Effects of elevated temperature and atmospheric carbon dioxide concentration on the emissions of methane and nitrous oxide from Portuguese flooded rice fields

Abstract Methane (CH 4 ) and nitrous oxide (N 2 O) emissions from flooded rice fields have been rarely measured in Europe. A field study was carried out in an intermittent flooded rice field at central Portugal to investigate if global warming under Mediterranean conditions, elevated soil temperature (+2 °C) and atmospheric [CO 2 ] (550 ppm), could lead to significant effects in CH 4 and N 2 O emissions. The experimental design consisted of three treatments arranged in a randomized complete block design with three replicates. To assess the effects of ambient temperature and actual atmospheric [CO 2 ] (375 ppm), plots were laid under open-field rice conditions. Using open-top chambers, two other treatments were established: one to assess the effect of elevated temperature and actual atmospheric [CO 2 ] and a third treatment to evaluate the combined effect of elevated temperature and atmospheric [CO 2 ]. Measurements of CH 4 and N 2 O fluxes were made throughout two consecutive growing seasons in the field using the closed chamber technique. Elevation of temperature with or without elevated atmospheric [CO 2 ] increased CH 4 emissions by 50%, but this increase was not significant compared to the open-field condition. As for N 2 O, elevated temperature alone or combined with elevated atmospheric [CO 2 ] had no significant effect on emissions relative to the open-field treatment. The estimated seasonal CH 4 EF for the Portuguese flooded rice fields was 10.0 g CH 4  m −2 , while the EF for N 2 O emissions was 1.4% of N input. These results suggested that default seasonal CH 4 and N 2 O EFs currently used by the Portuguese inventory were not appropriated.