Plants are a natural source of nitrous oxide even in field conditions as explained by 15N site preference

Abstract

Plants are either recognized to produce nitrous oxide (N₂O) or considered as a medium to transport soil-produced N₂O. To date, it is not clear whether in their habitat plants conduit N₂O produced in soil or are a natural source. We aimed to understand role of plants in N₂O 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 ¹⁵N site preference (SP) of N₂O was evaluated. The mean SP values of plant and soil emitted N₂O were -20.85 ± 2.8‰ and -8.85 ± 1.08‰, respectively, and were significantly different (p < 0.0001); while bulk ¹⁵N of plant and soil emitted N₂O 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 N₂O, while plants were both source and sink. Plant and soil N₂O 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 N₂O fluxes. Plant N₂O 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 N₂O fluxes, we suggest that mitochondria are the possible sites of N₂O formation in plant cells while the relationship between plant surface areas and N₂O 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 N₂O even at field conditions and challenge a view that plants are a medium to transport soil-produced N₂O into the atmosphere.

Keywords: (15)N site preference; N(2)O; Natural source; Plant emission; Respiration; Soil emission.