Decomposition And Stabilization Mechanism Of Straw Organic Carbon During Iron Redox Process In Paddy Soil

Paddy soil,as one of the most important organic carbon pools in terrestrial ecosystems,has a strong carbon sequestration potential and plays an important role in mitigating global warming.Among them,the interaction between soil organic carbon and iron minerals is the key link affecting the mineralization and fixation of soil organic carbon.In this study,the ¹³C isotope tracer technique combined with laboratory simulation experiments was used to explore the mechanism of the addition of Ferrihydrite（Fh）and Biochar（BC）on straw turnover and stability in flooded paddy soil.this study systematically studied the mechanism of iron oxide and biochar addition on the mineralization,turnover and stability of straw in soil after returning to the field.It is of great significance to reveal the stabilization mechanism of common application patterns of iron minerals and biochar in the soil after straw return,to improve the potential of carbon sequestration in paddy soil,to apply biochar scientifically and to reduce global warming.The main research conclusions are as follows:（1）The addition of Fh and BC can increase the organic carbon mineralization of straw and soil to produce CO₂and CH₄.Compared with the addition of S alone,the addition of S+Fh and S+BC promoted the mineralization of 29.6%straw carbon and 55.7%soil organic carbon,respectively.The mix addition of Fh and BC increased the release of ¹³CO₂by 17.0%,and reduced the release of ¹³CH₄by46.7%.The overall mineralization rate of straw decreased by 29.7%,and the anti-decomposition ability of straw carbon in soil was enhanced.Secondly,the addition of Fh and BC increased the allocation proportion of straw carbon in the rapid conversion carbon pool,but this proportion was significantly reduced when the addition of Fh and BC was mixed.The addition of Fh prolonged the retention time of straw carbon in soil and enhanced the stability of straw carbon in soil.The addition of Fh+BC reduced the retention time of straw carbon in soil.Compared with the addition of S alone,the addition of S+Fh increased the CO₂priming effect by 60.3%,and reduced the CH₄priming effect by 4.2%,that is,promoted the mineralization of soil organic carbon by 56.1%.The PE_CO2and PE_CH4of S+Fh were decreased by 40.8%and 42.2%,respectively,with the addition of BC,which caused a strong negative priming effect.（2）Adding Fh inhibited the conversion of straw carbon to ¹³DOC and reduced the average ¹³DOC content by 54.9%;The addition of S+BC and S+Fh+BC promoted the conversion of straw carbon to ¹³DOC by 15.4%and 13.5%,respectively.Secondly,the addition of Fh and BC increased the amount of straw carbon converted to soil ¹³MBC by 0.01～1.00 times at the initial stage（3 d and 28 d）,which improved the utilization efficiency of straw carbon by microorganisms.However,at the later stage（70 d and 150 d）,it decreased by 0.38-0.51 times,and more straw carbon was released into the atmosphere in the form of CO₂,which reduced the utilization efficiency of straw carbon by microorganisms.Compared with the addition of S alone,The addition of S+Fh,S+BC and S+Fh+BC increased soil nutrients（NH₄⁺-N and Olsen-P）by increasing the activities of hydrolases（N-Ac and Phos）at the initial stage,In the later stage,with the decrease of hydrolase activity,soil nutrient content gradually decreased,and the promotion effect of Fh on hydrolase was stronger than that of BC.（3）The adsorption of Fh and BC enhanced the stability of straw carbon in the soil.The addition of Fh and BC promoted the conversion of 23.9%～39.1%of straw carbon into ¹³SOC at the initial stage（3 d and 28 d）.At the later stage（70 d and 150d）,Fh and BC promoted the iron reduction process and reduced ¹³SOC by32.7%～38.3%,which accelerated the utilization of ¹³SOC by microorganisms.Secondly,compared with the addition of S alone,the addition of S+Fh,S+BC and S+Fh+BC promoted the formation of>0.25 mm aggregates by30.4%,8.0%and 51.6%,respectively.But inhibited the formation of 0.053mm～0.25 mm and<0.053 mm aggregates.Meanwhile,the ¹³SOC content of>0.25mm aggregates and<0.053 mm aggregates decreased by 37.2%～70.2%and36.2%～48.9%,respectively.There was no significant effect on ¹³SOC content in0.053 mm～0.25 mm aggregates.In addition,the addition of Fh promoted the content of Fe-OC and enhanced the stability of straw carbon in the soil,while the addition of BC and Fh+BC showed no significant difference.The results of redundancy analysis and multiple stepwise regression analysis showed that soil nutrients（DOC,NH₄⁺-N,NO₃^--N and Olsen-P）added with Fh and BC had important explanatory significance for the mineralization of straw carbon.The results showed that soil DOC,NH₄⁺-N and NO₃^—N had a direct negative effect on straw carbon mineralization,while Olsen-P had a positive effect on straw carbon mineralization.