Relationship Between Yak Grazing Intensity And Vegetation And Soil Characteristics In Gannan Alpine Meadow

Grazing affects the ecological processes of grassland vegetation and soil,and play an important role on the dynamics of plant communities.In order to better understand the key biological factors of livestock-soil-plant interactions,and the ecological mechanisms and processes of population regenerationunder grazing system in the alpine grassland,current experiment was carried out on three farms at different grazing intensities,in close proximity to each other,there were located in Animal husbandry science and technology demonstration park of Maqu county in the northeast edge of Qinghai-Tibet Plateau,Gannan Tibetan area.According to the number of herding yaks,distance from the farmer's shed,the activity route of yak's selective feeding and the intensity of herding activities during the frequency of stay,a transect sampling design along the grazing gradient was chosen to establish a grazing gradient with increasing distance from a poultry ring,the site surrounding each poultry ring was stratified into three concentric levels.From near to far to the entrance of the poutry ring,we set light,moderate,and high grazing intensity.To investigate the effects of grazing intensity,we analyzed the vegetation and soil characteristics and the livestock-soil-plant interactions,the main results were as follows:1)At the same year,the aboveground and belowground biomass significantly decreased with yak grazing intensity incresed(P<0.05).Under the different years in the same grazing intensity level,aboveground biomass was higher in 2016 than that in 2017,but the underground biomass showed the opposite result.Total biomass of 2 years had no significant changes under the same grazing intensity.And changing with the growth rhythm of forage from June to September,the biomass was the highest in August,which was 436.27 g/m ~2 in 2016 and 370.36 g/m ~2 in 2017,respectively.2)Plant species diversity shows,the Shanoon index and the Margalef richness index declined as the increase of grazing intensity(P<0.05).Pielou index and Simpson index,which was affected differently by grazing intensity between 2016 and 2017.3)Grazing intensity had a certain impact on the forage quality,but there was no significant difference among treatments(P>0.05).Compared with the control,yak grazing intensity significantly increased the content of crude protein(CP)(P<0.05)and decreased the content of neutral detergent fiber(NDF)(P<0.05)in 2017.4)Grazing intensity significantly decreased the surface soil water content and organic carbon(SOC)at 0-10 cm depth(P<0.05).Soil pH value increased with grazing intensity increase,but the total nitrogen content showed a decrease trend,and the grazing intensity decreased the soil carbon and nitrogen ratio.5)The correlation analysis showed that the soil water content has a significant positive relationship with organic carbon,total nitrogen and nitrate nitrogen content at 0-10 cm depth,but had a significant negative relationship with soil pH.There were no significant correlation between available phosphorus and available potassium.Meanwhile,soil organic carbon had a significant positive correlation with total nitrogen,available phosphorus and available potassium content.6)According to the PCA,grazing,soil organic carbon,total nitrogen and soil water content(SW)were the main factors for the aboveground biomass(Ab).And the Simpson index(Si)was the main factor affecting underground biomass(Ub).Ab was negatively correlated with CP and crude ash(Ash)content,and Ub was negatively correlated with Shanoon diversity index,Pielou evenness index and Margalef richness index.In addition,grazing had no significant effect on crude fat(EE).