Changing Greenhouse Gas Emissions from Flooded Rice Paddies Under Projected Future Climates.

Rice paddies are a major contributor to greenhouse gas emissions, especially methane and nitrous oxide that have 20 to >300 times the effect, respectively, of carbon dioxide on a per molecule basis. With an increasing demand (and need) for rice, it is important to understand whether and to what extent greenhouse gas emissions from rice paddies will be altered with a changing climate.

We performed paddy soil incubations under today’s climate and the postulated climate of the year 2100 for Californian and Cambodian rice-growing regions. Additional incubations were used to determine the effect of either just elevated temperature or just elevated atmospheric CO₂ on greenhouse gas emissions. Our data indicates that a rapid transition of 5°C higher temperatures affects nitrous oxide and methane production drastically, whereas doubled atmospheric CO₂ stimulates methane and nitrous oxide emissions. Overall, the effect of temperature on greenhouse gas emissions is more pronounced than changes in atmospheric CO₂, leading to significantly different greenhouse gas emissions from rice paddies in the future. The observed atmospheric data are further budgeted with data for water-extractable and solid phase carbon and nitrogen, and they are correlated to other plant nutritional elements of the soil. The changes in greenhouse gas emissions are explained by tracking the abundance and activity of the soil microbial community with 16S rRNA gene and transcript qPCR, respectively.

The study provides a better understanding of the role rice paddies will play for global greenhouse gas emissions in the future. In conjuction with this, quantifying the type of carbon, nitrogen, and other elements in paddies can be used to assess the health of paddy soils to confidently estimate rice productivity in the future.