## Results
### Measured CO\({}_{2}\) Fluxes  
#### 3.2.1 Influence of Tillage System  
Influence of measurement date in NEE was significant on both sites, as NEE increased during the active period of growth, and remained close to zero during winter (Figure 3a,b, Tables 1 and 2).  
During spring, the mid-day NEE peaked to \(-204\) kg CO\({}_{2}\)-C ha\({}^{-1}\) day\({}^{-1}\) before losing sink strength due to decreased photosynthesis with increasing levels of plant maturity. Average measured NEE across N treatments (absolute values) were significantly higher under CT system than NT on the upland site, but tillage system did not influence NEE rates on the bottom  
Figure 3: Dynamics of (**a**,**b**) net ecosystem exchange (NEE) of CO\({}_{2}\), (**c**,**d**) gross primary production (GPP), (**e**,**f**) ecosystem respiration (ER), and (**g**,**h**) soil respiration (SR) fluxes from plots managed by no-till and conventional-till. Each point represents average fluxes across all N treatments under a tillage system. Error bars represent the spatial variations at plots (standard error, \(n=12\)). Unidirectional error bars are shown for clarity.  
The dynamics of GPP mostly followed patterns similar to NEE. Mid-day GPP reached \(-\)245 kg CO\({}_{2}\)-C ha\({}^{-1}\) day\({}^{-1}\) in mid-November (Figure 3c,d). Thereafter, GPP rates declined as the plants underwent dormancy during winter. During spring, mid-day GPP peaked at \(-\)267 kg CO\({}_{2}\)-C ha\({}^{-1}\) day\({}^{-1}\) before losing sink strength due to decreased photosynthesis with increasing level of plant maturity. Influence of tillage system was significant on GPP in both sites, with higher GPP rates observed for CT on the upland site and NT on the bottomland site. However, these differences represented differences of only 8%-12% (Tables 1 and 2).  
The dynamics of ER mostly mirrored the dynamics of GPP (Figure 3e,f). Mid-day ER reached 68 kg CO\({}_{2}\)-C ha\({}^{-1}\) day\({}^{-1}\) in November 2016. Thereafter, ER rates declined as the plants underwent dormancy during winter and temperature declined. During spring, the mid-day ER increased to 97 kg CO\({}_{2}\)-C ha\({}^{-1}\) day\({}^{-1}\), then declined due to senescence of plants, despite increased temperatures. The influence of tillage system was significant on ER at both sites, with higher ER rates observed from CT on upland site and from NT on the bottomland site. However, the difference was only \(\sim\)10% on both sites (Tables 1 and 2).  
The dynamics of SR mostly followed temperature, since fluxes remained low in winter and increased in the spring (Figure 3g,h). Unlike ER fluxes, SR rates did not decline during April-May  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Influence** & \multicolumn{2}{c}{**NEE**} & \multicolumn{2}{c}{**GPP**} & \multicolumn{2}{c}{**ER**} & \multicolumn{2}{c}{**SR**} \\ \hline  & **Up** & **Bot** & **Up** & **Bot** & **Up** & **Bot** & **Up** & **Bot** \\ \hline Tillage (T) & **\textless{}0.01** & 0.17 & **\textless{}0.01** & **0.03** & **0.00** & **\textless{}0.01** & 0.16 & **\textless{}0.01** \\ \hline Nitrogen (N) & 0.09 & **0.01** & 0.07 & **\textless{  
2017 since SR did not have plant component. The main effect of tillage on SR was not significant on the upland site, but NT system had significantly higher SR on the bottomland site, albeit the difference was minimal (Tables 1 and 2).