## 3 Results
### Co\({}_{2}\) Flux Dynamics  
The half-hourly NEE values for each month throughout the study period and their average monthly cycle are shown in Figure 3. The largest hourly variabilities in the NEE occurred in the spring and summer. The peak of the NEE absorbed in the daytime was approximately \(-44\) umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\), occurring in February. In the monthly mean cycle, February showed the highest mean values of the diurnal absorption peak (approximately \(-21.6\) umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)) and the highest mean values of the nocturnal emission (approximately \(10\) umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)). June showed the lowest monthly mean values of peak diurnal absorption (approximately \(-7.0\) umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)) and the lowest monthly mean values of nocturnal emission (approximately \(4.0\) umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)), which are similar to the July diurnal mean. In the monthly averages, GPP and Reco showed strong seasonal variability. The monthly mean values of GPP and Reco were around 3.6 and 2.5 times higher in the summer (January: GPP = 420 g C m\({}^{-2}\) month\({}^{-1}\) and Reco = 376 g C m\({}^{-2}\) month\({}^{-1}\)) than in winter (July: GPP = 117 g C m\({}^{-2}\) month\({}^{-1}\) and Reco = 149 g C m\({}^{-2}\) month\({}^{-1}\)), respectively (Figure 4). The most significant variabilities among the values for a given month occurred in the summer; for instance, in January, the GPP ranged from 312 g C m\({}^{-2}\) month\({}^{-1}\) in 2021 to 487 g C m\({}^{-2}\) month\({}^{-1}\) in 2018, and Reco ranged from 256 g C m\({}^{-2}\) month\({}^{-1}\) in 2021 to 460 g C m\({}^{-2}\) month\({}^{-1}\) in 2018. The lowest variabilities occurred in the cooler months, for example, in June, with GPP between 94 g C m\({}^{-2}\) month\({}^{-1}\) in 2018 and 141 g C m\({}^{-2}\) month\({}^{-1}\) in 2015 and Reco between 115 g C m\({}^{-2}\) month\({}^{-1}\) in 2018 and 144 g C m\({}^{-2}\) month\({}^{-1}\) in 2015 and 2017. In general, in the spring and summer, the GPP was greater than the Reco, \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Periods**} & **No.** & **R\({}_{\text{g}}\)** & **T\({}_{\text{a}}\)** & **Prec** & **NEE** & **GPP** & **Reco** \\  & **of Days** & **(W m\({}^{-2}\))** & **(\({}^{\circ}\)C)** & **[No. of Frost]** & **(mm)** & **(g C m\({}^{-2}\))** & **(g C m\({}^{-2}\))** & **(g C m\({}^{-2}\))** \\ \hline \multicolumn{8}{c}{Warm season} \\ \hline  
\hline \hline \end{tabular}  
NA—not available.  
\end{table} 
Table 2: Periods, number of days, incoming solar radiation (R\({}_{\text{g}}\)), air temperature (T\({}_{\text{a}}\)), precipitation (Prec), net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco) of a subtropical natural pasture of the Pampa biome grazed by cattle. The averages of R\({}_{\text{g}}\), T\({}_{\text{a}}\), and the accumulated Prec, NEE, GPP, and Reco were performed annually in the warm and cold seasons (according to the evaluation periods of cattle grazing in the area). EC uncertainty is included in the annual NEE. resulting in a Reco/GPP ratio = 0.88; between autumn and winter, Reco was greater than the GPP, resulting in Reco/GPP = 1.03. The annual average of Reco/GPP was 0.93, showing that 93% of what was absorbed via photosynthesis was emitted in the form of ecosystem respiration. In absolute values, the largest differences between the GPP and Reco occurred in the spring and summer months. The seasonality of GPP and Reco resulted, on average and throughout the seven years analyzed, in CO\({}_{2}\) absorption for seven months (September to March), represented by negative NEE. In contrast, the system was a CO\({}_{2}\) emitter in the remaining five months (April to August), as represented by positive NEE. However, April and August were, on average, nearly neutral, with greater variability in April (70 g C m\({}^{-2}\) month\({}^{-1}\) in 2018 and \(-20\) g C m\({}^{-2}\) month\({}^{-1}\) in 2021) (Figure 4).