## Appendix B Analysis with [PERSON] (2002) and PROSAIL Models  
We used the model of [PERSON] [50] to predict gross primary production (GPP) in Figure 3b. This model integrates a non-rectangular hyperbola leaf light response curve through the canopy, accounting for leaf acclimation to sun and shade conditions. It models GPP from incident photosynthetically active radiation (PAR), the leaf light response parameters of light saturated photosynthetic rate sunlit leaves (A\({}_{\text{leaf}}\)), maximum quantum yield, and a light response curvature parameter. Canopy inputs are leaf area index (LAI), light extinction coefficient, and leaf transmission coefficient. For Figure 3b, we set the quantum yield to 9.118121 \(\times\) 10\({}^{-9}\) Kg CO\({}_{2}\) J\({}^{-1}\) (the average value for C\({}_{3}\) species from [69]), a curvature parameter of 0.9 [50], a proportion of direct radiation of 0.9, an extinction coefficient of 0.5 (spherical leaf angle distributions, [76]), leaf transmission coefficient of 0.1 (see Appendix A, [50]), and a PAR of 435 W PAR m\({}^{-2}\) (equivalent to about 2000 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\)). We varied LAI from 0-5 m\({}^{2}\) m\({}^{-2}\) and A\({}_{\text{leaf}}\) 5-20 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\), approximating the range of community weighted means found at our sites (5.8-19.4 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\)).  
The PROSAIL model predictions in Figure 6 were calculated with the following inputs: 1.5 for leaf structure parameter (typical value for healthy leaves, [73]), 0 for leaf carotenoid and brown pigment content per area (see Appendix A), the average leaf water observed at the field sites (0.0384 g cm\({}^{-2}\)), a spherical leaf angle distribution, hot spot value of 0.01, 10% fraction of diffuse to direct radiation, and a fixed soil reflectance; 0\({}^{\circ}\) for view angle (from nadir), 0\({}^{\circ}\) view-sun angle azimuth difference, and sun zenith angle of 22\({}^{\circ}\) (average value at midday during spring at our sites). LAI was varied from 0 to 5 m\({}^{2}\) m\({}^{-2}\), and leaf chlorophyll content (C\({}_{\text{ab}}\)) or leaf mass per area (LMA) were varied or fixed as specified in the figure panel (Figure 6); fixed values were 30 \(\mu\)g cm\({}^{-2}\) for C\({}_{\text{ab}}\) (see Supplementary Material 5)and 0.024 g cm\({}^{-2}\) for LMA (the average at our sites). The levels of C\({}_{\text{ab}}\) or LMA used in Figure 6 correspond to the leaf photosynthetic rates shown in Figure 3(b) (see Figure 6 legend), and approximate the ranges at the field sites (Figure 4, Supplementary Material 5). The quantitative crosswalk between LMA in Figure 6 and leaf photosynthetic rate (Figure 5 legend) was based on Figure 4. The crosswalk between C\({}_{\text{ab}}\) and leaf photosynthetic rate (Figure 6 legend) was based on [21], which related C\({}_{\text{ab}}\) to the leaf maximum carboxylation and electron transport capacities, and then extrapolated to A\({}_{\text{leaf}}\) following [77] implemented in plantecophys R package [78]. The leaf photosynthesis model assumed a leaf temperature of 25 \({}^{\circ}\)C and an intercellular CO\({}_{2}\) concentration of 256 umol mol\({}^{-1}\) (the average values in our field measurements).