## 5 Conclusions  
The cumulative uptake of CO\({}_{2}\) from the atmosphere by the transplanted rice was \(25\%\) lower than wheat as the RE/GPP in wheat was much lower than that in rice. Increased respiratory losses were noted as compared to wheat due to the warmer and wetter conditions during the rice growing season. The RE in rice was significantly affected by the soil temperature, whereas the air temperature significantly affected the respiratory losses in wheat. Fluctuations in \(\alpha\) and Pmax were the most important drivers of CO\({}_{2}\) uptake at the different growth stages in both rice and wheat. The highest CO\({}_{2}\) uptake levels were observed at the heading stage in both the crops. Seasonal changes in PAR explained \(69\%\) and \(81\%\) of the variability in the daytime NEE in rice and wheat, respectively. The seasonal NEE fluxes were strongly determined by the development of the crop canopy and CO\({}_{2}\) uptake became dominant during the late vegetative to reproductive stages, turning the wheat and rice field into a carbon sink up until the ripening stage. The fields acted as a CO\({}_{2}\) source around the late maturity and harvesting stage of rice and wheat, when the daily \begin{table}
\begin{tabular}{l l l c c c c c} \hline \hline \multicolumn{2}{c}{**Location**} & **Climate** & **NEE** & **GPP** & **RE** & **RE/GPP** & **Reference** \\ \hline \multirow{6}{*}{Rice} & International Rice Research Institute, Philippines & Tropical & \(-258\) & \(-778\) & \(521\) & \(0.67\) & [34] \\ \cline{2-8}  & Mase paddy site, Japan & Tropical & \(-396\) & \(-1140\) & \(743\) & \(0.65\) & [24] \\ \cline{2-8}  & Central Rice Research Institute, Cuttak, India & Sub-topical monsoon & \(-448\) & \(-811\) & \(363\) & \(0.44\) & [19] \\ \cline{2-8}  & North China Plain, China & Subtropical semi-humid & \(-583\) & \(-1220\) & \(637\) & \(0.52\) & \\  & monsoon & \(-512\) & \(-1135\) & \(623\) & \(0.54\) & [12] \\ \cline{2-8}  & Indian Agricultural Research Institute, New Delhi, India & Sub-topical, semi-arid & \(-368\) & \(-753\) & \(387\) & \(0.51\) & Present study \\ \hline \multirow{6}{*}{Wheat} & Selhausen test site, Germany (First Year) & Temperate & \(-627\) & \(-1304\) & \(676\) & \(0.51\) & [43] \\ \cline{2-8}  & Selhausen test site, Germany (Second Year) & Temperate & \(-537\) & \(-1067\) & \(529\) & \(0.49\) & [43] \\ \cline{1-1} \cline{2-8}  & North China Plain, China & Subtropical semi-humid & \(-438\) & \(-987\) & \(552\) & \(0.56\) & \\ \cline{1-1}  & monsoon climate & \(-431\) & \(-966\) & \(538\) & \(0.56\) & [12] \\ \cline{1-1} \cline{2-8}  & Indian Agricultural Research Institute, New Delhi, India & Subtropical semi-arid & \(-576\) & \(-888\) & \(304\) & \(0.34\) & Present study \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Net ecosystem exchange (NEE), ecosystem respiration (RE) and gross primary productivity (GPP) at different rice and wheat sites. NEE turned positive due to declining photosynthetic activity and enhanced ecosystem respiration from the soil. Intercrop variability in NEE and GPP values were mainly controlled by PAR and AT. The GPP was observed to be positively correlated with RE in both rice and wheat. Rice contributed 39%, 55.9% and 46.2% to the annual totals of NEE, RE and GPP, respectively, while spring wheat contributed 61%, 44.1% and 53.8%. The integrated cumulative NEE, RE and GPP for the annual rice-spring wheat rotation including the fallow period were \(-\)894.16, 832.39 and 1724.55 g C m\({}^{-2}\), respectively. The annual GPP/RE ratio for the rice-spring wheat sequence was observed to be 0.48. The RE/GPP ratio of spring wheat was lower as compared to earlier studies in winter wheat due to its shorter crop duration and irrigated conditions, which ensured the availability of soil moisture. The present results are most valuable in the context of the global carbon budget estimation, which, so far, have mostly been extrapolated from closed-chamber measurements in this major rice-wheat growing region.