Regulations Of Soil Organic Matter Turnover By Main Clay Mineral Types Of Mollisol And Soil Texture Manipulation After Straw Addition On Mollisols

Soil organic matter（SOM）is the largest carbon pool in the terrestrial ecosystem and its size is generally determined by the balance between the organic inputs from plant production and the outputs mainly through decomposition.As plant litters are its main sources,increasing SOM through continuous inputs of crop straw into soils is the main method for ensuring farmland soil quality,food security and climate management.SOM forms when decomposition products of crop straw are intimately associated with soil minerals.Yet,mechanical understanding of mineral-organic association and its chemical composition is still lacking,and no SOM models can adequately predict mineral-organic associated strength by soil mineralogy.In addition,crop straw is often incorporated with soil tillage to maintain soil organic carbon（SOC）.Both the crop straw addition per se and its associated soil structure changes can stimulate SOC decomposition,yet no attempt has been made to isolate their effects and underlying microbial processes.The main objective of this study is to identify the influence of clay mineral types and soil structure change on decomposition of crop straw,formation of soil organic matter and their control mechanism,respectively.It will provide scientific basis for undersanding regulation mechanism of soil organic matter and optimizing straw mulching technology.In the experiment of mineral types influencing the crop straw decomposition and soil organic matter formation,（1）we developed a novel model to quantify mineral-organic association strength through CO₂ emission and demonstrated that it was well predicted for a natural soil from its clay mineralogy.（2）And we found that the mineral-associated organic matter included labile（O-alkyl）and recalcitrant litter components and fungal and bacterial residues.（3）We also showed that,in comparision with kaolinite and illite,vermiculite contains more labile components and only fungal residues through surface coating with stronger mineral-organic association strength;vice versus,kaolinite and illite contains more recalcitrant litter components and bacterial residues through pore entrapment.（4）Thus,we concluded that SOM forms from litter decomposition in a mineral soil through two mineral modulated stages.Litter-and microbial residues were randomly associated with clay minerals at the early mineral association stage but selectively preserved by clay minerals at the later mineral protection stage due to different mineral-organic association mechanisms and strengths.In the experiment of isolating the effects of crop straw addition and soil structure changes on soil organic matter decomposition,（1）we manipulated soil texture and increased the>74μm macroporosity of the texture-manipulated soil after crop straw addition.（2）Then we evaluated the effects of the addition of pulse-labeled straw on the priming effects and demonstrated that the easily extracted straw metabolites were labled,which could be suitable used in our short-term incubation experiment.（3）We also used the end mixing model（EMM）based on theδ¹³C abundance to calculate the priming effect induced by crop straw addition and soil structure change.And we showed that crop straw decomposition and total priming effect in the experimental treatment were larger than those in the control treatment by 175%and 170%,isolating the the relative effects of soil structure and crop straw addition for the first time.（4）We further verified the reliablity of the research results using the improved priming model（PRIM）based on CENTRUY model.Our findings highlighted that the formation and decomposition of soil organicmatter is not only driven by biological factors,but also controlled by non-biophysical factors such as mineral types and soil strucure changes.And these factors are not fully considered in existing soil organic matter models,more attention should be paid to the future research.