## 3 Results
### Dependence of Ecosystem CO\({}_{2}\) Flux Components on Soil Temperature and Moisture
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{8}{c}{**GEP = \(\mathbf{a}\times\mathbf{T}^{2}+\mathbf{b}\times\mathbf{T}+\mathbf{c}\)**} \\ \cline{2-10}  & **a** & **SE(a)** & **b** & **SE(b)** & **c** & **SE(b)** & **RMSE** & \(\mathbf{R}^{2}\) & **P** \\ \hline Across treatments & \(-\)0.065 & 0.006 & 2.419 & 0.198 & \(-\)8.190 & 1.478 & 18.61 & 2.943 & 0.386 & \(<\)0.01 \\ Ambient precipitation & \(-\)0.078a & 0.014 & 2.861 a & 0.398 & \(-\)11.555 a & 2.782 & 18.34 & 3.003 & 0.476 & \(<\)0.01 \\ Decreased precipitation & \(-\)0.043 b & 0.010 & 1.684 b & 0.325 & \(-\)3.321 b & 2.571 & 19.58 & 3.152 & 0.250 & \(<\)0.01 \\ Increased precipitation & \(-\)0.088 a & 0.016 & 3.060 a & 0.458 & \(-\)11.862 a & 3.175 & 17.39 & 2.488 & 0.452 & \(<\)0.01 \\ \hline \multicolumn{10}{c}{\(\mathbf{Re}=\mathbf{a}\times\mathbf{c}^{2}\)} \\ \cline{2-10}  & **a** & **S(fa)** & **b** & **SE(b)** & **Q** & **S(fa)** & **RMSE** & \(\mathbf{R}^{2}\) & **P** \\ \hline Across treatments & 2.575 & 0.134 & 0.052 & 0.003 & 1.682 & 0.050 & 1.548 & 0.429 & \(<\)0.01 \\ Ambient precipitation & 2.293 ab & 0.208 & 0.064 a & 0.005 & 1.896 a & 0.095 & 1.516 & 0.517 & \(<\)0.01 \\ Decreased precipitation & 2.401 a & 0.158 & 0.046 b & 0.004 & 1.584 b & 0.063 & 1.048 & 0.566 & \(<\)0.01 \\ Increased precipitation & 2.024 b & 0.194 & 0.073 a & 0.006 & 2.075 a & 0.125 & 1.437 & 0.554 & \(<\)0.01 \\ \hline \multicolumn{10}{c}{\(\mathbf{Re}=\mathbf{a}\times\mathbf{c}^{2}\)} \\ \cline{2-10}  & **a** & **SE(fa)** & **b** & **SE(b)** & **Q** & **S(fa)** & **RMSE** & \(\mathbf{R}^{2}\) & **P** \\ \hline Across treatments & 1.242 & 0.078 & 0.055 & 0.004 & 1.733 & 0.069 & 0.961 & 0.364 & \(<\)0.01 \\ Ambient precipitation & 1.098 a & 0.113 & 0.067 a & 0.006 & 1.954 a & 0.117 & 0.867 & 0.472 & \(<\)0.01 \\ Decreased precipitation & 1.204 a & 0.105 & 0.050 b & 1.069 a & 0.082 & 0.740 & 0.486 & \(<\)0.01 \\ Increased precipitation & 1.017 a & 0.151 & 0.072 a & 0.009 & 2.054 a & 0.185 & 1.100 & 0.330 & \(<\)0.01 \\ \hline \multicolumn{10}{c}{\(\mathbf{NEE}=\mathbf{a}\times\mathbf{T}^{2}+\mathbf{b}\times\mathbf{T}+\mathbf{c}\)**} \\ \cline{2-10}  & **a** & **S(fa)** & **b** & **SE(b)** & **c** & **SE(fa)** & **T\({}_{\mathbf{0}}\)** (C)** & **RMSE** & \(\mathbf{R}^{2}\) & **P** \\ \hline Across treatments & 0.045 & 0.005 & -1.449 & 0.161 & 4.443 & 1.199 & 16.32 & 2.388 & 0.175 & \(<\)0.01 \\ Ambient precipitation & 0.058 a & 0.011 & -1.889 a & 0.309 & 7.725 a & 2.160 & 16.28 & 2.331 & 0.254 & \(<\)0.01 \\ Decreased precipitation &Figure 8: Relationship between precipitation and gross ecosystem productivity (GEP) or ecosystem respiration (Re) during growing season. Values were averaged across each treatment in each year. Blue is decreased precipitation treatment, red is ambient precipitation treatment, green is increased precipitation treatment. Square was measured in 2013, diamond was measured in 2014, circle was measured in 2015. \(p<0.05\) for both relationships. Figure 7: Relationships between ecosystem CO\({}_{2}\) flux and soil temperature or soil moisture across all the treatments during the measuring period (July 2013 to September 2015). GEP, Re, Rs, and NEE are gross ecosystem productivity, ecosystem respiration, soil respiration, and net ecosystem CO\({}_{2}\) exchange, respectively. Ln(Re) or ln(Rs) is the natural log transformed Re or Rs. The unit of CO\({}_{2}\) flux or natural log transformed CO\({}_{2}\) flux is \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\). \(p<0.05\) for all relationships. In this study, NEE accounted for nearly 60% of GEP and was mainly determined by GEP (NEE = \(1.662-0.666\times\) GEP, RMSE = 1.381, R\({}^{2}\) = 0.777, \(p<0.01\)). The effects of the precipitation treatments on dependence of NEE on soil temperature and moisture were similar to the effects on dependence of GEP. The DP decreased the slope for the NEE-temperature response function but increased the slope for the NEE-moisture response function; IP had the opposite effect on these dependencies (Tables 2 and 3).