## 3 Results
### GPP, Reco, and NEE Fluxes
#### 3.2.3 Net Ecosystem Exchange (NEE)  
The daily NEE fluxes for individual plots in each year are shown in Figure 10a,b. There were both positive (indicating ecosystem respiration outweighs assimilation rates) and negative daily NEE fluxes in each of the cuts. The exception is the third cut of 2021, when the daily NEE of the HWL_Si, LWL, and LWL_Si plots had only positive values. The highest (most negative) daily NEE fluxes were recorded in the first cut of 2022 and were equal to \(-\)12.01 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) for HWL, \(-\)24.28 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) for HWL_Si, \(-\)10.56 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) for LWL, and \(-\)13.64 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) for LWL_Si. The average daily NEE fluxes for the 2022 growing season amounted to \(-\)0.93 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (HWL), \(-\)2.07 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (HWL, Si), \(-\)0.43 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (LWL), and \(-\)0.67 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (LWL_Si). The 2021 growing season was characterized by higher (positive) average values of NEE, indicating that CO\({}_{2}\) emissions prevailed. The daily average NEE fluxes reached 1.48 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (HWL), 0.34 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (HWL_Si), 0.95 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (LWL), and 1.97 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\) (LWL_Si). Similarly to the analyses above, the Wilcoxon matched-pairs test showed that WTD was a factor differentiating the daily NEE fluxes between plots (Figure 11). In most cuts, daily NEE values differed significantly (\(p<0.05\)) between the plots with higher (HWL) and lower (LWL) water table depth. Only in the second cut of 2022, no significant differences were found between these plots. This is most likely due to the WTD of this period being very low, and hence differences in soil moisture between the two sites were minor and did not exceed 2% (18% at HWL vs. 16% at LWL). Application of the antitranspirant at the site with the higher WTD significantly affected the daily NEE fluxes in each of the analyzed cuts. For the area with the lower WTD, statistically significant differences were observed between LWL and LWL_Si only in the second and third cut in 2021 and the first cut in 2022. Figure 9: Cumulative Reco fluxes for individual plots in each cut in 2021–2022. In the other periods, the daily NEE values of these plots were not significantly different. To conclude, WTD significantly differentiates the daily NEE fluxes, while the application of antitranspirant significantly affects the NEE values only in the site with a higher WTD. The cumulative NEE fluxes in the period of the first cut in both years are negative for all the treatments, indicating that the meadow assimilated more CO2 than it emitted to the atmosphere, and was a net sink of CO2 (Figure 12). In both periods, the largest net assimilation was observed at the HWL_Si, where the cumulative NEE reached up to \(-205.16\) gCO2-C-m-2.cut-1 in 2021 and \(-672.37\) gCO2-C-m-2.cut-1 in 2022. For the second cut of 2021, the HWL_Si plot still acted as the largest sink, with a cumulative NEE reaching \(-278.85\) gCO2-C-m-2.cut-1. However, in this case, positive NEE values were obtained in the plot with a higher WTD without AT application (\(8.20\) gCO2-C-m-2.cut-1) indicating that emissions outweighed CO2 assimilation. Interestingly, the LWL and LWL_Si plots also acted as net sinks of CO2 during the second cut of 2021, with cumulative NEE values of \(-201.99\) gCO2-C-m-2.cut-1 and \(-79.88\) gCO2-C-m-2.cut-1 for LWL and LWL_Si, respectively. The positive effect of AT in the site with a higher WTD was also observed in the second cut of 2022, when the HWL_Si plot was the only one to have a negative cumulative NEE.