## 1 Introduction  
Light energy absorbed by plants is primarily dissipated through three pathways: driving electron transport, re-emission as chlorophyll fluorescence in the long-wavelength range (640-850 nm), or dissipation as heat [1, 2]. Chlorophyll fluorescence is highly sensitive to variations in light intensity [3, 4]. The temporal variation in chlorophyll fluorescence induced by actively applying additional light beyond ambient light conditions is referred to as chlorophyll fluorescence kinetics [5, 6]. Numerous studies have leveraged chlorophyll fluorescence kinetics to rapidly assess photosynthetic physiological processes, leading to the development of various active fluorometers, such as pulse amplitude-modulated (PAM) fluorometers [7, 8]. These advances have positioned chlorophyll fluorescence as a pivotal tool in photosynthesis research [9]. Recent advances in retrieving narrowband (e.g., the telluric oxygen absorption at 760 nm) solar-induced chlorophyll fluorescence (SIF) from various platforms (e.g., ground [10], air-borne [11], and satellite [12]) have created significant interest in its potential applications for estimating gross primary productivity (GPP) and analyzing photosynthetic physiological processes [13; 14]. However, most current applications of SIF rely on empirical SIF-GPP relationships, which limits the universality and scalability of GPP estimation using SIF [15]. This limitation arises because the retrieved narrowband SIF provides limited physiological information, as it can only be retrieved under stable light conditions [13; 16]. [PERSON] et al. [17] introduced a mechanistic light reaction (MLR) model linking broadband chlorophyll fluorescence from Photosystem II (PSII) to the actual electron transport rate, drawing on classical chlorophyll fluorescence kinetics and SIF emission theory. Subsequent studies have shown that the MLR model has good potential to accurately estimate the photosynthetic carbon fixation at both the leaf and canopy scales [18; 19; 20]. However, it should be noted that the fraction of open PSII reaction centers (\(q_{\mathrm{L}}\)), a key parameter of the MLR model, is difficult to observe directly at scales beyond the leaf level. Currently, most \(q_{\mathrm{L}}\) estimation methods rely on empirical relationships with PAR, which may fail to account for the influence of other environmental factors (e.g., temperature) and plant physiological dynamics on \(q_{\mathrm{L}}\)[21; 22]. Based on a global sensitivity analysis of a recently developed mechanical model of photosynthesis [23], [PERSON] et al. [22] identified that the broadband chlorophyll fluorescence emitted from PSII (\(\mathrm{ChlF_{PSII}}\)) and leaf temperature (\(T_{\mathrm{Leaf}}\)) are the two major predictors of \(q_{\mathrm{L}}\). Notably, in comparison with \(q_{\mathrm{L}}\) estimations based on PAR, \(q_{\mathrm{L}}\) derived from \(\mathrm{ChlF_{PSII}}\) is better at capturing the diurnal dynamics of GPP [22]. The estimation of \(q_{\mathrm{L}}\) at large scales using \(\mathrm{ChlF_{PSII}}\) requires fitting the parameters of the \(\mathrm{ChlF_{PSII}}\)-\(q_{\mathrm{L}}\) relationship for different species. Therefore, it is essential to develop instruments capable of concurrently measuring actively and passively induced chlorophyll fluorescence, thereby enabling the establishment of the \(\mathrm{ChlF_{PSII}}\)-\(q_{\mathrm{L}}\) relationships across diverse species. To date, many studies have focused on simultaneous observation of actively and passively induced chlorophyll fluorescence in relation to photosynthesis. For example, [PERSON] et al. [24] modified the transparent chamber of a portable gas exchange system by integrating it with a PAM fluorometer and a spectrometer, enabling the simultaneous observation of gas exchange and chlorophyll fluorescence from the adaxial side of the leaf. Similarly, [PERSON] et al.