## 3 Results
### Temporal Distributions of Carbon Fluxes for the Selected Major Land Uses
#### 3.4.1 Temporal Distributions of GPP  
Developed land of ET climate zone showed higher monthly GPP as compared to SC climate zone (Figure 10a). Both locations had higher GPP during the summer and lower GPP during the winter. ET climate zone had highest and lowest GPP (404 and 42 g C m\({}^{-2}\) mo\({}^{-1}\)) in July 2015 and December 2018, whereas SC climate zone had the highest and lowest GPP (224 and 33 g C m\({}^{-2}\) mo\({}^{-1}\)) in June 2015 and December 2018. Each summer, except 2018, compared to other seasons, these climate zones received higher precipitation during the study period. However, ET climate zone received more precipitation than the SC climate zone. R\({}^{2}\) and \(p\)-values (0.78 to 0.56 and 0.0195 to 0.0001) for GPP for developed land in ET and SC climate zones showed reasonable correlations each year (Table 4). In comparison, 50% of monthly GPP values were between 100 and 295, and 68 and 167 g C m\({}^{-2}\) mo\({}^{-1}\), respectively, in ET and SC climate zones. Figure 11a shows a larger range of GPP in ET climate zone than SC climate zone. Figure 10: Temporal distributions of monthly precipitation, GPP (**a–e**) and NEE (**f–j**) of five major land-use categories: Cropland (crop), forestland (forest), pastureland (pasture), shrubland (shrub) and developed land (developed) at each selected climate zone in Texas. Note: HP = High Plains; LRP = Low Rolling Plains; ET = East Texas; EP = Edwards Plateau; SC = South Central; TP = Trans Pecos; UC = Upper Coast; NC = North Central; S = Southern; LV = Lower Valley. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Coefficient of Determination (R\({}^{2}\))**} \\ \hline \multirow{2}{*}{**LAND-use**} & \multicolumn{6}{c}{**GPP**} & \multicolumn{6}{c}{**NEE**} \\ \cline{2-9}  & **2015** & **2016** & **2017** & **2018** & **2015** & **2016** & **2017** & **2018** \\ \hline Developed & \multirow{3}{*}{0.56} & 0.70 & 0.78 & 0.63 & 0.50 & 0.62 & 0.77 & 0.57 \\ land & (0.0195) & (0.0006) & (0.0001) & (0.0022) & (0.0322) & (0.0024) & (0.0002) & (0.0045) \\ Forestland & 0.67 & 0.50 & 0.33 & 0.21 & 0.81 & 0.53 & 0.17 & 0.03 \\ (ET, TP) & (0.0068) & (0.0106) & **(0.0501)** & **(0.1392)** & (0.0009) & (0.0071) & **(0.1813)** & **(0.5779)** \\ Shrukl & 0.95 & 0.68 & 0.44 & 0.75 & 0.93 & 0.64 & 0.20 & 0.61 \\ (EP, TP) & (\(<\)0.0001) & (0.0010) & (0.0188) & (0.0003) & (\(<\)0.0001) & (0.0017) & **(0.1435)** & (0.0027) \\ Cropland & 0.79 & 0.69 & 0.61 & 0.53 & 0.59 & 0.45 & 0.40 & 0.27 \\ (HP, UC) & (0.0013) & (0.0008) & (0.0028) & (0.0072) & (0.0155) & (0.0178) & (0.0284) & **(0.0819)** \\ Pastuneland & 0.95 & 0.99 & 0.61 & 0.76 & 0.94 & 0.93 & 0.45 & 0.50 \\ (ET, NC) & (\(<\)0.0001) & (\(<\)0.0001) & (0.0026) & (0.0002) & (\(<\)0.0001) & (\(<\)0.0001) & (0.0170) & (0.0097) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Coefficient of determination (R\({}^{2}\)) and p-value (inside parentheses) for each land-use category at two different climate zones. It shows the correlation between GPP and NEE for the same land-use type at two climate zones. Note: The bold values are greater than the 0.05 significance level. Figure 11: Box and Whisker plots of monthly (**a**) GPP distributions and (**b**) NEE distributions for five major land uses at each selected climate zone in the state of Texas. Note: C = cropland, F = forestland, P = pastureland, S = shrubland, and D = developed land. The white circles represent the mean, the solid horizontal lines represent the median, and gray circles represent outliers. Upper horizontal line = maximum, lower horizontal line= minimum, top of the box = upper quartile, bottom of the box = lower quartile, upper quartile to maximum = upper whisker, and the lower quartile to minimum = lower whisker. Forestland of ET climate zone showed highest (255 g C m\({}^{-2}\) mo\({}^{-1}\)) and lowest (65 g C m\({}^{-2}\) mo\({}^{-1}\)) GPP in June 2015 and December 2018.