrus pyrifolia Nakai) to atmospheric CO2 concentrations of 350, 700 and 1400 ppm for two days to study the short-term effects of elevated CO2 on fruit expansion in this species.

What was learned
Seedlings exposed to 700 and 1400 ppm CO2 exhibited photosynthetic rates that were 90 and 130% greater, respectively, than those displayed by control plants in ambient air.  In addition, stomatal conductances were 18 and 32% lower at 700 and 1400 ppm than they were at the ambient CO2 concentration, respectively.

These physiological changes led to some interesting physical changes in this species.  At the ambient CO2 concentration, seedlings exhibited daytime stem shrinkage and cessation of fruit expansion.  In contrast, seedlings exposed to elevated CO2 exhibited no stem shrinkage and their fruit continued to expand, ultimately leading to enhanced fruit size.

What it means
As the air's CO2 concentration continues to increase, Japanese pear seedlings likely will exhibit reductions in stomatal conductance and, hence, greater internal turgor pressure, which facilitates cell expansion.  In addition, when this phenomenon is coupled with CO2-induced increases in photosynthesis, fruit size will likely increase, thus enhancing yield in this fruit-bearing species.