Characteristics Of Turnover And C-Fe Coupling Mechanism About Different Stability Organic Carbon In Paddy Soil

In terrestrial ecosystem soil organic carbon（SOC）was the largest carbon sink,whose stability and dynamic change were closely related to soil nutrient cycle and global climate change.The equilibrium process of desorption and adsorption between soil carbon and minerals（Eg:iron oxide）was the key to regulate the mineralization and fixation of organic carbon.This study used the ¹3C isotope tracer technique,with glucose used easily by microorganism as exogenetic carbon.Meanwhile,ferrihydrite,goethite and four kinds of C-Fe compounds were artificially prepared including adsorbed ferrihydrite（Fh-G）,absorbed goethite（Goe-G）,coprecipitated ferrihydrite（Fh*G）,coprecipitated goethite（Goe^*G）.We first payed close attention to study the effect of adding different stability organic matter on carbon mineralization and priming effect in paddy soil anaerobically.Then we discussed the interaction between the redox process of iron and organic carbon mineralization.It was expected to provide research ideas and theoretical basis for studying deeply soil carbon turnover process and how to explore the carbon stabilization mechanism of paddy soil in southern China.The main research results were as follows:（1）The addition of C-Fe complexes in different forms promoted the release of CO₂ and inhibited the release of CH₄ from soil mineralization.Among them,the effect of ferrihydrite series（Fh-G and Fh*G）was more intense than that of goethite series（Goe-G and Goe^*G）.Under the condition of different associate modes of C-Fe,adding exogenous glucose-¹3C stimulated the release of ¹3CO₂ and inhibited the release of ¹3CH₄.At the same time,it promoted releasing CO₂ and inhibited releasing CH₄ by original organic carbon mineralization in soil at different levels.In terms of priming effect of organic carbon associating with iron oxide in different ways,in the paddy field,PECO₂ of Fh-G and Fh*G had a weak positive effect compared with Fh.In other words,it relatively inhibited CO₂ mineralization and increased carbon fixation.So is the series of goethite-C complexes.Compared with Goe-G and Goe^*G,the inhibiting effect of carbon-ferrihydrite complexes on CH₄ production was more significant,a stronger negative cumulative priming effect.（2）The two-pool exponential decay model was used to fit carbon minerlization dynamic.It showed adding ¹3C-Fe complexes in different forms made allocation proportion to the rapidly mineralized pool of glucose-C greater than that of adding glucose alone.With the effects of Goe-G and Goe^*G significant,there was no significant difference in exogenous carbon distribution and half-life between the two kinds of carbon-ferrihydrite complexes.In addition,the rapidly mineralized pool treated by Goe^*G was the largest one,with the longest half-life and average retention time,which showed the turnover rate of exogenous C was slowed down in the paddy soil.The content of ¹3SOC or ¹3C-CUE was specifically manifested as Goe^*G>Goe-G>Fh*G or Fh-G at the end of anaerobic culture stage.Therefore,the relative stability of the four C-Fe complexes was roughly that of the goethite series>ferrihydrite series.The stability relative to the combination mode was shown as Goe^*G>Goe-G;Fh-G and Fh*G had no difference in stability.（3）The effect of C-Fe coupling on carbon minerlization in paddy soil:firstly,the relation between exogenous glucose mineralization and iron reduction rate of four kinds of C-Fe compounds conformed to the Hill model.Model fitting analysis showed that Fh,Goe combined with glucose in different ways can change the process of exogenous glucose mineralization under iron redox.Goe-G was more likely to reach the maximum of glucose mineralization rate under the condition of low iron reduction rate.Secondly,the linear fitting analysis of cumulative priming effect and iron reduction rate showed that the release mechanisms of CO₂ and CH₄ in the coupling process of soil carbon and iron in the paddy were different.The degree of effect was related to which ways of Fh,Goe associate together with glucose.Compared with Goe-G and Goe^*G,adding Fh-G and Fh*G had a more significant effect on promoting or inhibiting the carbon mineralization process.Thirdly,redundancy analysis and multiple stepwise regression analysis showed that DOC in soil and DOC in soil aqueous solution（WDOC）had more explanatory significance for exogenous glucose mineralization.Iron redox and pH were key indicators of soil endogenous organic carbon mineralization.Soil Olsen-P had an important impact on soil carbon turnover under the condition of adding different C-Fe complexes.According to the structural equation model,it was speculated that under the condition of adding exogenous C-Fe complexes,microorganisms may decomposed C-Fe complexes and released DOC,and then caused strong changes soil pH,thus affecting the redox process of iron and the nutrient utilization process such as Olsen-P.Specifically,soil DOC,Olsen-P,pH and exogenous glucose mineralization rates all worked on priming effect significantly and directly.In conclusion,this result systematically indicated the characteristics of carbon mineralization of C-Fe complexes with different stability in paddy soil,and analyzed the effect of carbon iron coupling on carbon mineralization under anaerobic conditions.It was of great significance to reveal the stabilization mechanism of soil mineral-bound organic carbon,improve soil organic carbon content,increase soil fertility and cope with global climate change.