Unraveling the fascinating connection between hydrochar feedstock and methane emissions in rice paddy soil: Insights from microorganisms and organic matter

Despite the increasing attention given to hydrochar as a soil improver, its impact on methane emissions in paddy soil remains unclear, particularly with regard to the use of hydrochar derived from different feedstocks. In this study, four types of hydrochar (rice straw, corn straw, poplar wood, and enteromorpha) were added to paddy soil. The addition of rice straw hydrochar had no significant effect on meathane emissions. However, corn straw and poplar wood hydrochar increased methane emissions by 17.78% and 18.68% respectively. In contrast, enteromorpha hydrochar reduced methane emissions by about 20.21%. These variations were attributed to differences in organic matter released by the hydrochar, influencing microbial community composition and activity. The inhibitory effect of Enteromorpha hydrochar on methane production are closely related to its high ash content and enrichment of Candidatus_Nitrososphaera, Acinetobacter, Flavobacterium, and Rhodoplanes, associated with nitrification and denitrification. On the other hand, corn straw and poplar wood hydrochar promoted methane production through the enrichment of Geobacter, Anaerolinea, and Anaeromyxobacter, probably facilitating direct interspecies electron transfer with Methanosarcina. These findings underscore the significance of evaluating various hydrochar feedstocks for effective management of methane emissions in paddy soil.