| Deep soil(>30 cm)is a key component of the terrestrial carbon cycle.More than 77%of the organic carbon is stored in the deep soil,revealing that the stability of the deep soil organic carbon is crucial to the quantitative assessment of the global soil carbon cycle.Biochar has the characteristics of rich carbon contenthigh stability,and the effect of reducing soil greenhouse gas emissions.Its application to soil is considered to be an important way for soil carbon sequestration.Fundamentally,the biochar reported by a large number of existing literature has a significant effect on the dynamics of soil organic carbon on surface,and at the same time,the effect of biochar on the stability of deep soil organic carbon is rarely reported.Therefore,in order to accurately assess the soil carbon sequestration of biochar at a larger spatial scale,it is particularly important to analyze the distribution dynamics and stability changes of soil organic carbon at different depths under the application of biochar.In this study,paddy soils in southern China were treated with corn straw biochar(15 t·ha-1)for 2 years Two treatments were set in the field experiment:biochar treatment and no biochar treatment(control).The biochar used in the experiment was pyrolyzed from corn straw at 450℃ with an application rate of 15 t·ha-1.In order to study the effect of a single biochar on the dynamics of deep soil organic carbon,soil samples with a depth of 0-80 cm were collected after 2 years of biochar application,and the content of soil organic carbon components at different depths was analyzed,investigated the organic carbon components and organic carbon mineralization characteristics from deep the paddy soil.Moreover,this study investigated the sensitivity of soil organic carbon mineralization to temperature and nitrogen addition at different depths under biochar application.The results classified the effect of short-term biochar application on deep soil organic carbon stability.The main findings are as follows:1.The application of biochar significantly increased the surface organic carbon content of the soil on the two-year scale,and significantly changed the content of deeplayer(0-40 cm)soil active organic carbon and its distribution characteristics in total organic carbon.Compared with the control,biochar application significantly increased the surface organic carbon content(0-10 cm)by 15.8%,but had no significant effect on the total organic carbon content of deep soil.Compared with the control treatment,the content of labile organic carbon in the soil treated with biochar was significantly reduced at 0-40 cm soil depth,with 9.8%,20.2%,44.2%,and 44.9%in the layer of 010 cm,10-20 cm,20-30 cm,30-40 cm,respectively.Except for the surface layer(0-10 cm)with an significant increase of 11.3%,the microbial biomass carbon decreased significantly by 14.9%,50.1%,and 45.0%in 10-20 cm,20-30 cm,and 30-40 cm soil layers.At the same time,the application of biochar significantly increased the dissolved organic carbon content in the soil depth of 0-40 cm,and the increase in the four soil layers of 0-10 cm,10-20 cm,20-30 cm,30-40 cm reached 61.3%,68.6%,79.9%and 49.3%respectively.However,in 40-80 cm soil,the content of each active organic carbon component was not significantly different between the two treatments.At the same time,this study found that biochar application also had a significant effect on the distribution characteristics of soil active organic carbon components.Compared with the control treatment,the biochar treatment significantly reduced the portion of labile organic carbon and microbial biomass carbon in soil organic carbon at 0-40 cm depth,with a decrease by 22%,15%,33%,26%and 7.3%,15.2%,49.1%,47.6%at 0-10 cm,10-20 cm,20-30 cm,30-40 cm soil layer,respectively.Meanwhile,the distribution ratio of dissolved organic carbon in the soil organic carbon of each soil layer of 0-10 cm,1020 cm,20-30 cm,and 30-40 cm increased significantly,with increases of 38.6%,75.2%,78.7%,and 50.7%respectively;at 40-80 cm depth,biochar application did not change the distribution characteristics of soil active organic carbon components.2.The effect of biochar application on the organic carbon mineralization of deep soil varied with the depth of the soil layer.Compared with the control,the application of biochar significantly reduced the mineralization intensity of organic carbon in the soil layer of 0-40 cm,and the reduction rates in the four soil layers of 0-10 cm,10-20 cm,20-30 cm and 30-40 cm were 23.74%,37.57%,37.63%and 15.96%respectively,and reduced the microbial metabolic entropy of the corresponding soil layer,while in the 40-80cm soil layer,both have no significant changes.3.The application of biochar significantly reduces the sensitivity of the surface(010 cm)soil organic carbon decomposition to temperature,and has no significant effect on the deep layer.Compared with the control,the Q10 of the surface soil(0-10 cm)treated with biochar was significantly reduced by 11.32%,but had no significant effect on the soil below 20 cm.At the same time,in the range of 15℃～35℃,the mineralization rate and mineralization rate of soil organic carbon at all layers increase with the increase of temperature.4.The application of biochar reduces the nitrogen supply in the soil profile,and the response of deep soil organic carbon mineralization to nitrogen addition is significantly greater than that in the surface layer.Compared with the control,biochar application significantly reduced the soil inorganic nitrogen content of 0-40 cm,which may limit the activity of microorganisms at the corresponding level,and then have a certain impact on the organic carbon mineralization.In addition,with the increase of nitrogen levels,the mineralization intensity of organic carbon in the surface layer(0-10 cm)and deep paddy soil increased significantly,but the increase in the deep soil was significantly greater than that in the surface layer,indicating that the presence of nitrogen restrictions in the deep soil affected its organic carbon mineralization.In summary,the application of biochar to the surface of the paddy field continuously affected not only the content and stability of the organic carbon in the top soil on the two-year scale,but also the composition of the organic carbon pool and the intensity of mineralization of organic carbon in deep soil(below 20 cm).However,There was no significant change in the temperature sensitivity of organic carbon mineralization in deep soil.Although the response of deep soil organic carbon mineralization to nutrient input(addition of nitrogen)is significantly higher than that of the surface layer,the application of biochar has no significant effect on it,and the long-term impact of biochar on the dynamics of deep soil organic carbon in paddy fields still needs further the study. |
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