# Adjustments to SIF Aid the Interpretation of Drought Responses at the Caatinga of Northeast Brazil
## 3 Results
### SIF and Climate: Linear Mixed Model Analysis
\begin{table}
\begin{tabular}{l l c c c c c} \hline \hline
**Model** & **Fixed Effect** & **Estimate** & **SE** & **Chisq** & **df** & **_p_ & \\ \hline \(\text{SIF}_{FR}\) & Temperature (T) & \(-0.306\) & \(0.039\) & \(76.887\) & 1 & \(<\)0.001 & *** \\  & Soil Moisture (SM) & \(0.614\) & \(0.032\) & \(395.087\) & 1 & \(<\)0.001 & *** \\  & T : SM & \(0.035\) & \(0.016\) & \(5.057\) & 1 & 0.025 & * \\  & Ecoreigion & & & \(670.376\) & 8 & \(<\)0.001 & *** \\ \hline \(d\text{SIF}_{FR}\) & Temperature (T) & \(-0.340\) & \(0.040\) & \(90.180\) & 1 & \(<\)0.001 & *** \\  & Soil Moisture (SM) & \(0.571\) & \(0.033\) & \(325.760\) & 1 & \(<\)0.001 & *** \\  & T : SM & \(-0.069\) & \(0.015\) & \(5.070\) & 1 & 0.0243 & * \\  & Ecoreigion & & & \(645.610\) & 8 & \(<\)0.001 & *** \\ \hline \(\text{SIF}_{FR}\)-Prod & Temperature (T) & \(-0.386\) & \(0.034\) & \(110.730\) & 1 & \(<\)0.001 & *** \\  & Soil Moisture (SM) & \(0.556\) & \(0.028\) & \(541.120\) & 1 & \(<\)0.001 & *** \\  & T : SM & \(-0.054\) & \(0.013\) & \(16.290\) & 1 & \(<\)0.001 & *** \\  & Ecoreigion & & & \(1149.750\) & 8 & \(<\)0.001 & *** \\ \hline \(\text{SIF}_{FR}\)-SZA & Temperature (T) & \(-0.165\) & \(0.017\) & \(101.921\) & 1 & \(<\)0.001 & *** \\  & Soil Moisture (SM) & \(0.239\) & \(0.014\) & \(325.115\) & 1 & \(<\)0.001 & *** \\  & T : SM & \(0.005\) & \(0.007\) & \(0.481\) & 1 & 0.488 & \\  & Ecoreigion & & & \(599.259\) & 8 & \(<\)0.001 & *** \\ \hline \(\text{SIF}_{FR}\)-Yield & Temperature (T) & \(-0.071\) & \(0.049\) & \(11.330\) & 1 & 0.148 & \\  & Soil Moisture (SM) & \(0.678\) & \(0.041\) & \(219.486\) & 1 & \(<\)0.001 & *** \\  & T : SM & \(0.150\) & \(0.021\) & \(51.682\) & 1 & \(<\)0.001 & *** \\  & Ecoreigion & & & \(199.573\) & 8 & \(<\)0.001 & *** \\ \hline \(\text{SIF}_{R}\) & Temperature (T) & \(-0.210\) & \(0.057\) & \(21.645\) & 1 & \(<\)0.001 & *** \\  & Soil Moisture (SM) & \(0.542\) & \(0.048\) & \(126.721\) & 1 & \(<\)0.001 & *** \\  & T : SM & \(0.065\) & \(0.024\) & \(7.180\) & 1 & 0.007 & * \\  & Ecoreigion & & & \(344.070\) & 8 & \(<\)0.001 & *** \\ \hline \(\text{SIF}_{R/FR}\) & Temperature (T) & \(0.003\) & \(0.068\) & \(0.000\) & 1 & 0.985 & \\  & Soil Moisture (SM) & \(-0.089\) & \(0.068\) & \(2.088\) & 1 & 0.148 & \\  & T : SM & \(0.004\) & \(0.045\) & \(0.009\) & 1 & 0.925 & \\  & Ecoreigion & & & \(2.467\) & 8 & 0.963 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Linear Mixed Models’ Fixed Effects—“SE” is the Standard Error of each fixed effect estimate, “Chisq” is the chisquare value from each Wald type II test, “df” is the degree of freedom of each effect in its Wald type II test, “_p_” is the probability value of each Wald test. \(\text{SIF}_{FR}\) is Sun-Induced Fluorescence at the far-red peak; \(d\text{SIF}_{FR}\) is the daily average of SIF based on a clear sky PAR proxy; \(\text{SIF}_{FR}\)-Prod is the product of \(\text{SIF}_{FR}\) by NDVI; \(\text{SIF}_{FR}\)-SZA is the quotient of \(\text{SIF}_{FR}\) by the cosine of the Sun’s Zenith Angle (SZA); \(\text{SIF}_{FR}\)-Yield is the quotient of \(\text{SIF}_{FR}\) by NDVI; For all models above: \(n=1179\); \(Month=12\); \(Month\):Year = \(131\). \(\text{SIF}_{R}\) is Sun-Induced Fluorescence at the red peak; \(\text{SIF}_{R/FR}\) is the ratio between \(\text{SIF}_{R}\) and \(\text{SIF}_{FR}\). For the last two models: \(n=747\); _Month:Year = \(83\)_. Significance levels are marked according to the following legend: *** for \(p<0.001\) and * for \(p<0.05\). Since the complete results of all these models would be too extensive to show here (6 models for each of the 9 ecoregions, totaling 54 models). Moreover, since many of the tested response variables show similar results as to what can be observed for the holistic models presented above, we chose to show only the slopes of tested fixed effects in graphical format for the models using \(\text{SIF}_{FR}\) and \(\text{SIF}_{FR}\)-Yield (Figures 6). For \(\text{SIF}_{FR}\) ecoregion-specific LMMs, soil moisture was the most significant fixed effect.