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

抄録

The partial pressure of CO₂ in air decreases with the increase in altitude. Therefore, increase in molar concentration of CO₂ is smaller at higher altitudes than at lower altitudes for increases in molar fraction of CO₂. This study aimed to predict the effect of global CO₂ increase on net photosynthetic rate of spring wheat (Triticum aestivum L.) at high altitudes. The net photosynthetic rate of spring wheat grown in Lhasa (3688 m 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 CO₂ level and altitude was suggested; the amount of increase in net photosynthetic rate caused by increase in CO₂ was smaller at high altitudes than at low altitudes. Lower CO₂ partial pressure at higher altitude could explain the difference in net photosynthetic rate between altitudes, and the interaction of CO₂ level and altitude.