Effects Of Different Forest Types On Soil Carbon Sequestration And Stability In Changsha City

The global climate change caused by the greenhouse effect has a huge impact on the natural environment that human beings depend on for survival,and various climate extremes have occurred frequently in recent years,which seriously threaten the survival of human beings.As a major source of carbon emissions,improving the carbon sequestration capacity and stability of urban soils is one of the important ways to mitigate global climate change.At present,some studies on soil organic carbon fraction and soil mineralization on soil carbon sequestration in different forest types have been reported,but few studies on soil carbon sequestration and stability in different urban forest types have been reported.In this study,we set up experimental plots in a subtropical city to determine the nutrient contents of litter,fine roots and soils,the physical and chemical properties of soils,soil organic carbon(SOC),soluble organic carbon(DOC),soluble organic carbon(DOC),easily oxidized organic carbon(ROC),microbial biomass carbon(MBC)and soil mineralization.To investigate the effects of different forest types on soil carbon fraction and carbon storage by litter,fine roots and soil physical and chemical properties,and the effects of soil factors on soil mineralization,to investigate the effects of different urban forest types on soil carbon sequestration capacity,to understand the dominant carbon sequestration species in plantation forests and to provide the scientific basis for the selection and breeding of dominant species and the cultivation of plantation forests.The main research results are as follows:(1)Soil bulk density(BD)ranged from 1.29-1.58 g·cm-3 with PMF being the largest and CCF the smallest;water content(SWC)showed the opposite pattern to BD;soil pH ranged from 4.28-4.61,all were acidic soils;organic matter(SOM),total nitrogen(TN)and total phosphorus(TP)were higher in LFF and PMF than in CCF and MIXF,with the "surface aggregation" phenomenon;MIXF reduced soil BD and increased soil pH,MIXF soil SOM,TN and TP contents were lower,and tree species mixing increased soil nutrient consumption.(2)Soil SOC content and carbon storage(SOCR)were both highest in PMF and lowest in MIXF;DOC,ROC and MBC showed different patterns of performance,with PMF soils having lower ROC and MBC content,less carbon that can be easily decomposed and fewer soil microorganisms,and more carbon that can be sequestered;microbial entropy(MBC/SOC)indicated that broadleaf forests converted more carbon for use by microorganisms than coniferous forests The carbon mass(DOC/SOC)indicates that PMF and CCF soils have a higher capacity to adsorb DOC,and the organic carbon stability index(RIC)indicates that CCF and PMF soils have higher organic carbon stability than LFF and MIXF;correlation analysis shows that there is a significant correlation between soil nutrients and carbon fractions;PMF soils have the highest carbon storage and the highest carbon sequestration capacity,CCF soils have higher carbon stability,and MIXF soils have a higher carbon sequestration capacity and MIXF soils have higher carbon stability.MIXF soils had the worst carbon sequestration capacity and carbon stability.(3)The contents of litter biomass(LB),litter carbon stock(LOCR)and fine root biomass(FRB)and fine root carbon stock(FROCR)of the four forest types were the highest in MIXF,followed by PMF and LFF,and the lowest in CCF.MIXF increased the accumulation of litter biomass and promoted plant growth while intensifying the consumption of soil nutrient content,which was not conducive to soil carbon accumulation and stability;litter organic carbon(LOC)content PMF was the highest,followed by CCF and MIXF,and LFF was the lowest;litter total nitrogen(LTN)and total phosphorus(LTP)content were both the highest in CCF and the lowest in PMF;fine root organic carbon(FROC)content was the highest in LFF and the lowest in MIXF;litter and fine roots explained 50.17%of the variation in soil carbon fraction and stock content,and the main influencing factor was FRB;PMF soil ROC,MBC content and MBC/SOC and DOC/SOC values are lower,the carbon content transformed and utilized by PMF microorganisms is lower,less active organic carbon is formed by decomposition of apoplastic matter,most of the carbon is input to the soil in stable form,and soil carbon sequestration capacity is stronger.(4)During soil organic carbon mineralization,LFF soil mineralization rate and cumulative mineralization were highest at 35℃ and 25℃ incubation temperature,and PMF was highest at 15℃ incubation temperature;soil cumulative mineralization rate PMF was lowest,and PMF soil had the strongest carbon sequestration capacity;soil temperature sensitivity(Q10 value)was highest for LFF and lowest for CCF,and CCF soil responded least to temperature changes;soil physical and chemical properties,and carbon fraction explained 86.74%of the variation in cumulative soil mineralization and Q10values,and soil carbon fraction and TN and TP were the main influencing factors.In summary,PMF has the highest carbon storage among the four urban forest types,PMF and CCF are more favorable to soil carbon sequestration than LFF and MIXF,and PMF has the strongest soil carbon sequestration capacity,CCF has the highest soil carbon stability,and MIXF has the worst soil carbon sequestration capacity and soil carbon stability.