Effects of straws on greenhouse gas emissions in the ectopic fermentation system

Straws are commonly used padding materials in the ectopic fermentation system, but their effects on greenhouse gas emissions are not well understood. This study compared the effects of rape, rice and corn straws on the fermentation performance of the ectopic fermentation system. Compared with corn straw, the treatment groups with rape straw and rice straw significantly increased the alpha diversity of the fermentation system, and simultaneously mitigated the cumulative emissions of CO₂ and N₂O by up to 32.4% and 93.9%, respectively. The CO₂ and N₂O peak emission in the treatment group with corn straw reached 1.4 × 10⁶ and 36.2 mg/m²/d, respectively. CH₄ peak emission was one order of magnitude lower than that of N₂O in the ectopic fermentation system. Redundancy analysis showed that Pseudoxanthomonas sp000510725 was the key specie that positively affect the fermentation temperature, CO₂ and N₂O emissions in the fermentation system. Nitrogen metabolism genes, such as nosZ, nirK, and nirS were more abundant in the surface layer of the fermentation system, indicating more active nitrogen metabolism in this region, and the core zone could be the primary source of N₂O emissions. Those findings indicated that rape and rice straw can be potential padding materials for mitigating greenhouse gas emissions in large-scale ectopic fermentation system.