Straw return enhances the global warming potential in paddy soil under the regulation of functional genes

Straw return enhances soil carbon storage but raises concerns over greenhouse gas (GHG) emissions. This study examined the impact of milk vetch (ZYY), wheat (XM), and rape (YC) straws on GHG emissions from paddy soils via incubation experiment. The dynamics of functional genes and bacterial communities were analyzed. Results indicated that straw addition significantly increased total organic carbon (TOC) by 51.7 %–70.4 % and dissolved organic carbon by 318.5 %–445.1 %, compared to CK. This led to elevated CO₂ and CH₄ emissions but reduced N₂O emissions. The XM treatment showed the highest global warming potential (GWP), 53.4 % and 25.0 % higher than ZYY and YC, respectively. TOC and soil microbial biomass nitrogen explained 6.8 % of CO₂ and 8.0 % of N₂O emissions. Straw addition also intensified the citrate cycle and pentose phosphate pathway, further promoting CO₂ emissions. The gene mcrA was the primary factor influencing CH₄ emissions, with Ignavibacteriae and Anaerolinea identified as its main hosts. Straw addition likely suppressed N₂O emissions by regulating denitrification-related species (e.g., Anaeromyxobacter, Geobacter). N₂O emissions were also influenced by mcrA, pmoA, and their hosts, potentially linked to anaerobic ammonium oxidation. This study offers insights into straw's effects on GHG emissions through functional gene and microbial regulation in paddy soils.