Influence Of Different Management Methods On Soil Organic Carbon In Natural Forest Of Quercus Aliena

The sharp-tooth oak（Quercus aliena var.acuteserrata）natural forest is an important forest type in the Qinling Mountains of China,with various ecological functions.Under the increasingly frequent human activities and climate change,the sharp-tooth oak natural forest has been disturbed,resulting in a decline in ecological benefits and a significant decrease in average carbon density.Scientific management methods are urgently needed to harness its carbon sequestration potential and respond to the national“carbon neutrality”policy.Therefore,this study focuses on the sharp-toothed oak natural forest.Using a comparison experiment established in 2013 in Plot 3 of Daganzigou in Baihualin Forest Farm,Xiaolongshan,the study compares the three management models:unmanaged control（UC）compared with Close-to-natural forest management（CNFM）,Structure-based forest management（SBFM）and Secondary forest comprehensive silvicuture（SFCS）.The study aims to investigate the impact of these management models on soil carbon storage and their influencing factors.The main research contents include:（1）the effects of the 3 management methods on soil organic carbon（SOC）and its active components in each soil layer of 0-30cm,including microbial biomass carbon（MBC）;（2）the effects of the 3 management methods on four environmental factors of physical,chemical,enzymatic activity,and understory biological characteristics in the topsoil of 0-10 cm;（3）exploring the coupling relationship between environmental factors and SOC and its components to further clarify the regulatory mechanisms affecting organic carbon changes.The research results can provide a theoretical basis for further expanding and improving the research technology system of the relationship between management modes and ecological functions,and provide a theoretical basis for secondary forest management in China.The main conclusions of this study are as follows:1.Among the 3 management methods,SBFM has a significant effect on the accumulation of SOC,especially in the 10-30cm soil layer,where the accumulation effect is more significant.The content of active SOC components in SBFM is closest to that of UC,and the content of ROC is significantly lower,which reflects the good carbon sequestration ability and stability of SBFM.The accumulation effect of CNFM on SOC is not significant,and its soil DOC content is significantly lower,indicating that the limited forest litter in CNFM restricts its carbon sink capacity.The difference in SOC and its component content between SFCS and UC is significant,indicating that SFCS is not conducive to the accumulation of SOC.The content of SOC components all showed a decreasing trend with increasing soil depth,and forest management did not change the vertical variation pattern.SOC,MBC,POC,LFOC were significantly enriched in the soil surface,which is in line with the characteristics of decomposition and transformation of SOC and its components in the soil.The vertical variation of soil DOC and ROC is gentle,indicating that the infiltration of water has increased the input of carbon in deep soil.2.There are significant differences in soil environmental factors and understory biological characteristics among different forest managementmethods.In terms of soil physical properties,all 3 management methods increased soil BD and decreased soil TSP.Compared to UC,the CNFM had significantly higher soil BD,while the SBFM had significantly higher soil TSP,indicating that the latter two management modes were more likely to cause soil compaction.In terms of soil chemical properties,management led to a decrease in soil p H,resulting in soil acidity.Soil TN and TP content in SBFM was significantly higher than that in CNFM and SFCS,indicating that SBFM is conducive to nutrient accumulation in soil.Management also led to a decrease in soil Ca²⁺,indicating that measures such as logging taken during management reduced the interception effect of the forest canopy,thereby intensifying leaching in the forest and leading to soil acidification.In terms of enzyme activity,soilβ-G and LAP in SBFM were significantly lower,indicating that the soil had sufficient available nutrients,and the competition for soil microbial nutrients weakened.In terms of understory biological characteristics,the diversity of shrubs and grasses increased in CNFM and SBFM after management,indicating that the quality and stability of the forest stand increased.The SB and HB was higher in SBFM,indicating that the plants in the forest had formed a multi-level pattern of nutrient utilization.The HB and FRB in SFCS were high,while the SB was low,indicating that herbaceous plants were distributed throughout the forest,and the quality of the forest was not high.3.There is a significant correlation between SOC and its components and environmental factors.Among soil physical factors,SOC is positively correlated with SWC and negatively correlated with soil TSP.Among soil chemical factors,SOC is significantly positively correlated with soil TN,TP,NO₃^-,AP,and Mg₂⁺,and negatively correlated with soil NH₄⁺.Among soil enzyme activities,SOC is highly positively correlated with soilβ-G,β-X,CBH,and NAG,and highly negatively correlated with soil AKP.Among the diversity of shrubs and grasses,all diversity indices were negatively correlated with SOC.Among understory biological factors,there was a highly significant positive correlation between SOC and LBL,LBB,and FRB.Redundancy analysis showed that environmental factors drive changes in SOC and its component content,with the cumulative explanatory power in RDA1 and RDA2 from high to low being:chemical factors（83.57%）>understory shrub and grass diversity（76.93%）>enzyme activity（55.90%）>physical factors（41.65%）>understory biological factor biomass（39.21%）.It can be seen that chemical factors,understory shrub and grass diversity,and enzyme activity have a greater impact on changes in SOC and its components,among which SWC,NO₃^-,NH₄⁺,Mg²⁺,β-G,and FRB are key environmental factors driving changes in SOC.