Changes in greenhouse gas evolution in heavy metal polluted paddy soils with rice straw return: A laboratory incubation study

• Pollution reduced straw C mineralization and changed proportion of CH4 and CO2.
• Soil and straw pollution increased the N2O evolution with straw return.
• Metal pollution in soil or straw enhanced the overall global warming potential.

Heavy metal pollution in rice paddies has been known to alter soil microbial biomass, diversity and, in turn, the processes mediating soil biogenic greenhouse gas evolution. However, there has been poor knowledge of potential changes in greenhouse gas evolution with rice straw return from polluted rice paddies. In this study, a 90-day lab incubation experiment under anaerobic condition was conducted to track changes in CO2, CH4 and N2O evolution from heavy metal polluted paddy soil with polluted rice straw return, compared to from unpolluted soil with unpolluted straw return. Our results showed that the total CO2 and CH4 evolution from polluted soil incorporating polluted straw were decreased by 21% and 79%, respectively compared to unpolluted straw amended in unpolluted soil. Compared to unpolluted straw, the total carbon mineralization of metal polluted straw was reduced by 13% and 34% in unpolluted and polluted soils, respectively and metal pollution changed the proportion of CH4 and CO2 to total straw carbon mineralized. Though there was a generally reduction of N2O evolution with straw amendment, the total N2O evolution was increased by 190% in unpolluted soil and by 352% in polluted soil with polluted straw amendment compared to with unpolluted straw. The overall global warming potential (GWP) increased significantly by 31% and 58% with polluted straw amendment in unpolluted and polluted soils, respectively compared to with unpolluted straw. Therefore, metal pollution both in soil and straw resulted in a slow carbon mineralization but a high N2O evolution, and then enhanced the overall GWP in metal polluted rice paddies with rice straw return. The increased GWP would pose a risk to soil carbon sequestration in metal polluted paddy field.