## 3 Results
### Controlling Factors of \(R_{\rm S}\)
#### 3.2.2 Relationship between \(\rm R_{\rm S}\) to Flux and Biophysical Controls  
Using Spearman correlations, our results identified relationships from biophysical controls with \(\rm R_{\rm S}\) (Table 6); where VPD was negatively correlated (\(p<0.0001\)) in all sites K showed a negative relationship only in the OG site. Meanwhile, ET and GPP were only correlated in the OG and MS sites, and Tair showed a significant positive relationship at MS \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Site**} & \multicolumn{2}{c}{\(\rm R_{\rm S}\)} & \\  & \multicolumn{2}{c}{**(g C m\({}^{-2}\))**} & \\ \hline  & 2015 & 2016 & 2017 & 2019 \\ OG & 785.70 \(\pm\) 21.66 \({}^{\rm A}\) & 1005.89 \(\pm\) 69.09 \({}^{\rm A}\) & 712.87 \(\pm\) 31.41 \({}^{\rm A}\) & 970.76 \(\pm\) 62.65 \({}^{\rm A}\) \\ MS & 618.16 \(\pm\) 40.47 \({}^{\rm B}\) & 753.77 \(\pm\) 58.31 \({}^{\rm B}\) & 665.32 \(\pm\) 26.22 \({}^{\rm A}\) & 837.38 \(\pm\) 80.08 \({}^{\rm A}\) \\ ES & 728.35 \(\pm\) 48.11 \({}^{\rm B}\) & 786.33 \(\pm\) 34.71 \({}^{\rm B}\) & 681.19 \(\pm\) 17.11 \({}^{\rm A}\) & - \\ \hline \hline \end{tabular}  
* OG = old-growth, MS = mid-secondary, ES = early-secondary forests. Early-secondary site was not sampled during 2019.  
\end{table} 
Table 4: Annual C emission from \(\rm R_{\rm S}\) along a forest succession in tropical dry forest in northwestern Mexico. Data are presented as mean \(\pm\) standard error. Capital letters denote significant differences among sites (\(p<0.05\)). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Site**} & \multirow{2}{*}{**Annual**} & \multicolumn{2}{c}{**Dry Season**} & \\  & & **(umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\))** & **Wet Season** \\ \hline OG & 3.22 \(\pm\) 0.16 \({}^{\rm A}\) & 1.40 \(\pm\) 0.08 \({}^{\rm A}\) & 5.20 \(\pm\) 0.25 \({}^{\rm A}\) \\ MS & 2.73 \(\pm\) 0.17 \({}^{\rm A}\) & 1.11 \(\pm\) 0.07 \({}^{\rm B}\) & 4.52 \(\pm\) 0.26 \({}^{\rm A,B}\) \\ ES & 2.68 \(\pm\) 0.17 \({}^{\rm A}\) & 1.36 \(\pm\) 0.08 \({}^{\rm A}\) & 4.56 \(\pm\) 0.32 \({}^{\rm B}\) \\ \hline \hline \end{tabular}  
* OG = old-growth, MS = mid-secondary, ES = early-secondary forests.  
\end{table} 
Table 3: Mean annual and seasonal rates of soil respiration (\(\rm R_{\rm S}\)) along a forest succession from tropical dry forest in northwestern Mexico. Data are presented as mean \(\pm\) standard error. Capital letters denote significant differences among sites (\(p<0.05\)). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Site**} & \multicolumn{2}{c}{**K**} & \multicolumn{2}{c}{**Q***} & \multicolumn{2}{c}{**Tair**} & **VPD** & **ET** & **GPP** & **SWC** & **TS** \\  & **(W m\({}^{-2}\))** & **(W m\({}^{-2}\))** & **(C)** & **(InP)** & **(mm)** & **(umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\))** & **(m\({}^{-2}\))** & **(C)** \\ \hline OG & 673.27 \(\pm\) 15.61 \({}^{\rm A}\) & 456.40 \(\pm\) 11.77 \({}^{\rm A}\) & 30.01 \(\pm\) 0.21 \({}^{\rm B}\) & 26.77 \(\pm\) 0.60 \({}^{\rm B}\) & 4.14 \(\pm\) 0.19 \({}^{\rm A}\) & 13.48 \(\pm\) 0.64 \({}^{\rm A}\) & 0.20 \(\pm\) 0.00 \({}^{\rm B}\) & 25.84 \(\pm\) 0.42 \({}^{\rm B}\) \\ MS & 490.14 \(\pm\) 19.46 \({}^{\rm B}\) & 336.59 \(\pm\) 15.39 \({}^{\rm B}\) & 28.92 \(\pm\) 0.11 \({}^{\rm C}\) & 27.03 \(\pm\) 0.83 \({}^{\rm B}\) & 2.89 \(\pm\) 0.27 \({}^{\rm B}\) & 5.57 \(\pm\) 0.46 \({}^{\rm C}\) & 0.18 \(\pm\) 0.11 \({}^{\rm C}\) & 26.96 \(\pm\) 0.32 \({}^{\rm A}\) \\ ES & 752.86 \(\pm\) 28.68 \({}^{\rm A}\) & 387.16 \(\pm\) 13.65 \({}^{\rm B}\) & 30.65 \(\pm\) 0.27 \({}^{\rm A}\) & 29.92 \(\pm\) 0.74 \({}^{\rm A}\) & 4.55 \(\pm\) 0.30 \({}^{\rm A}\) & 8.85 \(\pm\) 0.69 \({}^{\rm B}\) & 0.37 \(\pm\) 0.00 \({}^{\rm A}\) & 27.57 \(\pm\) 0.42 \({}^{\rm A}\) \\ \hline \hline \end{tabular}  
* OG = old-growth, MS = mid-secondary, ES = early-secondary forests. Early-secondary site was not sampled during 2019.  
\end{table}