| With the deepening understanding of the importance of land use change,the impact of land use change on soil carbon and nitrogen gradually became the focus of scientific research workers.Soil microbe,as an important component of soil organic carbon,is also a key parameter to measure soil nutrient cycling.The change of land use pattern will change soil microbial composition and community structure by affecting soil carbon and nitrogen balance.Therefore,a systematic study of soil carbon,nitrogen and microbial community structure under different land use patterns can predict the impact of different land use patterns on land productivity and soil health,which having great significance in theory and practice.In this study,With rice paddy field as a control,the Metasequoia glyptostroboides(MQ)forests(16-year-old,25-year-old,35-year-old),20-year-old Cinnamomum camphora(CC)forest and deforested land(used to be 25-year-old Cryptomeria Fortunei forest)were investigated at Dongping National Forest Park in Chongming island.The soil organic carbon,total nitrogen and microbial biomass carbon,microbial biomass nitrogen,mineral nitrogen and nitrogen mineralization rate were analyzed by using three plots of land use types,the method of PLFA were used to study the spatial differentiation of microbial community structure under different land use patterns.The differences of soil carbon,nitrogen and microbial community structure in different land use patterns and soil layers in Chongming Island were analyzed by combining their physical and chemical properties and enzyme activities.The mechanism of various factors in soil C and N was also analyzed.The main conclusions are as follows:1)Compared with the paddy field,the pH value of the soil decreased,and the 2-0.25 mm water-stable macroaggregates increased,the Macro-aggregates showed a tendency to transform to Micro-aggregats.And the improvement effect was enhanced with the growth of forest age,while the deforestation was not conducive to the improvement of physical and chemical properties.There were also differences in soil physical and chemical properties between different vegetation types and different planting years.2)In the process of returning farmland to forest,the content of soil carbon and nitrogen was decreasing in the short term,but in the long-term,the soil organic carbon and nitrogen storage capacity in the soil was higher than that in the paddy field.And The ability to maintain microbial biomass carbon,microbial biomass nitrogen,ammonium nitrogen and nitrate nitrogen was also better,while deforestation reduced soil nitrogen mineralization by affecting soil physical and chemical properties so as to reduce the content of organic carbon and nitrogen in the soil.Tree species and age are also the important factors that affect soil organic carbon and nitrogen content and distribution.3)In the soil enzyme activity,the transformation of paddy field to forest land could further increase soil enzyme activity,while deforestation would reduce it.The tree species and age were also important factors affecting soil enzyme activities in different tree species.And the pearson correlation analysis showed that there were significant or very significant positive correlations among the four soil enzyme activities.4)Different land use types had significant effects on microbial community structure(p < 0.05),the tree species and age are the important factors affecting the structure of significant microbial community.5)Correlation analysis showed that the soil physical and chemical properties,soil carbon,nitrogen and their components,enzyme activity,microbial community structure have mutual influence through a certain coupling mechanism.The main features of this study are the analysis of the key factors that cause different organic matter content in different land use patterns,Revealing the mechanism of soil organic matter change,And provide some scientific basis for the sustainable development and ecological benefit evaluation of land use pattern in Chongming Island. |
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