(1) maximum ETR (maximal
ETR at saturating irradiance), (2) photosynthetic efficiency
(α, initial slope of P-I curve that indicates the efficiency of
electron transport), (3) light saturation (Ik, light intensity approximating
onset of photosynthetic saturation), and (4)
photoinhibition (β, initial slope of P-I curve at the end of the
saturation phase) by fitting the P-I curves to a hyperbolic
tangent model with photoinhibition, following Platt et al.