Effects Of Different Vegetation Types On Soil Organic Carbon And Its Active Components In Karst Area

Scientific understanding of soil organic carbon pool is of great significance for understanding the structure and function of soil ecosystem and dealing with environmental problems such as climate warming.The carbon cycle in the karst area of Southwest China shows distinct characteristics different from other regions,but due to unreasonable human activities,the phenomenon of rocky desertification in the karst area is severe.Vegetation restoration has become the main measure to control rocky desertification in this area.Therefore,in this study,grassland,grass-shrub mixed forest,shrub forest,tree-shrub mixed forest and understory soil in karst area were selected as the research objects to explore the differences of soil organic carbon and its active components in content,storage and stability under different vegetation types,and to clarify the direct or indirect effects of soil and litter physical properties and soil enzyme activities on soil organic carbon pool.In order to provide theoretical basis for vegetation restoration and management in karst area.The main conclusions are as follows :(1)The soil organic carbon(SOC)content of different vegetation types in the study area ranged from 17.57 to 70.45g/kg,the easily oxidized organic carbon(EOC)content ranged from 0.90 to 9.31 g/kg,the soluble organic carbon(DOC)content ranged from 217.39 to449.92 mg/kg,the light fraction organic carbon(LFOC)content ranged from 0.23 to 7.44g/kg,and the microbial biomass carbon(MBC)content ranged from 325.77 to 2113.53 mg/kg.In general,the soil of arbor forest is higher than that of other vegetation types.The carbon efficiency of different active carbon fractions in soil showed that the DOC carbon efficiency of grassland was the highest,which was significantly higher than that of arbor forest and arbor-shrub compound forest,indicating that grassland community had a negative effect on SOC accumulation process.There was no significant difference in EOC carbon efficiency among shrub forest,arbor-shrub composite forest and arbor forest.MBC carbon efficiency was higher in arbor forest and arbor-shrub mixed forest than other vegetation types.(2)The soil physical properties of arbor forest are better than other vegetation types.The physical properties of the upper soil are better than the lower soil.The content of soil total and available nutrients in 0～10cm was significantly higher than that in 10～20cm and20～30cm soil layers,showing ’ surface aggregation ’.The contents of soil total nitrogen,available nitrogen,available phosphorus and available potassium in arbor forest and arbor-shrub composite forest were higher than those in other vegetation types.C:N in grassland was significantly higher than that in arbor forest,indicating that arbor forest community was more conducive to storing nutrients.N:P reflects that the nutrient limitation type in this study area is nitrogen limitation.The results of correlation analysis between soil physical and chemical properties and soil organic carbon and its active components showed that soil physical and chemical properties affected soil organic carbon and its active components to varying degrees.Except that soil bulk density and C:N were negatively correlated with organic carbon and its active components,other indicators showed positive correlation.The physical and chemical factors affect the soil organic carbon pool through interaction.Further redundancy analysis showed that the minimum soil water holding capacity and total nitrogen content had the highest explanation for soil organic carbon and its components.(3)The litter of arbor-shrub composite forest has a large volume,and the litter of arbor forest has better water holding capacity.The contents of organic carbon,total nitrogen,total potassium and lignin in litter changed with the increase of decomposition degree.Specifically,organic carbon,total nitrogen and lignin decreased with the increase of decomposition degree,while total potassium increased with the increase of decomposition degree.Nutrient stoichiometry showed that shrub litter had higher decomposition rate and stronger nutrient return ability.The results of redundancy analysis showed that the soil organic carbon pool under arbor forest and arbor-shrub compound forest was more significantly regulated by litter related factors.(4)The activities of alkaline phosphatase,urease and catalase were the highest in arbor forest soil and the lowest in grassland.The sucrase activity of arbor-shrub composite forest was higher than that of arbor forest.In the vertical soil profile,the soil enzyme activities were higher in the upper soil than in the lower soil.Soil enzyme activity was significantly correlated with soil organic carbon and its active components,especially urease activity.The results of redundancy analysis showed that the effects of soil enzymes on soil organic carbon pool in arbor-shrub composite forest and arbor forest were more significant than other vegetation types.(5)Overall,our results showed that soil physical and chemical properties,litter and soil enzyme activities,soil physical and chemical properties were the dominant factors affecting soil organic carbon and its active components.Compared with other vegetation types,arbor forest community has higher litter regression and primary productivity level,which can form a more stable nutrient circulation system,and the soil organic carbon pool under this community is more stable.Based on soil organic carbon pool,shrubs and trees can be selected for vegetation restoration.