Straw incorporation mitigates methane emissions by facilitating the conversion of particulate organic carbon to mineral-associated organic carbon

Abstract

Incorporating straw return into tillage systems is a potential strategy for sustaining rice production, while achieving multiple environmental benefits. The effect of different tillage management on methane emissions has been well documented; however, the combined effects with straw return management require further exploration. To investigate this, an experiment was initiated in 2008 using five management practices: conventional tillage, no tillage, conventional tillage with straw mulching, conventional tillage with straw incorporation, and no tillage with straw mulching. Changes in soil carbon pool properties, hydrolytic and oxidative enzyme activities, phospholipid fatty acids, and the abundance of methanogenic and methanotrophic genes were measured during the early and late rice-growing seasons in 2022 and 2023. The results indicated the following: (1) Straw return significantly increased cumulative methane emissions by 75.5 % compared with straw removal. However, conventional tillage with straw incorporation reduced cumulative methane emissions by 37.2 % and 20.3 % compared to conventional tillage with straw mulching and no tillage with straw mulching, respectively. (2) Conventional tillage with straw incorporation enhanced β-acetylglucosaminidase and cellobiohydrolase activities and increased mineral-associated organic carbon content compared to conventional tillage with straw mulching and no tillage with straw mulching. (3) Under conventional tillage with straw incorporation, the content of phospholipid fatty acids in bacteria, fungi, and actinomycetes increased by 7.6 %–19.3 %, 7.2 %–18.3 %, and 6.0 %–19.8 % compared with conventional tillage, no tillage, and conventional tillage with straw mulching, respectively. (4) Conventional tillage with straw incorporation reduced methanogens/methanotrophs by 14.1 % and 4.0 % compared with conventional tillage with straw mulching and no tillage with straw mulching, respectively. Structural equation modeling revealed that tillage and straw management promoted the conversion of particulate organic carbon to mineral-associated organic carbon by increasing the soil microbial populations and β-acetylglucosaminidase and cellobiohydrolase activities, which regulated methane production by methane-related functional communities. Thus, regulating the conversion of activated carbon to inert carbon through a rational combination of tillage and straw return methods can effectively reduce methane emissions from double rice paddies.