Effects Of Urbanization Levels On Methane Oxidation Capacity Of Subtropical Urban Soils

In recent years,increasing levels of urbanization have led to a shift in land use types from natural ecosystems to impervious urban land,negatively impacting terrestrial ecosystem functions such as soil methane（CH₄）sinks.Through the meta-analysis of published papers,we found that although sporadic studies have reported differences in soil CH₄ sinks between urban and suburban areas,the current understanding of the impact of urbanization level on urban soil CH₄ sinks and their microbial processes is not fully understood.Studies have shown that soil methane oxidation potential can be used to characterize soil CH₄ sinks,and soil CH₄ oxidation is mainly a microbial process mediated by a specific class of soil functional microorganisms,methanotroph.Based on this,134 sample sites were selected in Shanghai,the urbanization level of each sample site was quantified and divided into three grades:low,medium and high,and the land use type of each sample site was classified.The soil methane oxidation potential was determined by collecting soil samples,the soil physicochemical properties such as soil methanotroph nutrients were analyzed,and the changes of soil methanotroph were further analyzed by real-time quantitative PCR（q PCR）technology,and the contribution rate of urbanization level to the influence of soil methane oxidation capacity was quantified by structural equation model.The main results are as follows:（1）The level of urbanization significantly affects the CH₄ oxidation capacity of urban soils.Specifically,high urbanization significantly reduced the methane oxidation capacity of urban soils compared to low and moderate urbanization levels.At the same time,there were significant differences in soil CH₄ oxidation capacity between different land use types.（2）The level of urbanization has a significant effect on soil methanotroph nutrients（total soil nitrogen,NO₃^--N and NH₄⁺-N）.As urbanization increases,total soil nitrogen levels decrease significantly.There are significant differences in total soil nitrogen content between different land use types.At the same time,with the increase of urbanization level,soil NO₃^--N content decreased significantly,and there was no significant impact on soil NH₄⁺-N content.There were significant differences in soil NO₃^--N and NH₄⁺-N content between different land use types.In general,with the increase of urbanization level,the nutrients of urban soil methanotroph decreased,and the CH₄ oxidation capacity of urban soil also decreased.（3）The results of qPCR analysis showed that the high urbanization level significantly increased the number of soil methanotroph compared with the low and moderate urbanization levels.The results of the structural equation model show that the CH₄oxidation capacity of urban soil is mainly affected by the level of urbanization and the nutrients of methanotroph.In addition,the CH₄ oxidation capacity of soil did not change with the change of soil methanotroph at different levels of urbanization.In summary,the results of this paper show that the methane oxidation capacity of urban soil decreases significantly with the increase of urbanization level.The influencing factors of CH₄ oxidation capacity of urban soil were mainly urbanization level and methanotroph nutrients,while the abundance of methanotroph did not significantly affect the CH₄ oxidation capacity of urban soil.Our results highlight the importance of urbanization level on the CH₄ oxidation capacity of subtropical urban soils,and provide a theoretical basis for the estimation of urban soil CH₄ sinks under future urbanization conditions,which has important practical and scientific significance.