Effects of lactic acid bacteria type and ambient temperature on fermentation quality and greenhouse gas emissions of oat forage silage

The global livestock sector produces enormous greenhouse gas (GHG) emissions with substantial mitigation potential, yet the emissions of CO 2 , CH 4 , and N 2 O released during silage production through microbial fermentation, along with the associated losses of dry matter and energy, remain insufficiently studied. Oat is an important forage crop on the Qinghai-Tibet Plateau, and its silage fermentation is significantly influenced by ambient temperature and lactic acid bacteria type (homofermentative vs. heterofermentative); however, the mechanisms by which different LAB types regulate GHG emissions and their differential responses to temperature are still poorly understood. This study investigated the effects of different lactic acid bacteria (LAB) inoculants and ambient temperatures on the fermentation quality, aerobic stability, greenhouse gas (GHG) emissions, and bacterial community of oat forage silage. The results showed temperature and inoculant showed significant interactions on pH at days 7 and 60, and on acetic and propionic acid at day 19 ( P < 0.05). Lactiplantibacillus plantarum 260 (LP) consistently resulted in the lowest pH and highest lactic acid content, indicating optimal fermentation quality. Lentilactobacillus buchneri 40,788 (LB) increased acetic acid but maintained a higher pH, consistent with typical heterofermentative metabolism. Low temperature enhanced lactic acid production in LP-treated silage, whereas high temperature intensified heterofermentation in LB-treated silage. LB significantly improved aerobic stability, as evidenced by the smallest rise in core temperature after 168 h of aerobic exposure. CH 4 was detected only in the high-temperature CK group during early fermentation and CH 4 was below the detection limit in all LAB-treated groups. LB may increase N 2 O during the early stage at low temperature and CO 2 at high temperature, whereas LP maintains relatively low N 2 O and CO 2 under both temperature conditions. CO 2 emission occurred throughout the ensiling process; LB led to higher initial CO 2 emissions due to heterofermentation, while LP resulted in the lowest CO 2 emissions. Regarding bacterial community, LP increased the relative abundance of L. plantarum from 40 to 55%, while LB raised L. buchneri abundance to nearly 95%. Low temperature favored the enrichment of L. plantarum , whereas high temperature increased spoilage-associated bacteria such as Clostridium and Bacillus. Correlation analysis revealed that L. plantarum was positively correlated with lactic acid and negatively correlated with pH and propionic acid. In contrast, L. buchneri was positively correlated with acetic acid. CH 4 , N 2 O, and CO 2 emissions were positively correlated with genera such as Leuconostoc and Enterobacteriaceae . CO 2 is the primary GHG emitted during oat silage fermentation. LP rapidly acidifies the silage, improves fermentation quality, and reduces GHG emissions. LB enhances aerobic stability but may increase CO 2 and N 2 O emissions under high-temperature conditions.