## 2 Materials and Methods
### Data Processing and Analysis  
The eddy covariance flux measurements were processed to 30 min time steps during the full 2017 growing season (Figure 1). The flux measurements obtained on days with corresponding MoniPAM and FLoX collections were selected for further use. Ecosystem respiration (Re) was calculated as an exponential function of air temperature using a relationship developed from nighttime net ecosystem production, measured by the flux tower and corresponding temperature observations [56; 57]. The difference between the CO\({}_{2}\) flux and Re provided the GPP (Figure 1, mg/m\({}^{2}\)/s, shown in green on the right axis). This calculation was supported by the tower's micro-meteorology measurements, including PAR (umol/m\({}^{2}\)/s, Figure 1 in gray on the left axis). Incident PAR was used to estimate the photosynthetic light use efficiency (LUE) [58; 59] of the canopy in the tower footprint, which was calculated as:  
\[\text{LUE}=\text{GPP}/\text{PAR}. \tag{1}\]  
Leaf-level light-adapted PAM fluorescence metrics representative of the canopy were derived by calculating the mean of the values from three MoniPAM emitter-detector probes maintained on fully sunlit leaves, using the simultaneously acquired measurements at 10 min intervals. Large outlier values from a single probe (mean \(\pm\) three standard deviations) were removed, resulting in averaged light-adapted observations of incoming PAR; steady state F (F\({}_{\text{s}}\)), measured shortly before a saturating pulse is applied; and maximum F level (F\({}_{\text{m}}\)'), induced by applying a saturating light pulse which temporarily closes all PS II reactions centers. F\({}_{\text{s}}\) and F\({}_{\text{m}}\) (relative units) [18; 21; 24], were used to calculate the electron transport rate (ETR, umol/m\({}^{2}\)/s\({}^{1}\), Figure 2 in red on the left axis scaled by 10), and the effective photochemical quantum yield of PSII (YII, Figure 2 in blue on the right axis), as:  
\[\text{YII}=(\text{F}_{\text{m}}\text{'}-\text{F}_{\text{s}})/\text{F}_{\text {m}}\text{'}. \tag{2}\]  
The FLoX system [55] collects upwelling and down-welling measurements, which were processed to reflectance and solar induced fluorescence (SIF) using two open-source R packages [60; 61]. The outputs of the processing are: incoming radiance to the surface, top of canopy reflected radiance, apparent reflectance, and SIF estimates at spectral wavelengths associated with both atmospheric oxygen absorption features centered at 683 (SIF\({}_{\rm B}\)) and 760 nm (SIF\({}_{\rm A}\)). Canopy reflectance from the FLoX was used to calculate indices indicative of vegetation green biomass, chlorophyll content, and photosynthetic function (i.e., NDVI, Cl\({}_{\rm red}\) and PRI; Figure 3 and Table 2). SIF\({}_{\rm A}\) and SIF\({}_{\rm B}\) were retrieved by applying the spectral fitting method (SFM) [62] at the original acquisition time-steps (i.e., 1 min). Total SIF\({}_{\rm A+B}\) was calculated as the sum of SIF\({}_{\rm A}\) and SIF\({}_{\rm B}\). Each fluorescence estimate was assigned a quality flag, reporting information related to the illumination stability during the measurement cycle and the internal noise of the instrument at the moment of the data acquisition, which were used for filtering the dataset for saturated data points and anomalous readings [48,62]. Additional screening was done to remove sensor artefacts due to low light levels (i.e., in the early morning and late afternoon, SZA > 75\({}^{\circ}\)), so that only data collected between 8:00 and 17:00 local time were used in the analyses. Figure 3: Seasonal variation in midday canopy gross primary production (GPP, A), absorbed photosynthetically active radiation (APAR, B), leaf photochemical efficiency of photosystem two (YII, C) and electron transport rate (ETR, D), vegetation indices (NDVI, Cl\({}_{\rm red}\) and PRI, E–F), solar induced fluorescence (SIF, G), and SIF yield metrics (SIF\({}_{\rm F}\), H). Each value represents an ANOVA GLM mean of four midday observations (e.g., 11:45–13:15 EDT, 30 min. interval).