| Guizhou Province is located in the center of karst landforms in southwest China,and is one of the most typical provinces with karst landforms in China.Due to the unique geological background,complex interlaced land use types and long-term human disturbance in Guizhou Province,the soil organic carbon(SOC)in this area has a high degree of spatial heterogeneity,which also brings great difficulties to the estimation of SOC storage and the study of controlling factors.Currently,research on the spatial variability and controlling factors of SOC in Guizhou Province is mainly focused on small watersheds or scales,while research on larger spatial scales(such as provincial scales)is rarely reported.Therefore,based on 510 soil samples collected in Guizhou Province,this study analyzed the spatial variability of SOC content and density in Guizhou Province,and explored the relationship between SOC content,density and influencing factors.The SOC storage of typical land use types in Guizhou Province was estimated.By constructing a model,identify the main controlling factors that affect the spatial variation of SOC and evaluate the impact pathways and mechanisms of each factor on SOC.The research on the above contents provides a theoretical basis for in-depth understanding of the regional carbon cycle,formulating and implementing the regional carbon sink strategy and achieving the"double carbon"goal.The main conclusions are as follows:(1)The SOC content and density of the two soil layers(0～10 cm and 10～20 cm)in Guizhou Province showed moderate intensity variation.The results of semivariogram model showed that the SOC content and density of grassland in two soil layers had strong spatial autocorrelation.the SOC content and density of cultivated land in two soil layers had moderate spatial autocorrelation.The SOC content and density of forest land in 0～10 cm soil layer had strong spatial autocorrelation,while the forest land in 10～20 cm soil layer had moderate spatial autocorrelation.There was no spatial autocorrelation of SOC density in the garden land.The results of Kriging interpolation showed that the high SOC content and density values were mainly concentrated in the west of Guizhou Province,while the low SOC content and density values were mainly concentrated in the south and north of Guizhou Province,but there were certain differences among various land use types.(2)The SOC storage of forest land in Guizhou Province was288.65×10~6t(0～10 cm)and 476.47×10~6t(0～20 cm),respectively.The SOC storage of cultivated land was 73.69×10~6t(0～10 cm)and 139.8×10~6t(0–20 cm),respectively.The SOC storage of garden land was 12.04×10~6t(0～10 cm)and 22.53×10~6t(0～20 cm),respectively.The SOC storage of grassland was 4.42×10~6t(0～10 cm)and 7.66×10~6t(0～20 cm),respectively.(3)Under different altitude gradients,the SOC content and density in Guizhou Province increased with altitude.At different slope positions,the SOC content and density at downhill and mountaintop were relatively high,and the SOC content and SOC density at the flat ground/toe of slope and mesoslope were relatively low.In different slope aspects,the SOC content and density of semi-sunny slope and sunny slope were relatively higher than those of semi-shady slope and shady slope.Under different slope gradients,the high values of SOC content and density mainly appeared in the area of slope>35°and 6°～15°.Under different land use types,the SOC content and density of woodland were the highest in 0～10cm soil layer,and the SOC content and density of paddy field were the highest in 10～20 cm soil layer.In different soil types,SOC content and density of limestone soil were relatively higher than those of yellow soil and paddy soil.Under different temperature gradients,SOC content and density decreased with the increase of temperature.Under different precipitation gradients,SOC content and density were relatively high in areas with precipitation of 800～1200 mm,and relatively low in areas with precipitation of 1600～2100 mm.SOC content and density were significantly positively correlated with soil moisture content,total phosphorus,total nitrogen,copper,iron and zinc(P<0.01),and significantly negatively correlated with potassium(P<0.01).(4)The results of structural equation model(total effect)and random forest model(importance ranking)showed that soil moisture content,altitude and total phosphorus were the key control factors affecting SOC variation.Human disturbance and light intensity only had direct effects on SOC content and density in 0～10 cm soil layer.Soil moisture content had the strongest direct effect on SOC content and density in two soil layers.The indirect effect of altitude on SOC content in the 0～10 cm soil layer and SOC density in two soil layers was the largest,and the indirect effect of precipitation on SOC content in the 10～20 cm soil layer was the largest.Slope position and slope indirectly affect SOC by negatively affecting human disturbance,and precipitation indirectly affects SOC by positively affecting human disturbance. |
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