###### Abstract
The dual role of ChIF, tracking both PAR absorption (related to plant greenness) but also photoprotection and photosynthesis dynamics, makes ChIF a valuable tool in non-invasive plant stress detection [38; 39] and has been shown to track canopy Gross Primary Production (GPP) [27; 40]. Since the SIF signal is relatively weak compared to canopy reflected radiation, its retrieval is accomplished within Fraunhofer or Telluric absorption bands, such as the oxygen O2B and O2A-bands, located near the fluorescence peaks at circa 687 nm and 760 nm, respectively, using the Fraunhofer Line Discriminator (FLD) principle and its more advanced variants [41]. Furthermore, since the SIF-signal is only emitted by chlorophyll molecules, the signal is potentially less susceptible to non-photosynthetic background, than e.g., soil reflectance-based vegetation indices [42]. In terms of plant nutrient research, the capacity of SIF to detect foliar nutrient contents remains unclear and, to the best of our knowledge, has been limited to studies focusing on N. As such, SIF has been successfully used to estimate foliar N contents in winter wheat (_Trticulum aestivum_) at the leaf and canopy scales [43; 44], as well as in almond (_Prunus dulcis_) on the canopy scale [25]. However, the potential of SIF to detect a wider range of plant nutrients remains to be elucidated. The PRI and CCI indices are optical proxies of plant carotenoid pigment contents, which are closely related to photosynthetic light use efficiency and plant photoprotection. Originally, PRI was found to correlate with the epoxidation state of the xanthophyll cycle pigments as well as photosynthetic efficiency in plants, and CCI was developed as an adaptation of PRI to measure evergreen photosynthesis at various scales [31]. PRI has been found to correlate with leaf level N dynamics in sunflower plants (_Heliantthus annuus_) [45] and conifer seedlings [46], as well as canopy level N dynamics in several annual and perennial species [47; 48]. With these photoprotection indices, N dynamics are expectedly mediated through indirect means, since N deficient plants that would suffer from lower photosynthetic rates would tend to have increased photoprotection [47], which would then be reflected by PRI and CCI. Research by [PERSON] et al. [49] also showed that canopy level PRI was correlated with P contents in several pasture species. Yet, despite the intrinsic potential,the capacity of photoproduction-related indices such as PRI and CCI to investigate a wider range of foliar nutrients is yet to be explored, as are the factors underlying the relationship at the leaf and canopy scales. The goal of this paper is to characterize the relationship between greenness and photoproduction-based vegetation indices, SIF, and the dynamics of foliar macro- and micronutrients in potato plants using both leaf- and canopy-scale observations. We hypothesize that SIF and photoproduction-related indices such as PRI and CCI will be more strongly correlated with foliar micro and macronutrient dynamics compared to vegetation indices such as the NDVI, MTCI, or red-edge, given their more direct coupling to nutrient-related physiological and PAR absorption dynamics. We test this hypothesis by combining observations across fertilization and water stress experiments in order to generate variability in terms of foliar nutrient contents, canopy development, and physiological stress. Finally, using UAV-based measurements, we investigate how the correlations between foliar nutrient contents and leaf spectral indices scale from the leaf to the canopy level, identifying the indices with stronger potential for remote sensing applications.