Effects Of Clay Minerals On Straw Degradation And Agglomeration Formation

The interaction between soil minerals and microorganisms is an important ecological process in the earth's surface system.Soil microorganisms play an important role in element cycling,mineral formation and weathering in terrestrial ecosystems.At the same time,the number,activity,diversity of community structure and expression of functional genes of microorganisms are closely related to mineral types and compositions.The mineral particles in the soil are small and have huge specific surface area and surface energy.It can absorb and fix soil microorganisms,control the survival and migration of microorganisms in the soil,and restrict the activity and function of soil microorganisms.Therefore,this research focuses on the soil clay mineral-microbial mechanism,using straw and soil minerals(montmorillonite,kaolinite,quartz)as materials,through indoor simulated culture experiments to study the effects of clay minerals on microbial biomass,enzymatic activity of extracellular enzymes and relative abundance of functional genes during the degradation of straw,and then to further explore the effects of microorganisms on the turnover and aggregate formation of organic carbon.The main results are as follows:(1)During the ongoing straw decomposition,the content of organic carbon in artificial soil decreased significantly.The content of organic carbon in artificial soil with montmorillonite treatment decreased from 14.9 mg/g to 8.7 mg/g,and it in artificial soil with kaolinite treatment decreased from 14.9 mg/g to 7.7 mg/g.The content of soluble organic matter decreased from 0.64 mg/g to 0.28 mg/g in artificial soil with kaolinite treatment and from 0.45 mg/g to 0.37 mg/g in artificial soil with montmorillonite treatment,indicating that the ability of montmorillonite to stabilize organic carbon was higher than that of kaolinite treatment.(2)In the process of straw degradation,microbial biomass carbon first increased and then decreased,reaching its peak value on the seventh day of cultivation.The maximum microbial biomass carbon of different clay minerals was 0.57 mg/g(montmorillonite)and 0.73 mg/g(kaolinite),respectively,which indicated that montmorillonite treatment had stronger inhibition ability to microorganisms.The activity of extracellular enzymes secreted by microorganisms increased firstly and then decreased.The activity of extracellular enzymes was ?-1,4-D-glucosidase(BG)and cellobiohydrolase(CBH)> beta-1,4-N-acetylglucosaminidase(NAG)> acid phosphatase(AP).The activity of extracellular enzymes in different clay minerals was significantly different.The activity of extracellular enzymes in kaolinite was higher than that in montmorillonite.The relative abundance of microbial bacteria showed a downward trend,while that of fungi increased first and then decreased.This indicated that bacteria played a major role in the degradation of straw in the early stage of cultivation,while fungi played a dominant role in the middle and late stage of cultivation.The relative abundance of CBHI gene increased first and then decreased during the culture period,reaching its peak on the seventh day of culture.The relative abundance of functional microorganisms in kaolinite treatment was significantly higher than that in montmorillonite treatment,indicating that kaolinite was more conducive to the growth and reproduction of functional microorganisms of straw degradation.(3)In the process of straw degradation,the content of aggregates with different particle sizes changed significantly.The average weight diameter MWD of montmorillonite treatment increased first and then decreased,from 1.04 mm(Day 1)to 1.50 mm(Day 7),and finally to 1.22 mm(Day 360).The average weight diameter(MWD)of kaolinite treatment increased steadily from 1.48 mm(Day 1)to 1.69 mm(Day 360).The proportion of macroaggregates of > 2 mm in montmorillonite treatment is 24.14-50.24%,and the proportion of macroaggregates of > 2 mm in kaolinite treatment is 46.02-78.66%,which indicates that kaolinite is more conducive to the formation of macroaggregates.(4)In the process of straw degradation,the content of organic carbon in macroaggregates of > 0.25 mm decreased gradually,while the content of organic carbon in small aggregates of < 0.25 mm increased first and then decreased.The trend of both montmorillonite treatment and kaolinite treatment was the same.The organic carbon content of the macroaggregates of >2 mm treated with montmorillonite decreased from 16.07 mg/g to 9.20 mg/g,with a decrease rate of 42.75%.The organic carbon content of the macroaggregates of >2 mm treated with kaolinite decreased from 17.50 mg/g to 6.97 mg/g,with a decrease rate of 60.17%.It is obvious that the organic carbon content of the macroaggregates of > 2 mm treated with kaolinite decreased more significantly,indicating that the organic carbon in the macroaggregates treated with kaolinite is more easily mineralized.The change trend of organic carbon content in aggregates of 0.25-2 mm was consistent with that in aggregates of > 2 mm.In microaggregates of < 0.053 mm,the content of organic carbon treated with montmorillonite increased from 8.20 mg/g to 23.65 mg/g,and then decreased to 6.58 mg/g,and that treated with kaolinite increased from 14.80 mg/g to 28.67 mg/g,and then decreased to 12.25 mg/g.The results showed that the metabolites of microorganisms were mainly concentrated in aggregates of < 0.053 mm.