Exchange of carbonyl sulfide (OCS) and dimethyl sulfide (DMS) between rice paddy fields and the atmosphere in subtropical China

Abstract

Carbonyl sulfide (OCS) and dimethyl sulfide (DMS) are important trace gases contributing to sulfate aerosol formation in the lower and upper atmosphere and hence greatly impacting global radiative balance. In the present study the exchange of OCS and DMS between rice ( Oryza sativa L.) paddy fields and the atmosphere was studied in subtropical China from November 2004 to July 2005. OCS and DMS fluxes were compared between the planted and non-planted paddy fields, and between dry and waterlogged soils. The rice paddy fields were found to be a net sink for OCS and a source for DMS, with an uptake rate of 12.1 ± 16.0 pmol m −2 s −1 for OCS and an emission rate of 25.9 ± 35.2 pmol m −2 s −1 for DMS. OCS fluxes varied significantly between non-planted dry and waterlogged soils, with an uptake rate of 11.4 ± 7.1 pmol m −2 s −1 for non-planted dry soils and an emission rate of 9.0 ± 5.4 pmol m −2 s −1 for non-planted waterlogged soils. For DMS the variation between non-planted dry and waterlogged soils was not significant. Both OCS and DMS fluxes showed significant differences between the planted and non-planted waterlogged soils. For OCS, the planted waterlogged soil acted as a sink with an uptake rate of 29.0 ± 25.7 pmol m −2, but the non-planted waterlogged soil acted as a source with an emission rate of 9.0 ± 5.4 pmol m −2 s −1. For DMS, both the planted and non-planted waterlogged soils acted as sources, with an emission rate of 51.2 ± 37.5 pmol m −2 s −1 for the planted waterlogged soil, which was significantly higher than that for the non-planted waterlogged soil (3.8 ± 2.8 pmol m −2 s −1). OCS and DMS exchange rates differed significantly at different rice growth stages, with the highest fluxes at the jointing-booting stage. The potential factors causing the variations between the different treatments are also discussed. This work revealed that rice paddy field in subtropical China acts as a sink for OCS and an emission source for DMS as a whole and further investigation on the influence of soil microorganisms and soil redox potential on the OCS and DMS fluxes in rice paddy field are needed.