Seasonal Dynamics Of Condensed Tannins In Typical Alpine Plants And Its Application Inhibition Of Methane Emission From Yak Rumen

Alpine grassland plays an important role in maintaining ecosystem stability and national ecological security on the Qinghai-Tibet Plateau.However,the imbalance of the seasonal supply of forage grass in the natural grassland on the Qinghai-Tibet Plateau has become a key factor restricting the production potential of grazing livestock.Therefore,a comprehensive evaluation of the nutritional value of alpine plants and the effects of phenolic substances in alpine shrubs on livestock could provide theoretical reference for the rational development and utilization of other grassland resources.In this experiment,the seasonal variation of nutrient components and phenolic substances in 21 typical alpine plants（mainly shrubs）in the Jinqiang River Basin of East Qilian Mountains was studied.The effects of alpine shrub leave rich in condensed tannins on rumen fermentation characteristics,methane production,and microorganisms of yaks were evaluated by in vitro fermentation technology.1.The DM content of 21 dominant alpine plants belonging to 12 different families,such as Ericaceae Juss.,Rosaceae,Leguminosae sp.,and Salicaceae Mirb.,showed a"V"shape change with plant maturity.Except forRosaceae,the DM content of all the alpine plants was the lowest in August.Crude protein content in plants decreased significantly with seasonal changes（P<0.05）,the contents of NDF and ADF were significantly increased with seasonal changes（P<0.05）,Crude ash content had no seasonal variation.2.The variation of phenolic content had obvious seasonal and species characteristics.The seasonal variation of total phenolic content of plants in the same family was similar,but the phenolic content of shrub plants was significantly higher than that of herb plants（P<0.05）.Total phenols and tannins varied in a wavy or inverted"V"shape with the seasons,and there were significant differences among different plants（P<0.05）.The content of condensed tannin decreased gradually with the passing of season,and the lowest in October（P<0.05）with an average of 11.19 g/kg DM.Comprehensive analysis showed that the content of condensed tannin in shrub plants was significantly higher than that in other plants（P<0.05）with an average of 42.29 g/kg DM and 36.96 g/kg DM,respectively.From the biological characteristics of condensed tannin,it can be used as a potential dominant shrub for subsequent in vitro fermentation research.3.The results of in vitro fermentation showed that CT content in plants had significant effects on in vitro gas production and methane production（P<0.05）,the total gas production in vitro of Salix cupularis was higher than that in Hippophae tibetica（P<0.05）;At the same time,both shrubs significantly reduced methane production,and there was a negative correlation between CT content and methane production（P<0.05）,and compared with the control group,the methane production was reduced by 22.0%and 27.53%,respectively,by Salix cupularis and Hippophae tibetica.The IVDMD and IVND of Salix cupularis were significantly higher than those of Hippophae tibetica（P<0.05）,and the contents of IVGP,IVND and CT at 24h were significantly negatively correlated（P<0.05）.pH and NH₃-N decreased gradually with the increase of CT content in plants.Acetic acid,butyric acid,and ethyl acid/propionic acid decreased with the increase of CT content,but the propionic acid content increased gradually.4.According to the high-throughput sequencing analysis of 16S rRNA of microorganisms in the in vitro fermentation system,Bacteroidetes accounted for the highest proportion of 60.20%～63.70%in the rumen fermentation samples with Salix and Hippophae rhamnoides as substrates in different seasons,followed by Firmicutes and Protebacteria.In the samples of different seasons,the Shannon index of two species of plant bacteria decreased significantly in July（P<0.05）,but there was no significant change in Chao1 index（P>0.05）.Among the archaea,the dominant ones are Euryarchaeota and Thaumarchaeota.The Shannon index of Archaea decreased with the increase of CT content in plants（P<0.05）,there was no significant change in Chao1 index（P>0.05）.Correlation analysis further showed that the relative abundance of Methanosphaera was significantly positively correlated with CH₄production in vitro（P<0.01）,indicating that CT in plants could regulate methane production by affecting the abundance of rumen Methanosphaera.