The CO2 Compensation Point of C3 Plants —A Re-Examination II. Intraspecific Variability

Abstract

A wide intraspecific variability of the CO2 compensation concentration (Γ) is reported in the literature. In order to examine this more closely, the influences of light intensity, leaf temperature, leaf age and the after-effects of temperature stress on Γ, net photosynthesis, and CO2 evolution into CO2-free air in light were investigated in different types of plants. Leaf temperature was the only factor investigated which influenced Γ continuously, a similar exponential temperature increase of Γ being found in different plants, except at temperatures above 35°C. Under the influence of all other factors Γ was not changed when net photosynthetic activity was not restricted more than about 50% of the full capacity. With lower net photosynthetic rates, F and respiration in light (expressed as percentage of photosynthesis) increased with decreasing relative rates of net photosynthesis in a hyperbolic relation. However, a high linear correlation (r = 0.96) was found between all absolute values of CO2 evolution into CO2-free air in light and the corresponding absolute values of net photosynthesis, independent of the plant investigated and the factor influencing photosynthesis. This simple relation may be used in order to estimate CO2 losses by respiration in light, measuring solely the net photosynthetic rates.