Direct canopy uptake of atmospheric reactive N: A significant pathway for airborne nitrogen input to rice paddy ecosystems

Increased atmospheric reactive nitrogen (ARN) has significant impacts on N balance in rice ecosystems. As an important N deposition process, knowledge on direct canopy uptake of rice is limited. A water-culture rice-growing system with 15N labeled nutrient solution was developed to assess canopy uptake of ARN under field conditions. Gross uptake was assessed using plant N partitioning approach and net gain of ARN through canopy uptake was estimated based on N balance in the system. We found gross uptake was 23.1 and 38.2 kg N·ha-1 during transplantation-elongation and elongation-maturity periods, respectively. However, 26.9 kg N·ha-1 of labeled fertilizer N was lost from rice canopy. Therefore, net gain of ARN via canopy exchange was 34.3 kg N·ha-1 over the whole growing season. Our results demonstrate high amount of direct canopy uptake of ARN input to rice ecosystems—an important N process that has not been considered in present N budget establishment.