Effect Of Livestock Dung Type On Nitrous Oxide In Different Degraded Grassland

Nitrous oxide?N₂O?is an important greenhouse gas affected by human activities.Since the 18 th century,the concentration of N₂O in the atmosphere has increased by nearly 20%.The increase in N₂O concentration not only aggravates greenhouse effect,but also indirectly destroys the ozone layer and enhances the ultraviolet radiation that reaches the earth's surface,endangering the health and safety of human beings,animal and plant.The grazing livestock excreta plays an important role in N₂O emission.It can affect the activity of microorganisms by changing the physical and chemical properties of soil and plant characteristics,and finally influence N₂O emission.However,there are few studies on livestock excreta on greenhouse gas emissions in China,and the existing studies mainly focus on the effect of dung composting on greenhouse gas emissions.Most of the experimental subjects about the effects of excrement on greenhouse gas release use cattle dung,cattle urine or synthetic urine,ignoring the importance of sheep dung on N₂O emission,resulting in a lack of research on comparing the effects of cattle and sheep dung on N₂O emission at the same time.In addition,due to long-term unreasonable grazing,large areas of grassland in China have degraded to varying degrees,manifested by changes in the composition of grassland vegetation,soil habitat degradation,and productivity decline.Change in these factors may affect the activity of soil microorganisms and thus affect the N₂O emission.However,few studies have examined the effects of dung from different grazing livestock species on N₂O emissions on grassland different degradation.In this study,static box method and LGR nitrous oxide analyzer were used to study the soil N₂O emission characteristics of different types of livestock excreta?cattle dung,sheep dung?and different types of vegetation patches at Songnen Grassland Ecological Station of Northeast normal University from June to September in 2019,so as to explore the effect of different livestock dung?cattle dung,sheep dung?on N₂O emission in three plant community patches and clarify the main factors affecting livestock dung in N₂O emission.The study is important for researchers to further understand the greenhouse gas emission effects of grassland grazing ecosystem and to formulate reasonable grazing policies to control greenhouse gas emissions.The results are as follows:1)The effect of cattle dung on grassland N₂O flux does not depend on grassland degradation degree,and the addition of cattle dung significantly increased N₂O emission flux in the three plant community patches.2)The effect of sheep dung on grassland N₂O flux significantly depended on grassland degradation gradient.In lightly and heavily degraded grassland,the addition of sheep dung significantly increased grassland N₂O flux,while had no effect in non-degraded grassland.3)The effect of livestock dung type?cattle dung,sheep dung?on grassland N₂O flux was significantly different,and does not dependent on the grassland degradation.The N₂O flux of cattle dung treatment was significantly higher than that of sheep dung treatment in three degraded grassland patches.4)The N₂O emission flux also differed among three degraded grassland patches,and depended on the type of livestock dung.Under cattle dung and control treatments,there were no significant difference in N₂O flux in three plant community patches.However,under the sheep dung treatment,the N₂O flux emitted by lightly degraded grassland patches was significantly higher than that of non-graded and heavily degraded grassland patches.5)Livestock dung type affect N₂O emission by changing soil temperature,soil moisture and plant aboveground biomass.The interactive effects of livestock dung and grassland degradation on N₂O emission flux were mainly manifested in the early stage of N₂O emission.In conclusion,the N₂O emission flux of grassland ecosystem strongly depended on the dung type of different grazing livestock and grassland degradation.The dung from cattle grazing brought more serious influences on N₂O emission.Our study also indicated that livestock grazing will pose greater threat to green house gas emission by animal excreta return in the process of grazing with the increasing grassland degradation in China.