Soil Carbon Sequestration Characteristics Of Oak Forests And Influencing Factors In Shaanxi Province

Based on the spatio-temporal substitution method, and took oak forests with differentstage from different areas in Shaanxi province as the research object—Shaanbei mainly forQuercus liaotungensis and Quercus acutissima，Guanzhong mainly for Quercus variabilis，Quercus acuteserrata and Quercus liaotungensis, and Shaannan mainly for Quercus variabilisand Quercus acutissima，We analyzed soil organic carbon storstage of oak forests in differentareas of Shaanxi province, and influencing factors. The main research contents mainly fromtwo aspects. The one was to contrast and analyze the soil organic carbon storstage of oakforests in different areas; the other one was to analyze from the factors which influencing soilorganic carbon sequestration. The main conclusions showed as following:（1） Soil organic carbon change tendency with the increase of oak forests stage were notconsistent in different areas. Soil organic carbon content tendency in Shaanbei areas with theincrease of oak forests stage present as increases first, then decreased, in the younge forests,the value was11.01g·kg^-1, and near-mature forests had the highest value of13.24g·kg^-1, andthe lowesr value was in over-mature forests which was10.50g·kg^-1. The highesr value ofSoil organic carbon content in Guanzhong areas appeared in the young forests which was13.98g·kg^-1, and in the middle forests the content of organic carbon decresed, after thisststage increased. In Shaannan areas, the soil organic carbon change tendency was reducing.Soil organic carbon content change trend equation in different areas were expressed as y=-0.595x²+3.5688x+7.7618，R²=0.8797；y=0.4282x²-2.7948x+15.806，R²=0.4688；y=-0.31x²+1.474x+8.824，R²=0.4044. Soil organic carbon content of oak forests inGuanzhong areas was higher than the other areas, and the value was12.13g·kg^-1, and soilorganic carbon content in Shaanbei and Shaannan areas were11.92g·kg^-1and9.83g·kg^-1.（2） Soil organic carbon storstage of different oak forest stages in different areas wereshowed as following: in shanbei areas, soil organic carbon storstage of the young forests,middle-staged forests, near-mature forests and mature forests and over-mature forests were86.66t hm^-2、83.11t hm^-2、106.75t hm^-2、97.86t hm^-2、77.22t hm^-2and in Guanzhong areas were135.08t hm^-2、82.80t hm^-2、92.79t hm^-2、108.00t hm^-2、107.51t hm^-2, and in Shaannanareas were103.84t hm^-2、71.46t hm^-2、84.86t hm^-2、105.47t hm^-2、68.85t hm^-2. The changeof soil organic carbon storstage in different areas had the same rules with the soil organiccarbon content. Soil organic carbon storstage of oak forest in different areas respectively is: inShannbei areas was90.32t hm^-2, Guanzhong areas was105.24t hm^-2, in Shaannan areaswas86.90t hm^-2.（3） Soil total nitrogen content and total phosphorus content of oak forests in differentareas had the same change trend with soil organic carbon content. The highest values were allin Guanzhong areas, second in Shaanbei areas, and Shaannan areas were the lowest. Soil totalnitrogen content in Guanzhong areas was1.12g·kg^-1, Shaanbei areas was1.03g·kg^-1and inShaannan areas was0.86g·kg^-1. Soil total phosphorus content in Guanzhong areas was1.12g·kg^-1, Shaanbei areas was1.03g·kg^-1and in Shaannan areas was0.86g·kg^-1.（4） Correlation analysis showed that soil organic carbon was significantly correlated withsoil total nitrogen, but there was no correlation between soil organic carbon and soil totalphosphorus contents, whenever in different areas or in Shaanxi province. The results showedthat increasing the soil total nitrogen will be beneficial to soil organic carbon fixed.（5） The change rules of litter biomass in different areas with the forest stage increasingwere not consistent in Shaanxi province. Shaanbei areas and Guanzhong areas had theopposite rules, litter biomass increased first and then reduced in Shaanbei areas, and inGuanzhong areas litter biomass reduced first and then increased. In Shaannan areas litterbiomass performance for half a parabolic increase with forest stage increased. Correlationanalysis showed that soil organic carbon was correlated with litter biomass in different areas.（6） With the increase of forest stage, change rules of the root biomass of0^-20cm and20-40cm were same, and the change law presented the tend of increase-decrease-increase inShaanxi province. The averstage root biomass of the young forests, middle-staged forests,near-mature forests and mature forests and over-mature forests in the layer of0-40cm inShaanbei areas were0.84kg·m^-2、0.97kg·m^-2、0.71kg·m^-2、0.65kg·m^-2、0.87kg·m^-2,and inGuanzhong areas were0.25kg·m^-2、0.27kg·m^-2、0.35kg·m^-2、0.24kg·m^-2、0.27kg·m^-2, and inShaannan areas were0.23kg·m^-2、0.35kg·m^-2、0.28kg·m^-2、0.21kg·m^-2、0.24kg·m^-2. In Shaanbeiareas, Guanzhong areas and Shaannan areas, root biomass of0^-20cm can separatelyaccounted for0-40cm total root biomass of61.7%-71.1%,59.6%-71.1%and61.1%-69.2%.Correlation analysis showed that soil organic carbon content of0^-20cm soil layer had noobvious relationship between root biomass of0^-20cm.（7） Canonical correspondence analysis （CCA） can simultaneously comprehensive soilfactors and environmental factors, it can analyze the different environmental factors which effect on soil organic carbon fixed. CCA analysis results show that the soil organic carbon andsoil total nitrogen have a good relationship. Different environmental factors which influencedthe soil organic carbon performance as: elevation> litter biomass> aspect> slope> rainfall>slope position. Altitude and litter biomass were the main environmental restriction factors onspatial variability of soil organic carbon, total nitrogen.