Plants are a natural source of nitrous oxide even in field conditions as explained by N site preference.

Plants are either recognized to produce nitrous oxide (NO) or considered as a medium to transport soil-produced NO. To date, it is not clear whether in their habitat plants conduit NO produced in soil or are a natural source. We aimed to understand role of plants in NO emissions in field conditions. Therefore, rubber plants (Ficus elastica) were planted in the field; then plant and soil chambers were deployed simultaneously to collect gas samples, and N site preference (SP) of NO was evaluated. The mean SP values of plant and soil emitted NO were -20.85 ± 2.8‰ and -8.85 ± 1.08‰, respectively, and were significantly different (p < 0.0001); while bulk N of plant and soil emitted NO were -10.83 ± 3.33‰ and -22.56 ± 3.37‰, respectively and were similar (p = 0.06). In the current study, soil always acted as a source of NO, while plants were both source and sink. Plant and soil NO fluxes had significant positive exponential relationship with both soil and air temperature. Soil water-filled pore space (WFPS) had significant negative linear relationship with only soil NO fluxes. Plant NO fluxes had significant positive linear relationship with plant respiration rates and negative linear relationship with plant surface areas. Based on the relationship between plant respiration rates and NO fluxes, we suggest that mitochondria are the possible sites of NO formation in plant cells while the relationship between plant surface areas and NO fluxes suggests that roots are the parts of its formation in natural and field conditions. Our results suggest that plants are a natural source of NO even at field conditions and challenge a view that plants are a medium to transport soil-produced NO into the atmosphere.