## 3 Results
### Growing Season and Annual Carbon Dioxide Balances  
The cumulative NEE fluxes for the respective growing seasons of 2021 and 2022 are shown in Figure 13. These two periods differ from each other. In 2021, cumulative seasonal NEE was positive in all treatments, indicating that the meadow was a net CO\({}_{2}\) emitter. However, in 2022, the opposite pattern was observed--the negative NEE indicates that the meadow was a net sink of CO\({}_{2}\) for all treatments. These differences might be related to warmer and wetter conditions in 2022, when the annual and growing season average air temperatures were higher than in 2021 by 1.0 \({}^{\circ}\)C and 0.6 \({}^{\circ}\)C, respectively, while the annual sum of precipitation was higher by 65.2 mm (Table 1). On the other hand, 2021 had higher average soil moisture than 2022 in both sites with higher (HWL) and lower (LWL) WTD (by 12% and 10%, respectively).  
The highest (most positive) cumulative seasonal NEE in 2021 was reached for LWL_Si (481.77 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\), Table 2). In the case of this plot, the CO\({}_{2}\) emission was higher than for LWL by250.19 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\) (Reco of LWL plot: 231.57 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\)). An inverse relationship was noted for the site with the higher WTD, where the plot with applied AT (HWL_Si) showed a significantly lower cumulative NEE (82.24 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\)) than that for the HWL plot without this treatment (360.31 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\)). Therefore, in the first year of the experiment, the positive effect of the silicon antitranspirant application on the CO\({}_{2}\) balance was confirmed for the site with the higher WTD. Although the HWL_Si plot was also a net source of CO\({}_{2}\) emitted to the atmosphere, the net emission was smaller than for HWL. The same effect was found in the more wet and warmer growing season of 2022, with the difference that cumulative NEE fluxes were negative for all the plots, as indicated above. Nonetheless, the application of an antitranspirant positively affected the CO\({}_{2}\) balance of the meadow, especially at HWL_Si (\(-\)512.18 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\)), where the cumulative seasonal NEE was more than twice as much as for HWL (\(-\)229.55 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\)). The application of antitranspirant also had a positive effect on the CO\({}_{2}\) balance of the site with the lower WTD. Although the differences were much smaller than for the HWL site, the cumulative seasonal NEE was higher (more negative) for LWL_Si (\(-\)166.46 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\)) than for LWL (\(-\)105.69 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).growing season\({}^{-1}\)). To conclude, in the growing season of 2022, the application of the silicon antitranspirant increased net CO\({}_{2}\) assimilation by 123% for the site with a higher WTD and by 58% for the site with a lower WTD.  
Figure 13: Cumulative NEE values for the 2021 and 2022 growing seasons.  
The annual cumulative Reco fluxes were higher in 2021 and ranged from 2291.03 to 2446.85 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).year\({}^{-1}\), whereas in 2022 they ranged from 1847.76 to 2234.95 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).year\({}^{-1}\) (Table 2). The cumulative annual GPP fluxes ranged from \(-1912.36\) to 2397.30 gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).year\({}^{-1}\) in 2021 and from \(-1888.21\) to \(-2565.75\) gCO\({}_{2}\)-C\(\cdot\)m\({}^{-2}\).year\({}^{-1}\) in 2022. Excluding the LWL_Si plot in 2021, in all other treatments in both years, the positive effect of silicon antitranspirant application on CO\({}_{2}\) net balance was confirmed, similarly to the seasonal balances, as indicated above (Table 2).