Soil Carbon And Nitrogen Mineralization In The Eastern Eurasia Steppe Transect And Its Response To Grazing

With the current intensification of human activities and the increasing concentration of greenhouse gases in the atmosphere,issues such as the cycling of carbon and nitrogen are one of the hotspots of global change research.The Eurasian grasslands in the middle and high latitudes are not only one of the most sensitive regions to climate change,but also one of the regions with the most serious functional degradation of the system affected by human activities.In this context,strengthening the study of soil carbon and nitrogen mineralization and its response to grazing in Eurasian grasslands will help improve the understanding of global carbon and nitrogen cycles.In this study,five sample sites were selected from south to north along the Eastern Eurasian Steppe Transect and soil carbon and nitrogen mineralization in non-grazing and grazing grasslands at each site were studied using field sampling and indoor temperature-controlled incubation methods.The relationships between soil carbon and nitrogen mineralization and vegetation,soil and microorganisms in non-grazing and grazing grasslands were analyzed,and the influence mechanism of grazing on soil carbon and nitrogen mineralization was explored in this study,so as to systematically reveal the influence mechanism of climate change and anthropogenic activities(grazing)on grassland ecosystems and provid a basis for scientific protection,utilization and management of grasslands.The results of this study showed that:(1)Species richness index and Shannon diversity index were the main vegetation factors affecting soil carbon mineralization,and Shannon diversity index was the main vegetation factor affecting soil nitrogen mineralization in grazing plots.(2)Soil silt content,sand content,organic carbon content and total nitrogen content were the main soil physical and chemical factors affecting soil carbon mineralization.Grazing had different effects on soil carbon and nitrogen mineralization by altering soil physicochemical factors.(3)Soil microbial biomass nitrogen,catalase activity,urease activity,invertase activity,and soil microbial community composition were the main soil biological factors influencing soil carbon mineralization.Grazing changed soil microbial factors,which in turn affected soil nitrogen mineralization processes.(4)On the scale of transect,the aridity index explained the changes in soil carbon and nitrogen mineralization.Grazing had a negative effect on soil organic carbon mineralization,and the response ratio of soil organic carbon mineralization to grazing decreased as the aridity index increased.At relatively wet sites,grazing had a negative effect on soil nitrification and net nitrogen mineralization.At relatively dry sites,grazing had a weakly positive effect on soil nitrification and net nitrogen mineralization.(5)Grazing changed the interpretation percentage of soil carbon and nitrogen mineralization by vegetation factors,soil physical and chemical factors,and soil microbial factors.Grazing reduced the explanation of soil carbon mineralization by vegetation factors and soil microbial factors,making soil physical and chemical factors the main controlling factors,especially soil physical properties,which explaind nearly 90%of the variation in soil carbon mineralization in grazed plots.Grazing altered the soil bacterial taxa that influenced soil ammonification,decreased the influence of soil chemical factors(soil organic carbon content and total nitrogen content)on nitrification and net nitrogen mineralization,and increased the influence of soil physical properties(soil bulk density)and soil microbial factors(soil invertase activity)on soil nitrification and net nitrogen mineralization.In summary,the responses of soil carbon and nitrogen mineralization to grazing in Eurasian temperate steppes under different climatic conditions were different in the Eastern Eurasian Steppe Transect.The responses of soil carbon and nitrogen mineralization to grazing were the results of the combined effects of climate,vegetation,and soil factors,and grazing changed the contribution of vegetation factors,soil physical and chemical factors,and soil microbial factors to soil carbon and nitrogen mineralization.