Effects Of Human Trampling On Soil Organic Carbon Mineralization In Park Green Spaces Of Changchun City

Under the background of global warming,how to reduce carbon dioxide emissions has become an urgent problem to be solved,among which soil carbon sequestration and emission reduction has become one of the research hotspots of global climate change.As a place close to human activities,the park green spaces in the city provides a space for human recreational activities.With the human trampling,it has a certain impact on the physical and chemical properties and microbial community composition of urban green spaces soil,which not only leads to soil barrenness,but also affects soil microorganisms,soil organic carbon mineralization and temperature sensitivity.In order to explore the impact of human activities on soil organic carbon mineralization,this study took the main park green spaces soil in Changchun City,Jilin Province as the research object,and divided the park green spaces soil in Changchun City according to the degree of by different human trampling degrees（mild,moderate and severe）and different tree types（coniferous forest,broad-leaved forest and coniferous broad-leaved mixed forest）.The effects of human trampling on soil physical and chemical properties,soil organic carbon mineralization,soil temperature sensitivity and soil bacteria diversity were studied in order to provide theoretical reference for improving soil quality and reducing carbon dioxide emissions.The results showed that:（1）the physical and chemical properties of soil changed under the influence of different human trampling degrees and vegetation types.In general,the soil moisture content,total phosphorus（TP）,total nitrogen（TN）,soil organic carbon（SOC）and electrical conductivity（EC）decreased,and the soil p H and soil bulk density increased after human trampling.The change of soil organic carbon content was the most obvious,with an average decline of 23.70%.Soil p H and soil bulk density increased by 4.62%and 12.86%（p<0.05）on average at different levels of human trampling（mild,moderate and severe）,soil electrical conductivity decreased by 3.16%and 0.75%at mild and severe levels,respectively.Soil water content,total phosphorus,total nitrogen and organic carbon decreased by 21.22%,25.02%,21.9%and 29.01%on average at different degrees of human trampling（p<0.05）.Effects of human trampling on different vegetation types（coniferous forest,broad-leaved forest and mixed forest）differed typically,the soil p H and bulk density increased by 6.26%and 6.75%（p<0.05）,the soil electrical conductivity increased by 41.03%in coniferous forest,and the others decreased by 9.51%and 7.7%,respectively.The soil water content,total phosphorus,total nitrogen and organic carbon content decreased by 24.30%,14.17%,16.36%and16.05%respectively,without significant difference（p>0.05）.（2）Under the influence of human activities,soil organic carbon mineralization generally decreased,and the difference gradually increased with the intensification of human trampling.The mineralization rate of soil organic carbon in mild,moderate and severe degree of trampling decreased by 4%,3%and 17.03%at 15℃,respectively,and decreased 12.78%,21.27%and 45.56%at 25℃,respectively.The change range became larger due to the intensification of human trampling.The cumulative emissions of soil organic carbon mineralization decreased by 14.27%,19.57%and 29.26%at 15℃,respectively,and decreased 31%,26%and 46%at 25℃,respectively.It indicates that with the degree of human trampling intensified,the change range of temperature is increased.Soil organic carbon mineralization rates of different vegetation types（coniferous forest,broad-leaved forest and mixed forest）decreased by 23.58%,28.41%and 40.29%at 15℃,respectively,and decreased 19.99%,80.13%and 12.39%at 25℃,respectively.The cumulative emissions of soil organic carbon mineralization decreased by 32.27%,41.12%and 23.52%at 15℃,and decreased by 72.17%,11.04%and17.58%at 25℃.Soil organic carbon mineralization showed obvious differences among different vegetation types.（3）Under the influence of human trampling,the soil temperature sensitivity decreased as a whole.The temperature sensitivity coefficient of soil organic carbon mineralization(Q₁₀)of different human trampling degrees showed that it decreased by19.97%at the degree of severe trampling（p<0.05）,and decreased by 11.50%and 0.88%at the degree of moderate trampling and general trampling（p>0.05）,which did not reach a significant difference.The temperature sensitivity coefficient(Q₁₀)of soil organic carbon mineralization in different vegetation types showed that coniferous forest and broad-leaved forest increased significantly by 22.74%and 70.81%（p<0.05）,and mixed forest decreased significantly by 45.30%（p<0.05）.（4）The decrease of soil bacteria diversity caused by human trampling.The richness and diversity of soil microbial communities decreased by 5.31%and 7.57%（p<0.05）,respectively.