## 4 Discussion  
This study assembled a set of complementary observations for corn across the crop growth stages, including canopy GPP and leaf and canopy fluorescence metrics, to investigate their complex dynamic behavior at both diurnal and seasonal scales. During the analysis, we noted minimal effect of clouds and light variability on the FLoX VIs and SIF metrics, which is attributed to the innovative design of the FLoX system, the strategy for automated optimization of the acquisitions, and the data processing routines in which the set of quality flags identified the values acquired during unstable light conditions, generating a set of measurements obtained under a consistent sensor optimization, tailored for the incident light levels. To our knowledge, very few studies have evaluated the correlation between the diurnal (i.e., 8:45-16:15 timeframe) dynamics in photosynthetic function in \(\text{SIF}_{\text{A}}\) and \(\text{SIF}_{\text{B}}\) across seasonality or multiple crop growth stages [42; 49; 50; 51; 52; 66]. Most investigations have focused on the relationship of \(\text{SIF}_{\text{A}}\) to GPP, since \(\text{SIF}_{\text{A}}\) can be obtained globally from satellites, and evaluated either the SIF diurnal patterns or phenological changes. Comparing diurnals, prior research have demonstrated that LUE and \(\text{SIF}_{\text{Ay}}\) co-vary, and that their ratio tends to be constant under high light [27; 50; 51; 66]. This study established stronger correlations of LUE to \(\text{SIF}_{\text{A+By}}\) and to \(\text{SIF}_{\text{By}}\) under high PAR, and less so to \(\text{SIF}_{\text{Ay}}\) (Table 4). Recent studies [45; 51] similarly report significant linear correlations between midday leaf-level chlorophyll fluorescence parameters (i.e., F\({}_{\text{S}}\)), canopy PRI, and chlorophyll VIs for C3 coniferous and deciduous forests. These studies have reported a strong association of \(\text{SIF}_{\text{A}}\) with NDVI and chlorophyll content, which our findings corroborate for a C4 crop, and, in addition, demonstrate that \(\text{SIF}_{\text{B}}\) and \(\text{SIF}_{\text{A+B}}\) were also strongly correlated with NDVI and \(\text{Cl}_{\text{red}}\). Recently, similar diurnal patterns and positive linear relationships between GPP and \(\text{SIF}_{\text{A}}\) were reported using field and satellite observations for C3 and C4 canopies [36; 37; 42; 43; 44; 45; 50]. Based on the established correlations between diurnal observations (i.e., 8:45-16:45), we also report strong positive correlations to GPP for \(\text{SIF}_{\text{A}}\) and \(\text{SIF}_{\text{B}}\). Our results for \(\text{SIF}_{\text{A}}\) concur with the results from these investigations, and show that the relationships between diurnal GPP and \(\text{SIF}_{\text{A}}\) varied with PAR condition (i.e., high vs. low) and growth stage for C4 canopy. Our results report linear relationships between the SIF metrics (i.e., \(\text{SIF}_{\text{A}}\), \(\text{SIF}_{\text{B}}\), and \(\text{SIF}_{\text{A+B}}\)) and YII, and between SIF and ETR, primarily during the mature stage (Figure 6), when canopy chlorophyll levels and \(\text{Cl}_{\text{red}}\) were highest. Prior investigations [42; 44] have reported that YII correlates well with \(\text{SIF}_{\text{Ay}}\) for C3 canopies, which our findings did not support for corn, a C4 crop. Using the complete diurnal sets of observations (i.e., 8:45-16:15), no strong linear relationships were established between the SIF yield metrics (i.e., \(\text{SIF}_{\text{Ay}}\), \(\text{SIF}_{\text{By}}\), \(\text{SIF}_{\text{A+By}}\)) and either GPP or LUE, which could be indicative of the complex and nonlinear behavior of their association across the diurnal profile. Deriving consistent diurnal and seasonal estimates of canopy SIF yield remains challenging, due to the difficulties in estimation of the absorbed energy [31; 59].