## 4 Discussion
We suggest higher resolution SIF\({}_{\text{d}}\) data coupled with vegetation indices, such as the photochemical reflectance index and enhanced vegetation index, measured in conjunction with temperature and precipitation, for instance. Mean EBF SIF\({}_{\text{d}}\) is significantly higher relative to other classes within each biome highlighting the rate of SIF\({}_{\text{d}}\) for EBF is significantly higher in most climatic and geographic regions than its vegetation neighbors (Figure 4). These results are consistent with studies, such as [PERSON] et al. (2018), who examined OCO-2 SIF measurements and GPP from flux towers at 64 sites across the globe and found tropical forests had higher SIF in comparison with other vegetation classes [42]. However, the same study showed SIF\({}_{\text{d}}\) in GRA was lower, while, we show mean SIF\({}_{\text{d}}\) of GRA is not significantly different than other vegetation class mean SIF\({}_{\text{d}}\) in four biomes (Atlantic Forest, Caatinga, Pampa, Pantanal; Figure 4) and total integrated GRA SIF\({}_{\text{d}}\) in the Caatinga exceeds DBF and SAV total integrated SIF\({}_{\text{d}}\). We acknowledge, however, their study did not include data from South America and specifically examined locations with flux towers, making it difficult to compare results directly, highlighting the importance of scale and sampling location on results, and emphasizing the need for more multiscale data and research of a variety of tropical vegetation classes [42]. We examined relationships of SIF\({}_{\text{d}}\) to T\({}_{\text{can}}\), T\({}_{\text{air}}\), and VPD, to identify potential relationships between SIF\({}_{\text{d}}\) and the environment. Temperature is one of the most influential abiotic factors on photosynthesis and GPP, affecting physiological functioning, distribution and range shifts, and competitive success of species e.g., [4; 7; 8; 13; 140; 144; 145; 146; 147; 148]. Most research has focused on T\({}_{\text{air}}\) to examine the relationships between plant function and temperature, but recent studies have shown that T\({}_{\text{air}}\) may not capture thermal properties of vegetation microclimate and environment. T\({}_{\text{can}}\) has been shown to differ from T\({}_{\text{air}}\) in that T\({}_{\text{can}}\) is generally warmer than Tair and more coupled to water and radiative processes [140; 146; 149; 150; 151; 152]. VPD influences stomatal conductance and, as such is a good metric for water stress conditions, thus lower values of VPD are generally associated with more favorable photosynthetic activity conditions for vegetation. Our results show that most biomes are most strongly related to VPD and then T\({}_{\text{can}}\), followed by T\({}_{\text{air}}\). These results support recent studies showing that T\({}_{\text{can}}\) is potentially more related to photosynthetic function in tropical regions than T\({}_{\text{air}}\) and serve to provide incentive to further elucidate SIF\({}_{\text{d}}\) relationships to these variables [85; 153]. We compared total integrated SIF\({}_{\text{d}}\) to the length of season and found that the length of season explains only 30% of the variation in total integrated SIF\({}_{\text{d}}\) (Figure 6; Adjusted R\({}^{2}\) = 0.30, m = 0.01, \(p\) < 0.001); therefore, differential physiological functioning (photosynthetic activity) responses of vegetation classes' SIF to environmental factors are potentially more influential on the seasonal levels of SIF\({}_{\text{d}}\). This result is an important first step to understanding productivity of multiple tropical vegetation classes. Our study quantifies relative SIF among vegetation classes within and across biomes. These results are most certainly also related to structure and incoming and radiation and tightly coupled to the latitude and elevation of each biome.