## Results
### Diurnal Trends in Solar Induced Fluorescence  
Values of \(\mathrm{SIF_{red}}\) and \(\mathrm{SIF_{FR}}\) for both avocado and orange jasmine leaves changed diurnally in response to increasing leaf PAR (Figure 4A,G). However, the relative rates of change in SIF and leaf PAR differed (Figure 4B,H). SIF was found to increase more rapidly than the increasing leaf PAR during first light exposure in the morning. A plateau or a decrease often followed this rapid SIF increase once maximum leaf PAR was reached. Both \(\mathrm{SIF_{red}}\) and \(\mathrm{SIF_{FR}}\) declined rapidly during the afternoon as leaf PAR decreased and thereafter remained low. Both species showed broadly similar diurnal SIF patterns. However, avocado leaves showed more consistent and less erratic diurnal changes in SIF and consistently higher values of both \(\mathrm{SIF_{red}}\) and \(\mathrm{SIF_{FR}}\). Solar induced chlorophyll fluorescence yields changed little during slow diurnal changes in light intensity, with a tendency to be slightly higher in the morning and afternoon (Figure 4C,I). Fast changes in YSIF were commonly observed during  
Figure 3: Scatterplots of leaf measurements of \(\mathrm{SIF_{red}}\) (red) and \(\mathrm{SIF_{FR}}\) (black) against LIFT measured photosynthetic parameters and leaf PAR from leaves of both avocado (**A–E**) and orange jasmine (**F–J**). LIFT and SIF measurements were collected simultaneously from sunrise to sunset with a three-minute time resolution. Plots show data from all time points and measurement days, where each point represents the mean of six leaf replicates collected at the same time on a single measurement day \(\pm\)3 min. The black and red lines show the linear fit for \(\mathrm{SIF_{red}}\) (red) and \(\mathrm{SIF_{FR}}\) (black). fluctuations in leaf PAR. Under these conditions \(\mathrm{SIF_{FR}}\) decreases lagged behind leaf PAR decreases resulting in higher values of \(\mathrm{YSIF_{FR}}\). Conversely, for \(\mathrm{YSIF_{red}}\), changes were quite erratic and associated with large errors. Changes in photosynthetic parameters were broadly consistent in behaviour across both plant species, with the exception of ETR. Electron transport rates for both leaves of avocado and orange jasmine were found to display similar maximum values (~50 \(\mathrm{\SIUnitSymbolMicro m^{-2}\cdot s^{-1}}\)), but differ in behaviour (Figure 4D,J) during measurements at SHF. In avocado leaves, maximum ETR was achieved  
Figure 4: Diurnal changes in PAR, SIF, SIF yields, photosynthetic parameters and spectral indices measured using a LIFT instrument and QE Pro. The Y axis of each panel shows measured parameters as they change over a diurnal cycle. Each data point represents the mean \(\pm\) SE (vertical bars) of six fully expanded avocado leaves from SHF (**A–F**) and orange jasmine leaves from UOW (**G–L**). All measurements were collected with a mean resolution of \(\sim\)3 min \(\pm\) 3 min per sample and have been smoothed using a centred moving average of the two following and previous measurements. Measurements from 20 December and 13 September 2015 have been selected as illustrative examples of commonly observed diurnal changes in measured parameters in the two examined plant species. during moderate light exposure in the morning and afternoon, with ETR decreasing or plateauing during the middle of the day (Figure 4D). Contrastingly, in orange jasmine, maximum ETR was consistently achieved during the middle of the day, with lower values of ETR during the morning and afternoon (Figure 4J). APAR partitioning in both species was strongly linked to leaf PAR (Figure 4E,K). However, the three yield components (YPSII, YNO and YNPQ) were observed to differ over the course of a day between avocado and orange jasmine leaves. In avocado, high morning leaf PAR resulted in a rapid increase in YNPQ to high levels (\(\sim\)0.8); this change coincided with a rapid decrease in YPSII to low levels (0.2 to 0.1) and a decrease in YNO from a steady value of \(\sim\)0.2 to \(\sim\)0.1 (Figure 4E).