## 3 Results  
### Seasonal Patterns of SIF  
According to the seasonal patterns shown in Figure 3, the F760 of wheat and maize showed large day-to-day variations, which agreed well with the daily variation of SWR, except plot 2 for maize. This indicated that SWR might be a main driver for the seasonal patterns of F760, which was consistent with the findings in a temperate deciduous forest [9]. We also found that F760 in the late period (particularly after May for wheat and after September for maize) could not reach the same magnitude as the early growth stage, even as the concurrent SWR was at similar or higher levels (Figure 3). This result implied that seasonal patterns of F760 might also be related to plant phenological stages. Based on the observations of wheat in Figure 3 (can also be seen in Figure S1), gradient values of F760 were also observed after 22 April 2017, during which, wheat was suffering from gradient irrigation treatments (Figure 2b). These gradient F760 over the four plots showed similar daily variations but with a decreasing trend in the order plot 1 \(>\) plot 2 \(>\) plot 3 \(>\) plot 4 (Figure 3 and Figure S1), corresponding to the decreasing order of irrigation amounts in the four plots (Figure 2b). The consistent decreasing trend of F760 with gradient irrigation treatments suggested that water stress may yield lower F760 values and thus suggested that soil moisture was another factor affecting the emission of SIF. It was expected that the seasonal patterns of maize F760 in the four plots should show little differences since rain was applied over the maize during its whole growth season. As expected, F760 in plot 1, plot 3, and plot 4 differed slightly between each other (Figure 3). However, maize F760 in plot 2 showed much lower values than that of the other three plots, particularly in the period between 25 August and 17 September 2017. This abnormal phenomenon may be attributed to the unsuitable spectra collection position that led to a close distance between the bare fiber and the top leaves, which thereby lowered the canopy radiance received by the sensor.  
Similar with F760, the seasonal patterns of AF760 and Fy760 also tracked the seasonal pattern of SWR (Figure 4). This means that SWR still played important roles in driving the seasonal patterns of AF760 and Fy760. However, the covariation of SWR with AF760 and Fy760 was not totally consistent: AF760 changed consistently with SWR during the whole periods, while Fy760 showed a similar situation before May for wheat and before middle September for maize, and a reversed situation after that time (Figure 4). This result also drew the conclusion that the role of plant phenological stages was also important for driving the seasonal patterns of AF760 and Fy760, which was similar with that of F760.  
Furthermore, compared with F760, AF760 and Fy760 exhibited smaller daily fluctuations during the field campaigns (Figure 4 and Figure S1). These smaller fluctuations resulted from the partial removal of solar radiance impacts through the method of F760/PAR and F760/L685. In addition, the water-stress-induced difference of wheat Fy760 among the four plots could be distinguished from 22 April (the time that gradient irrigations were applied), which was obviously earlier than that of F760 and AF760 (gradients among the four plots were observed after May) (Figure 4 and Figure S1). On the contrary, relative to F760, rain-fed maize AF760 showed a smaller difference among plot 1, plot 3, and plot 4 and Fy760 in these three plots (Figure 4 and Figure S1). AF760 and Fy760 of maize in plot 2 still remained lower than that of the other three plots (Figure 4 and Figure S1).  
Figure 3: Seasonal patterns of daily F760 from wheat (left of dashed line) and maize (right of dashed line) in the four plots compared with daily solar radiation (SWR). All measurements of wheat were collected from 28 March to 19 May 2017, while the measurements of maize were collected from July 29 to September 29 of 2017.