Effect of Altitude on the Response of Net Photosynthetic Rate to Carbon Dioxide Increase by Spring Wheat

The partial pressure of CO(2) in air decreases with the increase in altitude. Therefore, increase in molar concentration of CO(2) is smaller at higher altitudes than at lower altitudes for increases in molar fraction of CO(2). This study aimed to predict the effect of global CO(2) increase on net photosynthetic rate of spring wheat (Tritium aestivum L.) at high altitudes. The net photosynthetic rate of spring wheat grown in Lhasa (3688 in above sea level), China, was compared with that of the same cultivar grown in Sapporo (15 m above sea level), Japan. At the current level of CO2, it was significantly lower in Lhasa than in Sapporo, and stomatal conductance, chlorophyll content (SPAD value) and apparent quantum yield were similar in both locations. The interaction of CO(2) level and altitude was suggested; the amount of increase in net photosynthetic rate caused by increase in CO(2) was smaller at high altitudes than at low altitudes. Lower CO(2) partial pressure at higher altitude could explain the difference in net photosynthetic rate between altitudes, and the interaction of CO(2) level and altitude