The influence of pyroligneous acid on fermentation parameters, CO2 production and bacterial community of rice straw and stylo silage

CO2 is known as a primary greenhouse gas and the main cause of global warming. It could be produced during ensiling, a method of moist forage preservation applied all over the world, because of respiration of plant cells and microorganisms. However, limited information about CO2 emission and mitigation during ensiling is available. Pyroligneous acid, a by-product of plant biomass pyrolysis, has strong antibacterial capacity. To investigate the CO2 production and the influence of pyroligneous acid, fresh stylo and rice straw were ensiled with or without 1% and 2% pyroligneous acid. The dynamics of fermentation characteristics, CO2 production and bacterial community during ensiling were analyzed. Results indicated that pyroligneous acid increased (P < 0.05) lactic acid content and decreased (P < 0.05) weight losses, pH value, ammonia-N, butyric acid contents and coliform bacteria number. It also increased the relative abundance of Lactobacillus and decreased that of undesirable bacteria like Enterobacter and Lachnoclostridium. The addition of pyrolytic acids reduced gas production, especially CO2 production. It increased the relative abundance of CO2 producing genera and increased that of genera with potential for CO2 fixation. In conclusion, the fermentation quality of these two silages was improved by adding pyroligneous acid. During ensiling, CO2 production correlated with bacterial community. Using pyroligneous acid could alter bacterial community to reduce CO2 production during ensiling. Given the huge production and demand for silage around the world, the application of pyroligneous acid could be an effective way to mitigate global warming by greenhouse gas emission.

二氧化碳（CO₂）是公认的首要温室气体，亦是全球变暖的主要诱因。其可在青贮发酵（ensiling）过程中产生——该工艺为全球范围内广泛应用的湿润饲草保存方法，依托植物细胞与微生物的呼吸作用完成。然而，当前关于青贮发酵过程中二氧化碳排放与减排的相关研究资料较为匮乏。木醋液（pyroligneous acid）作为植物生物质热解的副产物，具备优异的抗菌性能。为探究青贮发酵过程中的二氧化碳生成量及木醋液的调控作用，本研究以新鲜柱花草与稻草为原料，分别添加1%、2%浓度的木醋液进行青贮发酵，并设置未添加的对照组。研究对青贮发酵过程中发酵特性、二氧化碳生成量及细菌群落的动态变化进行了系统分析。结果显示，添加木醋液可显著提升青贮饲料的乳酸含量（P < 0.05），同时显著降低饲料减重率、pH值、氨态氮含量、丁酸含量及大肠菌群数量（P < 0.05）。此外，木醋液可提高乳杆菌属（Lactobacillus）的相对丰度，降低有害菌如肠杆菌属（Enterobacter）与拉氏梭菌属（Lachnoclostridium）的相对丰度。添加木醋液可减少青贮发酵过程中的气体生成量，尤以二氧化碳生成量的削减效果最为显著。该处理同时提升了产二氧化碳类群的相对丰度，并增强了具备二氧化碳固定潜力类群的相对丰度。综上，添加木醋液可改善两种青贮饲料的发酵品质。青贮发酵过程中，二氧化碳生成量与细菌群落结构密切相关。施加木醋液可通过调控细菌群落结构，降低青贮发酵过程中的二氧化碳生成量。鉴于全球范围内青贮饲料的产量与需求量均极为可观，应用木醋液可通过减少温室气体排放，成为缓解全球变暖的有效途径之一。