Fig. 2 CO₂ uptake (PS rate) by a leaf with increasing photon flux density (PFD). Departure from the initial slope (which defines the minimum quantum requirement) occurs as CO₂ becomes limiting and photosynthesis approaches a maximum, light-saturated rate (A_max). The shaded area represents what Björkman and Demmig-Adams (1994) term "excess PFD"

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