Do Daily and Seasonal Trends in Leaf Solar Induced Fluorescence Reflect Changes in Photosynthesis, Growth or Light Exposure? [PERSON]  
1 Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong 2522, Australia; [EMAIL_ADDRESS] (Z.M. ); [PERSON]DDRESS] (M.B.A.); [PERSON]ADDRESS] (B.O. ); [PERSON]ADDRESS] (S.A.R.) [PERSON]  
12 Department of Remote Sensing, Global Change Research Institute CAS, Belfida 986/4a, CZ-60300 Brno, Czech Republic  
2  
[PERSON]  
1 Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong 2522, Australia; [EMAIL_ADDRESS] (Z.M. ); [PERSON]DDRESS] (M.B.A.); [PERSON]ADDRESS] (B.O. ); [PERSON]ADDRESS] (S.A.R.) [PERSON]  
1  
[PERSON]  
1 Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong 2522, Australia; [EMAIL_ADDRESS] (Z.M. ); [PERSON]DDRESS] (M.B.A.); [PERSON]ADDRESS] (B.O. ); [PERSON]ADDRESS] (S.A.R.) 2  
Czech Republic  
2  
Footnote 12: email  
+++ ==WARNING: Truncated because of repetitions==
: {}  
++  
for measurements at the large spatial scales required for precision agriculture and plant phenotyping [4]. In recent years, the focus has shifted to the detection of solar induced fluorescence (SIF), which has shown strong potential as a photosynthesis indicator across spatial scales ranging from the leaf and canopy [5; 6; 7; 8] to global scales [9; 10; 11; 12]. Solar induced chlorophyll fluorescence is a broad-band-red and far-red photon emission from excited chlorophyll (Chl) molecules [13]. Changes in the level of SIF vary in proportion to the amount of absorbed photosynthetically active radiation (APAR) utilized by photochemical processes or dissipated via non-photochemical quenching (NPQ) [14]. However, in order to extract biologically relevant information from the SIF signal, information about the relative proportions of APAR used for photochemistry and NPQ must be known [14]. At large spatial scales, measurements of optical vegetation indices have been used to approximate NPQ and photochemistry. For instance, the photochemical reflectance index (PRI), which responds to changes in violaxanthin pigment de-epoxidation status (DEPS) [15], has potential to approximate information about NPQ. When combined with information from greenness optical indices, such as the normalized difference vegetation index (NDVI) [16], photosynthesis and consequently gross primary production (GPP) can be modelled at global scales [10; 14; 17; 18; 19]. However, how these spectral indices are related to photochemistry, NPQ and SIF cannot be examined at large spatial scales because direct measurements of photochemistry and NPQ are unfeasible. Therefore, leaf-level experiments combining spectral and active fluorescence measurements are needed. At the leaf and small plant scale, it is possible to determine the relative proportions of energy utilized by photochemistry (YPSII/\(\phi\)PSII; for the yield of photosystem II), NPQ (YNPQ) and lost due to constitutive processes (YNO) using active fluorescence approaches, e.g., PAM [20]. By combining active fluorescence with sub-nanometre reflected radiance measurements, the relative APAR partitioning can be examined in relation to SIF, PRI and NDVI. Some studies have observed coincident changes in far-red SIF (SIF\({}_{\text{FR}}\)) and \(\phi\)PSII measured by PAM fluorometers [21] and have examined diurnal and seasonal changes in SIF in crop plants [8]. However, these studies focused only on small-scale canopies in comparison with single leaf PAM measurements. The mismatch between leaf and canopy scales, results in poor correlations between leaf PAM measurements and changes in PAR measured at the canopy [8]. Moreover, to the authors' knowledge, no study has derived APAR partitioning from PAM data (i.e., YPSII, YNPQ and YNO).