Gypsum Application and Straw Incorporation Interact to Alleviate Methane Emissions in Coastal Saline-Alkali Rice Soils

Enhancing the management of saline-alkali lands can expand the area of crop cultivation. Gypsum application and straw retention are widely adopted practices to mitigate soil salinization and boost soil fertility in saline-alkali lands worldwide, but their combined effects on methane (CH₄) emissions remain unclear. We conducted a pot experiment to investigate how the application of flue gas desulfurization gypsum and wheat straw incorporation affects CH₄ emissions in coastal saline-alkali paddies. There were 4 treatments including no straw incorporation or gypsum application, gypsum application without straw incorporation, straw incorporation without gypsum application, and straw incorporation combined with gypsum application. Straw incorporation significantly increased seasonal CH₄ emissions by an average of 9.7 times compared to straw absence, through the increase in the dissolved organic carbon and abundance of mcrA gene. However, gypsum application substantially decreased CH₄ emissions by 74.8% relative to no gypsum application. Gypsum application reduced mcrA gene abundance and increased the abundance of pmoA, dsrA, and dsrB genes, suggesting a suppression of CH₄ production and a promotion of CH₄ oxidation. Gypsum application-induced reduction in CH₄ emissions was greater under straw incorporation (-76.6%) than under straw absence (-54.9%). Gypsum application boosted the abundance of pmoA and dsrB genes more strongly under straw incorporation than under straw absence. The application of gypsum had a large potential to mitigate CH₄ emissions resulting from straw incorporation in coastal saline-alkali rice fields, thereby mitigating climate warming and enhancing soil fertility.