## 3 Results  
### Light Response Curve Measurements  
This section presents representative results from the light response curve measurements obtained using the developed system (Figure 3). The upward chlorophyll fluorescence (i.e., ChlFUP) exhibited an asymmetric spectral distribution, characterized by lower emission intensity in the red region (<700 nm) and higher intensity in the near-infrared region (>700 nm), primarily due to reabsorption within the leaf tissues (Figure 3a). Although the overall spectral shape of ChlFUP remained largely consistent across varying light intensities, its absolute values varied substantially. Specifically, the red chlorophyll fluorescence emission peak (around 686 nm) increased from 0.04 mW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\) at a light intensity of 30 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\) to about 2.3 mW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\) at 2100 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\), whereas the near-infrared fluorescence peak (around 740 nm) rose from 0.05 mW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\) to 4.2 mW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\) over the same range (Figure 3a). Simultaneously, leaf-reflected radiation (i.e., \(Rad_{\text{UP}}\)) was captured (Figure 3b). Notably, the ratio of \(Rad_{\text{UP}}\) in the red wavelength to that in the blue wavelength varied with light intensity, potentially influenced by chloroplast movement, which may alter light absorption characteristics. The combined measurements of \(Rad_{\text{UP}}\) and \(Rad_{\text{DOWN}}\) provide valuable insights into accurately estimating the fraction of absorbed energy.  
Figure 3: Representative results from light response curve measurements. **(a)** Upward chlorophyll fluorescence (ChIFUP, mW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\)). **(b)** Reflected radiance (\(Rad_{\text{UP}}\), mW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\)). **(c)** Fraction of open PSII reaction centers derived from PAM parameters (\(q_{\text{L,PAM}}\)). **(d)** Non-photochemical quenching derived from PAM parameters (NFQ). **(e)** Net photosynthesis (\(A_{\text{net}}\), \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\)). **(f)** Stomatal conductance (\(g_{\text{sw}}\), mol m\({}^{-2}\) s\({}^{-1}\)). In panels (**c–f**), the red circles and error bars represent the mean values and corresponding standard deviations of 52 species, respectively, while the gray dots indicate the measurements for individual species.  
In addition to passively induced chlorophyll fluorescence, actively induced chlorophyll fluorescence responded as expected to increasing light intensity. For example, as the light intensity increased from 30 to 2100 umol m\({}^{-2}\) s\({}^{-1}\), \(q_{\mathrm{L,PAM}}\) declined progressively from 0.91 to approximately 0.17. In contrast, non-photochemical quenching (NPQ) exhibited an upward trend, rising from 0.92 to a stable value of about 3.12 under high light conditions. The responses of \(A_{\mathrm{net}}\) and stomatal conductance (\(g_{\mathrm{sw}}\)) to light intensity are also presented in Figure 3e,f. Both \(A_{\mathrm{net}}\) and \(g_{\mathrm{sw}}\) increased rapidly at low light levels, eventually reaching saturation at higher intensities. At saturation light intensity, \(A_{\mathrm{net}}\) and \(g_{\mathrm{sw}}\) stabilized at approximately 10 umol m\({}^{-2}\) s\({}^{-1}\) and 0.11 mol m\({}^{-2}\) s\({}^{-1}\), respectively.