Figure 1.

Rates of net photosynthesis Pn (blue dots) in sunflower leaves exposed to pulsed lights of frequencies ranging from 125 to 0.1 Hz. The duty ratio was 25% and the averaged light intensity was 575 μmoles photons m⁻² s⁻¹. The black dots represent the rates of dark respiration Rd (-Pn_dark) measured between the 8–10 min periods of pulsed lights of different frequencies. The data presented are the means of four independent measurements and the errors bars are the S.E.M. Note the logarithmic scale for the x-axis.