To determine the effects of CO
2 under different atmospheric pressures, we assessed the effects of elevated CO
2 on the growth of spring wheat (
Triticum aestivum L.) in a field experiment in Lhasa (3688 m above sea level), the Tibet Plateau, China, and in a growth chamber (GC) experiment in Sapporo (15 m above sea level), Japan. Open-top chambers (OTCs) were installed at Lhasa and spring wheat was grown under CO
2 at a partial pressure of 23.4 Pa (ambient CO
2) and 38.5 Pa (elevated CO
2, equivalent to a 200 µmol mol
-1 increase). In the OTC experiments, CO
2 was elevated with gas-firing equipment and a blower, so that the air temperature inside the OTC for elevated CO
2 was raised 0.8ºC. In the GC experiment in Sapporo, we used three CO
2 partial pressure levels; 24.8, 39.8 and 59.3 Pa and two air temperature regimes, 11/19ºC and 11/21ºC (night/day). In the OTC experiment, dry weight at harvest was lower in the elevated CO
2 than in the ambient CO
2. In the GC experiment, the effect of the elevation of CO
2 from 24.8 to 39.8 Pa on biomass was greater than that from 39.8 to 59.3 Pa. A 2ºC increase in temperature reduced dry weight at all CO
2 levels and offset the positive effect of CO
2 increase from 39.8 to 59.3 Pa. The difference between the results obtained in the experiments in OTC and GC was not clear and might have involved artifacts such as blower and/or ethylene effects.
View full abstract