## 3 Results and Discussion
### Interannual Variability in CO\({}_{2}\) Fluxes and ET during Dormant Seasons
Monthly NEE values were relatively larger (release of CO\({}_{2}\)) in November (before full senescence of canopy) and March (once roots became more active for the initiation of new aboveground growth). The results indicated that each month during the dormant period was near neutral to a weak source of CO\({}_{2}\), consistent with the findings of a previous study [51] from a prairie pasture in Shidler, OK, USA, showing the pasture to be a small source of CO\({}_{2}\) (\(\sim\)0.71 g C m\({}^{-2}\) d\({}^{-1}\)) for the period of mid-November to mid-March. The monthly average GPP ranged between 24 \(\pm\) 6 and 29 \(\pm\) 4 g C m\({}^{-2}\) for the months between November and March, indicating similar photosynthetic activities during all months of the dormant season. For the November-February period, cumulative ET ranged from 49 \(\pm\) 0.34 mm (2020-2021) to 65 \(\pm\) 0.73 mm (2018-2019) and cumulative NEE ranged from 41 \(\pm\) 1.4 g C m\({}^{-2}\) (2018-2019) to 64 \(\pm\) 2.08 g C m\({}^{-2}\) (2019-2020). Similarly, cumulative GPP ranged from 96 g C m\({}^{-2}\) (2020-2021) to 122 g C m\({}^{-2}\) (2017-2018). Slightly smaller cumulative ET and GPP values during the 2020-2021 non-growing season could be attributed to drier and unusually cooler conditions in February 2021. Figure 6: Daily patterns of evapotranspiration (ET) (**a**), net ecosystem CO\({}_{2}\) exchange (NEE) (**b**), and gross primary production (GPP) (**c**) during non-growing seasons (November–March) in pasture 18. Multi-year (2017/18-2020/21) averages of cumulative ET, NEE, and GPP in P18 for the November-February period were 56 \(\pm\) 7 mm, 52 \(\pm\) 11 g C m\({}^{-2}\), and 107 \(\pm\) 11 g C m\({}^{-2}\), respectively. During the entire dormant season (November-March), cumulative ET was 81 \(\pm\) 0.84 mm in 2017-2018 and 112 \(\pm\) 1.1 mm in 2018-2019, with large differences in ET occurring after mid-March, with cumulative ET of 19 \(\pm\) 0.42 and 38 \(\pm\) 0.7 mm for DOY 74-90 in 2018 and 2019, respectively. However, cumulative GPP for the same period of both years was similar (\(\sim\)12 g C m\({}^{-2}\)). Consequently, cumulative CO\({}_{2}\) fluxes for the November-March period were similar. Cumulative NEE was 62 \(\pm\) 2.13 and 57 \(\pm\) 1.72 g C m\({}^{-2}\) and cumulative GPP was 153 and 125 g C m\({}^{-2}\) in 2017-2018 and 2018-2019, respectively. These results illustrated different impacts of rainfall on CO\({}_{2}\) fluxes and ET during the dormant season by altering the proportions of stomatal and non-stomatal fluxes, mainly in March with rising temperatures. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & ET & NEE & GPP \\ \hline \multicolumn{4}{c}{November} \\ \hline  
2021 & & & \\ Average & 39 & 17 & 27 \\ SD & 13 & 3 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Monthly evapotranspiration (ET, mm), net ecosystem CO\({}_{2}\) exchange (NEE, g C m\({}^{-2}\)), and gross primary production (GPP, g C m\({}^{-2}\)) from November through March in P18. Uncertainty estimates (due to gap filling) of cumulative ET and NEE (\(\pm\) SD, standard deviation) were derived from the SD of data points used to fill gaps. When fluxes in P15 were compared for 2 years, cumulative fluxes for the November-February period were comparable in 2019-2020 and 2020-2021 (63 \(\pm\) 1.05 and 85 \(\pm\) 1.3 mm of ET, 109 \(\pm\) 3.31 and 109 \(\pm\) 3.1 g C m\({}^{-2}\) of NEE, and 94 and 109 g C m\({}^{-2}\) of GPP, respectively). In comparison, cumulative ET, NEE, and GPP for the entire dormant season (November-March) were 104 \(\pm\) 1.3 and 117 \(\pm\) 1.5 mm, 148 \(\pm\) 3.73 and 136 \(\pm\) 3.7 g C m\({}^{-2}\), and 129 and 181 g C m\({}^{-2}\), respectively, during 2019-2020 and 2020-2021. A larger difference for GPP was noted in March 2021 (72 g C m\({}^{-2}\)) than in March 2020 (35 g C m\({}^{-2}\)) due to greater rates of GPP after mid-March 2021 (cumulative GPP of \(\sim\)22 vs. 46 g C m\({}^{-2}\) for DOY 74-90 in 2020 and 2021, respectively).