Distribution Characteristics And Influencing Factors Of Soil Organic Carbon In Natural Forests In The Western Tropical Rainforest Of Hainan Island

It is generally believed that global carbon emissions have increased year by year,exacerbating global warming,and causing environmental problems such as global ecosystem destruction,frequent natural disasters,and glacial ablation,which seriously threatens the survival and development of mankind.Therefore,it has become the consensus of the whole society to reduce CO₂emissions and the CO₂content in the atmosphere.As one of the most important carbon reservoirs in terrestrial ecosystems,forest soil plays an important role in absorbing CO₂in the environment.Therefore,it is of great significance to identify the"carbon sink"of different forest soils,explore the accumulation law and influencing factors of organic carbon in forest soils,determine the carbon sequestration mechanism of forest soil and manage the"carbon pool"of forest soils scientifically to alleviate global warming,which has become hot topics in current research.The central region of Hainan Island is rich in forest resources,and its soil carbon pool is of great significance for Hainan to achieve carbon peaking and carbon neutrality as soon as possible.However,the cumulative characteristics and influencing mechanism of soil organic carbon have not been clarified because of the limitation of the research area.In order to identify the effects of different forest types,soil physicochemical properties,and topographic factors on the distribution and stability of soil organic carbon in the region,to investigate the potential of soil carbon pools in tropical rainforest ecosystems to contribute to the process of"carbon neutrality"and"carbon peaking"and to provide scientific basis for the effective management of soil carbon pools in the tropical rainforest ecosystem,this paper took the three most representative mountain areas in the western part of the tropical rainforest in Hainan Island,namely Jianfeng Ridge,Bawang Ridge,and Yingge Ridge,as the research objects,and collected 198 soil samples in the field.This paper analyzed the spatial distribution characteristics of soil organic carbon and its active components in primitive and secondary forests on vertical soil columns of 0-10 cm,10-30 cm,30-50 cm.Besides,the correlation between the soil organic carbon and environment was revealed.Through the research,the main conclusions are as follows:（1）In the soil columnar section of 0-50cm in the primitive forest area,the average content of SOC in different areas was ranked as follows:Yingge Ridge>Jianfeng Ridge>Bawang Ridge.The average content of SOC in the secondary forest area was ranked as follows:Yingge Ridge>Bawang Ridge>Jianfeng Ridge.In addition,the western mountainous areas had strong spatial differences,which were moderately variable.There was a significant difference among the SOC content of soil layer A,layer B and layer C（P<0.05）.However,there was no significant difference between the SOC content of layer B and layer C（P>0.05）.And soil’s"phenopolymerization"was obvious.（2）The spatial distribution and vertical distribution characteristics of the ROC content of the original forest are consistent with the SOC content distribution in the three regions.The average value of the total soil ROC was 3.34g/kg,accounting for22.88%of TOC.The average value of the total soil ROC in secondary forests was2.53 g/kg,accounting for 18.73%of TOC.The ROC content of the soil surface was significantly different from that of the middle layer and the bottom layer（P<0.05）.There was no significant difference between the middle layer and the bottom layer of the SOC content（P>0.05）.However,There was significant difference between the middle layer and bottom layer of Yingge Ridge’s primitive forest（P<0.05）.（3）The distribution range of soil p H values in the primitive forest areas of Jianfeng Ridge,Bawang Ridge,and Yingge Ridge ranged from 4.25-5.14,4.10-6.26,and 4.13-5.40,respectively;The distribution ranges of p H values in secondary forest areas were 4.61-7.42,4.81-6.53,and 4.76-6.22,respectively;Except for the dispersion of the p H value distribution in the original forest area of Bawang Ridge,the p H value of the other mountain primitive forest areas was more concentrated than that of secondary forests.The soil in the western mountainous area of the tropical rainforest was acidic.（4）Soil organic carbon is positively correlated with silt and clay particles,and negatively correlated with sand particles.The SOC with different elevation gradients of the same soil layer of the primitive forest showed an"N"trend of"low-high-low-high",while the secondary forest showed a"V"trend of"high-low-high".Generally speaking,the SOC content of the original forest increased with the rise of altitude.The secondary forest of the SOC content was higher in the foothills and higher elevations.（5）There was a negative correlation between p H value and SOC content and ROC content in the three regions.The correlation between p H value and SOC content and ROC content was Yingge Ridge>Jianfeng Ridge>Bawang Ridge.The correlation coefficients with SOC content were R²=0.489,0.236 and 0.226,and the correlation coefficients with ROC content were 0.284,0.231 and 0.225,respectively.The correlation between p H value and SOC content and ROC content of secondary forest was in the order of Yingge Ridge>Bawang Ridge>Jianfeng Ridge.The correlation coefficients with SOC content were R²=0.552,0.531,and 0.474,and the correlation coefficients with ROC content were 0.309,0.239,0.212,respectively.