Fig. 6.
Net CO2 assimilation rate (A) of wheat leaves as a function of the variable IincΦ2/4 (where Iinc is the incident irradiance and Φ2 is the quantum efficiency of PSII electron transport) at ambient air CO2 with 21% (a) and 2% (b) O2 levels. Each data point represents the mean of measurements from four replicated plants. Solid and dotted lines represent regressions for data within the linear range from irradiance levels higher than the break point for increasing (filled circles) and decreasing (open circles) light series, respectively. The dotted regression line is invisible in (b) because it virtually overlaps with the solid line. The extrapolation of these regression lines to the zero IincΦ2/4 level gives an estimation of -Rd, where Rd is the estimated leaf respiration rate in the light (new CF method). The regression lines below the break point are not shown.