Effects of elevated CO 2 and N fertilization on CH 4 emissions from paddy rice fields

The authors employed free‐air carbon dioxide enrichment facilities for investigating the effects of elevating the present atmospheric CO 2 by 200 μmol mol −1 and increasing the application rate of urea‐based fertilizers from 150 to 250 kg N ha −1 on CH 4 emissions from paddy rice fields in southeastern China. The elevated CO 2 significantly stimulated methane emission, which was mainly due to the stimulation in rice growth. Intensifying N fertilization mitigated the CH 4 emission under the ambient CO 2 but stimulated the CH 4 emission under the elevated CO 2 . This suggests that N fertilization has a potential to stimulate both CH 4 production and CH 4 oxidation. Thus the net effect of N fertilization on CH 4 emission from paddy rice fields most likely depends upon the counterbalance between the nitrogen‐induced increases in CH 4 production and CH 4 oxidation, as a N excess may result in the inhibition of methane emission, whereas a N limitation may result in the stimulation of methane emission.