『Abstract
　Here we report on a controlled environment experiment in which we applied ¹³C- and ¹⁵N-enrichment approaches to quantify methane oxidation rates and source partition N2O production in a silt loam soil following application of NH4NO3, enabling us to look for potential interactions between methane oxidation and nitrifier-N2O production. ¹⁵N-N2O, ¹⁴⁺¹⁵N-N2O and CO2 fluxes and mineral N concentrations were measured over a 23-day period after application of NH4NO3 (5 at.％ excess ¹⁵N) at rates of 0, 5, 10, 20, 30 and 40 g N m^-2 to a silt loam soil. Change in ^12/13C-CH4 concentrations (as indicative of ¹³C-CH4 oxidation rates) and production of ¹³C-CO2 were monitored over the first 72 h after addition of 1.7 μl ¹³C-CH4 l^-1 (10 at.％ excess ¹³C) to these N treatments. Oxidation of applied ¹³C-CH4 was slower in the 5, 10, 20 and 30 g N m^-2 (5 at.％ excess ¹⁵N) treatments (0.24-0.32 μg ¹³C-CH4 l^-1 day^-1) than in the control (0.40 μg ¹³C-CH4 l^-1 day^-1), suggesting that these N loadings inhibited oxidation. N2O production was raised after N addition, and in the 10, 20 and 30 g N m^-2 treatments nitrification was the predominant source of N2O accounting for 61, 83 and 57％ of the total ¹⁵N-N2O produced, respectively. Our results point towards the possibility of methylotrophs switching function to oxidise ammonia in the presence of N, which may result in greater atmospheric loading of both CH4 and N2O.

Keywords: Denitrification; Methane oxidation; Nitrification; Nitrous oxide; Soil; Stable isotopes』

Introduction
Materials and methods
　Experimental set-up
　Gas sampling and analysis
　Soil sampling and analysis
　Statistical analysis
Results
　Methane oxidation and N2O production over the first 72 h
　Nitrous oxide and CO2 production over the 23-day experimental period
　Source partitioning of ¹⁵N-N2O　
　Soil mineral N
Discussion
　CH4 oxidation rates in response to N application
　A ¹³C approach for determining CH4 oxidation rates
　Microbial source of N2O with increasing N application
　Possible interactions between CH4 oxidation and nitrifier-N2O production
Conclusions
Acknowledgements
References