| Glacier melting and biological extinction caused by global warming will bring huge impact on society and natural ecosystems.Improving soil carbon sequestration capacity is one of the measures to slove global warming.Robinia pseudoacacia is the main afforestation tree in the loess hilly and gully area,understanding its soil carbon sequestration capacity can improve the scientific basis for the estimation of carbon storage in the region.By taking the Robinia pseudoacacia-Platycladus orientalis(RP)mixed forest with different ages(RP1: 7 a;RP2: 13 a;RP3: 23 a)as research objects,and taking Robinia pseudoacacia(R)pure forest with different ages(R1: 7 a;R2: 13 a;R3: 23 a)as control in Yongshou County,we analyzed soill physi-chemical properties,enzyme activity,soil organic carbon(SOC)and soluble organic carbon(DOC)?easily oxidizable organic carbon(EOC)and microbial biomass carbon(MBC)at the 0 ? 60 cm soil layer,aimed to reveal the difference and influencing factors of soil carbon sequestration capacity between mixed forest and pure forest The primary results were as follows:(1)The soil physi-chemical properties and enzyme activity of the two forest types changed regularly with the increase of forest age.At each soil layer,the soil bulk density of mixed forest increased firstly,and then decreased,and the soil bulk density of pure forest promoted with the increase of the forest age.The soil clay content of mixed forests promoted with the increase of forest age,while the silt content was opposite,and there was no obvious change in pure forest.The total phosphorus content of mixed forest promoted firstly,and then decreased,while pure forest continued to increase.The soil capillary porosity,total porosity,sand content,total nitrogen content,sucrase,amylase,and catalase activities of the two forest types promoted with the increase of forest age,while the soil p H was opposite.The soil non-capillary porosity,cellulase activity had no obvious change.(2)There were obvious differences in the physi-chemical properties and enzyme activities of the two forest types.Compared with the pure forest,the soil physi-chemical properties and enzyme activities did not improve significantly at the initial stage of the mixed forest,but with the increase of the forest age,its improvement effect became more and more significant.The soil bulk density of RP3 mixed forest increased-5.03% ?-6.67%in each soil layer,and the soil capillary porosity,non-capillary porosity and total porosity of RP3 mixed forest increased significantly by 1.69% ? 8.75%,17.86% ? 40.82% and 3.62%.?8.59%,the soil clay content of mixed forests at each forest age stage increased by0.24%-20.10%,and the sand content and silt content of RP3 mixed forests increased-0.94%?-5.44% and 1.37% ? 10.31%.The total nitrogen content,total phosphorus content and p H of the RP3 mixed forest in each soil layer significantly increased by 6.20% ? 25.04%,-17.45%? 23.51% and-0.24% ?-1.10%;the RP3 mixed forest had a significant increase in soil invertase in each soil layer.Amylase,cellulase and catalase activities significantly increased by 40.72% ? 112.14%,4.21% ? 26.42%,31.23% ? 49.69% and 7.01% ? 34.98%.It showed that mixed forest could improve soil physi-chemical properties and increase soil enzyme activity.(3)The content of SOC and active organic carbon of the two forest types changed regularly with forest age.The content of SOC and active organic carbon in the mixed forest and pure forest promoted with the increase of forest age,but the distribution ratio of soil active organic carbon did not change significantly with forest age.(4)There were significant differences in soil organic carbon and active organic carbon content between the two forest types.Compared with the pure forest,the SOC and active organic carbon content of mixed forest promoted in the early stage of mixing,but there was no significant difference.As the forest age increased,the soil carbon sequestration capacity was significantly improved.Compared with pure forest,the soil SOC content of RP2 and RP3 mixed forest increased significantly by 25.54% ? 38.69% in each soil layer,and the soil EOC,DOC and MBC content of RP3 mixed forest significantly increased by 16.33% ?30.12%,43.57% ? 70.49% and 21.35 % ? 25.29%,indicating that the SOC accumulation characteristics of RP3 mixed forest were obvious.(5)There were obvious differences in the distribution ratio of soil active organic carbon between the two forest types.Compared with the pure forest,the DOC/SOC and MBC/SOC of the mixed forest had significant differences at the RP3 stage,which significantly promoted-7.34% ?-40.41% and-2.41% ?-13.40 at the three soil layers.There was a significant difference in soil EOC/SOC at the RP2 and RP3 stages,and it promoted significantly at the three soil layers by-6.11% ?-26.01%.The soil SOC of the mixed forest was more stable and more conducive to the accumulation of SOC(6)Soil physi-chemical properties and enzyme activity had significant effects on soil organic carbon and active organic carbon content.Soil sucrose,amylase activity,clay content,total nitrogen content,and capillary porosity were the important factors affecting SOC and active organic carbon in the two forest types,and the cumulative interpretation of relationship was over 97%.In addition,the driving factor for the difference in the content of SOC and active organic carbon between the two forest types was soil enzyme activity.The mixed forest had the greatest impact on organic carbon and active organic carbon by amylase activity,while the pure forest was sucrase enzyme activity.In summary,the mixed forest was beneficial to improve soil physical and chemical properties,increase soil enzyme activity,promote SOC accumulation,and also help balance the distribution ratio of active organic carbon and improve SOC stability with the increase of forest age. |
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