The Regulations Of Soil Carbon On Small-scale Spatial Variation Of Methane Oxidation Activity In Altingia Grlilipes Forest

In recent years,with the rapid increase in the concentration of greenhouse gases,the reduction of greenhouse gas emissions has become a problem that every country must face.As the second largest greenhouse gas,methane has a global warming potential 84times that of carbon dioxide on a 20-year scale(IPCC Fifth Assessment Report).Therefore,in the context of global warming,the sources of greenhouse gases,emission reduction strategies,and the factors affecting their dynamic changes have become not only ecological issues,but also global political and economic issues.The Paris Agreement proposes to"strive to achieve carbon neutrality by 2060",to achieve the goal of zero greenhouse gas emissions,and reducing methane emissions is the most direct and effective way to slow down global warming in the short term.The subtropical zone is a sensitive zone for global change.Research on the influence of soil carbon on the absorption of methane in subtropical evergreen broad-leaved forests has important practical significance for the rational use of evergreen broad-leaved forests and the response to regional climate change.In this study,the spatial variability of low concentration methane oxidation activity in forest soil was investigated at three small scales of soil depth,slope position and different distances from the tree trunk,and the effects of soil carbon source material and carbon fraction on the spatial distribution of methane oxidation activity were also explored in Altingia grlilipes forest.The results showed that:The rate of methane oxidation in Altingia grlilipes forest soils ranged from 0.0132 to0.0686?g·kg^-1·d^-1 with a mean value of 0.0442?g·kg^-1·d^-1.The ANOVA results showed that soil depth,distance from the trunk and slope position had significant effects(P<0.05)on the methane oxidation activity of soil in Altingia grlilipes forest.In the range of 0?15cm soil layer,the highest mean methane oxidation rate was found in the subsurface layer of 3?6 cm soil,reaching 0.0464?g·kg^-1·d^-1.The lowest value was found in the 0?3 cm soil layer,and the methane oxidation rate gradually decreased in the 6?15 cm.The mean values of soil methane oxidation activity were upper slope(0.0477?g·kg^-1·d^-1)>middle slope(0.0475?g·kg^-1·d^-1)>lower slope(0.0373?g·kg^-1·d^-1),showing a gradual decrease from upper to lower slope.The maximum methane oxidation activity was 0.0473?g·kg^-1·d^-1 at a horizontal distance of 3.0 m from the tree trunk.These results suggest that there is a large spatial variability in forest soil methane oxidation activity at three small scales:soil layer,slope position and distance from the tree trunk.Correlation analysis showed that methane oxidation activity showed a significant negative correlation with total carbon and total nitrogen at a confidence level of 0.01,with correlation coefficients of-0.298 and-0.256,respectively.There was no significant correlation between methane oxidation activity and carbon to nitrogen ratio,bulk weight,DOC,and glucose content.Methane oxidation activity showed a significant positive correlation with mucilage at a confidence level of 0.01 with a correlation coefficient of0.268.The absence of correlation between methane oxidation activity and soil aeration factors(moisture,soil water content,and bulk weight)and the negative correlation with clay content in this study indicate that the methane oxidation activity measured by the"bulk soil indoor culture method"excludes the influence of gas diffusion factors on methane oxidation activity and represents the size of the methanogenic population.Based on the results of correlation analysis between soil VOCs(volatile organic compounds)emissions and methane oxidation activity,the main carbon substances affecting the methane oxidation activity of this forest soil were screened to be methanol and acetic acid.In the exogenous carbon addition experiment,methanol,formic acid,acetic acid,glucose,cellulose,humic acid and monoterpenes were added to the soil at different concentrations to further analyze and identify the carbon substances that have a regulatory effect on the methane oxidation activity of forest soil.The results showed that both high and low concentrations of humic acid,cellulose and glucose additions did not have immediate and delayed inhibition of methane oxidation activity.The addition of?-pinene and?-pinene at high and low concentrations also did not have immediate and delayed inhibitory effects on methane oxidation activity.Low concentrations of methanol addition(81.7 nmol·g_dw^-1)were able to produce an immediate inhibition of methane oxidation activity,and this inhibition lifted after one month of addition.Formic acid addition inhibited methane oxidation activity only at very high concentration addition levels(>4083.7 nmol·g_dw^-1,well above the natural formic acid content of forest soils).Methane oxidation activity was inhibited by75%when the acetic acid addition reached>816.7 nmol·g_dw^-1,at which point the acetic acid addition was close to the upper limit of natural acetic acid content of the forest soil.Based on these results,it can be seen that the in vitro culture method can eliminate the influence of physical diffusion factors on methane oxidation activity.Although the methane oxidation activity is affected by many carbon substances,only methanol and acetic acid can affect the methane oxidation activity at the field concentration level.Therefore,it is necessary to conduct a systematic and depth study on the regulation effects of acetic acid and methanol on the oxidation of methane in forest soils in the future.