Figure 4.

Diurnal courses of Φ_CO2, Φ_PSII, F_v′/F_m′, qP, and NPQ of the youngest fully expanded leaf of maize grown under ambient (○) and elevated CO₂ (•) on five dates during 2004 at SoyFACE, Urbana, IL. Each point is the mean (±se) of the replicate plots measured at that time (n = 4). P values indicate statistical significance of CO₂ and CO₂ × time interaction effects.