Abstract: [Objective] This study was conducted to assess the effects of adding lactic acid bacteria and sugars on fermentation weight loss, fermentation quality and microbial community structure of wheat straw yellow storage at different compaction densities. [Method] Wheat straw was crushed into proper length and the initial moisture content was adjusted to 60%. After well mixing, it was randomly divide into two equal parts. One part was supplemented with the additives composed of a commercially available microbial agent containing 1×10⁵ CFU/g of Lactobacillus plantarum （5 g/t） and white sugar （10 kg/t）, evenly sprayed with 3% sterile water, and then compacted to prepare yellow storage at the densities of 450, 500 and 550 kg/m³ （additive treatment group）, respectively. The other part was evenly sprayed with 3% sterile water, and then compacted to prepare yellow storage at the densities of 450, 500 and 550 kg/m³ （control group）, respectively. Fermentation weight loss of the yellow storage of the two groups with different compaction densities were measured after fermentation for 1, 3, 6, 15, 35 and 200 d, respectively. At 200 d of fermentation, the yellow storage samples were taken to assess the fermentation quality, microbial quantity and microbial diversity. [Result] From 3 d to 200 d of fermentation, the fermentation weight loss of both groups increased significantly （P<0.05）. At 35 d and 200 d of fermentation, the fermentation weight loss of the additive treatment group was significantly （P<0.05） lower than that of the control group. Compared with the control group, the additive treatment group had significantly （P<0.05） lower pH value, significantly （P<0.05） higher lactic acid content, significantly （P<0.05） reduced ammoniacal nitrogen content, and significantly （P<0.05） elevated acid-base buffering capacity. The number of lactic acid bacteria and yeasts of the additive treatment group was significantly （P<0.05） lower than that of the control group. Lactiplantibacillus and Lentilactobacillus were found as the dominant bacterial genera in both groups, with relative abundance of 22.12%-49.18% and 1.45%-49.91%, respectively, and their total relative abundance exceeded 34.25%. At the compaction density of 450 kg/m³, the relative abundance of Leuconostoc and Enterobacter of the additive treatment group was significantly （P<0.05） lower than that of the control group. At the compaction density of 500 kg/m³, significantly （P<0.05） lower relative abundance of Lentilactobacillus and Leuconostoc as well as significantly （P<0.05） higher relative abundance of Enterobacter, Pantoea, Ralstonia and Weissella were observed in the additive treatment group compared with the control group. At the compaction density of 550 kg/m³, the additive treatment group had significantly （P<0.05） decreased relative abundance of Lentilactobacillus, Enterobacter and Leuconostoc as well as significantly （P<0.05） increased relative abundance of Bacillus and Paenibacillus than the control group. The relative abundance of Lentilactobacillus was negatively correlated with lactic acid content, the ratio of lactic acid to acetic acid, and acid-base buffering capacity （P>0.05）, positively correlated with acetic acid content （P>0.05）, significantly （P<0.05） positively correlated with pH value, and significantly （P<0.01） positively correlated with ammoniacal nitrogen content. The relative abundance of Enterococcus and Lactococcus was significantly （P<0.05） negatively correlated with lactic acid content, significantly （P<0.01） negatively correlated with the ratio of lactic acid to acetic acid as well as acid-base buffering capacity, and significantly （P<0.01） positively correlated with pH value. The number of lactic acid bacteria and yeasts was significantly （P<0.01） positively correlated with pH value and ammoniacal nitrogen content, and significantly （P<0.01） negatively correlated with the ratio of lactic acid to acetic acid. [Conclusion] Increasing compaction density and utilizing microbial additive can reduce the fermentation weight loss and ameliorate the fermentation quality of wheat straw yellow storage.

Key words: lactic acid bacteria additive, compaction density, wheat straw yellow storage, microbial community structure, fermentation quality