Fig. 5. Multiple-isotope signatures of N₂O illustrating the relative contributions of bacterial denitrification (BD), fungal denitrification (FD), and chemodenitrification (CD) in the plastisphere and bulk water.

a Relationships between N₂O-SP and N₂O-δ¹⁸O (N₂O/H₂O) values in each group. N₂O-δ¹⁸O values were corrected for H₂O-δ¹⁸O assuming almost complete O exchange. Ranges of putative isotope signatures of N₂O (δ¹⁸O (N₂O/H₂O)) from BD, FD, and CD are indicated as the three color boxes. The corresponding references are listed in the figure. The area enveloped by gray dash lines represents the N₂O reduction through BD process based on fractionation effects (slope=SP_εN2O/δ¹⁸O_εN2O = 0.25). This mapping approach is modified from the method in ref. ⁸³. b Relative proportions of N₂O production via BD, FD, and CD in the plastisphere and bulk water. Errors were estimated by Monte Carlo simulation and reflected the accuracy of N₂O isotope mass balance model. Although the contributions of each denitrification process would shift with the prescribed extent of oxygen change and N₂O-SP and N₂O-δ¹⁸O values, all ranges suggest that biotic denitrification instead of chemodenitrification was the main contributor to N₂O production in the plastisphere and bulk water.