Fig. 2.

Experimental protocol. Light treatments were obtained by placing light transmission filters on the top window of the leaf chamber. Environmental parameters of each condition are specified. PAR, photosynthetically active radiation; YPF, yield photosynthetic efficiency; ϕ_c, phytochrome photoequilibrium; ζ, zeta red:far red ratio; VPD leaf, vapour pressure deficit; the UVA-blue domain was defined between 400 nm and 500 nm. (A) Experiment 1. Gas exchange responses to the light treatment. Leaves were first placed in the gas exchange chamber under the white light of the walk-in growth chamber. Each leaf was submitted to the sequence of three light treatments: white light (ambient), neutral shade, and blueless PAR. Results were obtained from a set of young plants (n=5) and then from more developed plants (n=5). (B) Experiment 2. Interaction between blueless PAR and intercellular CO₂ concentrations. Leaves were put into the gas exchange chamber straight under the neutral filter. The blueless PAR filter was then placed on the gas exchange chamber for 60 min. In order to modify the Ci, two levels of CO₂ air concentration were imposed (either 500 or 300 μmol CO₂ mol⁻¹) 20 min after the beginning of the low-blue light treatment. Except for the CO₂, all of the other environmental conditions were maintained as described in Fig. 2A. Two plants were either submitted to an increase or a decrease of the CO₂ air concentration.