Quantifying light response of photosynthesis: Addressing the long-standing limitations of non-rectangular hyperbolic model

Abstract

Light intensity (I) fluctuates rapidly and is the most important environmental factor affecting photosynthesis. Accurate characterization of light-response curve of leaf-scale photosynthesis (PN–I curve) is fundamental for understanding PN–I relations at the whole-plant and ecosystem scales. A robust PN–I model should be accurate in reproducing PN–I curves over light-limited, light-saturated, and photoinhibitory I levels, and ideally returning key quantitative traits defining the curves, including initial slope of increase (α), dark respiration rate (RD), the maximum net photosynthetic rate (PNmax), and the corresponding saturation intensity (Isat). We need to improve a model reproduction of (1) PN–I responses over low I levels and (2) the widely reported decline of PN at photoinhibitory I levels. Our observation– modelling comparison, shown by the widely used non-rectangular hyperbolic model, led to (1) underestimation of RD, (2) overestimation of PNmax, and (3) failure in reproducing the photoinhibitory response when I surpassed the cultivar-specific Isat. In contrast, our model addressed the above limitations extremely well. The results highlighted the accuracy and robustness of our model, especially in (1) returning key traits defining the curve and (2) reproducing the curve over both low [i.e., 0–50 μmol(photon) m–2 s–1] and photoinhibitory I levels (i.e., beyond Isat).