Soil Organic Carbon Mineralization Properties Of Typical Quercus Forest And The Corresponding Microbial Mechanism

Soil organic carbon plays an important role in carbon transformation in global biological system due to its tremendous C stock.Soil organic carbon mineralization is the most important biochemistry process,directly influencing soil nutrient element circulation and greenhouse gases release,and a small change in soil carbon concentration will lead to great changes in atmospheric CO₂ content.Thereby,the study of soil organic carbon mineralization characteristic and its mechanism will help to understand the mechanism of soil carbon circulation.Quercus forest,one of the most common broad-leaved forests in the north of our country,is usually researched due to its large floor space and huge soil carbon stock.In this study,we choose three Quercus Mongolia forests of different ages: QM20 yr,QM30yr and QM40 yr stands in Liaoning province and one 60-year Quercus Acutissima forest?QA60yr?in Shandong province.Then we analyze the soil organic carbon mineralization characteristic,and discuss its mechanism on the level of molecular through soil physicochemical properties,biological performance and microbial community.Our study provides basic scientific evidence for typical Quercus forest soil organic carbon mineralization and that in the global biological system under the circumstance of greenhouse effect.The main conclusions are as follows:1.During a 63-day laboratory incubation,the QM30 yr stand soil has the lowest C0(-104.161 CO₂-C mg g^-1 dwt soil)and a relatively smaller labile carbon content.Moreover,it shows a higher microbial entropy?MBC/SOC?and a higher microbial carbon assimilation ratio.While in the QM20 yr stand soil,it shows the highest C0(67.916 CO₂-C mg g^-1 dwt soil)and a large amount of labile carbon.Its DOC/SOC and EOC/SOC are both higher than other soils,and the microbial assimilation ratio is also higher than other soils.2.Soil cation exchange capacity?CEC?,fungal Chao1 index and Bacterial Chao1 index significantly influence C0 in typical Quercus Mongolia and Quercus Acutissima soils.These values showed negative relationship with C0.The influence degree ranks as: fungal Chao1 index > Bacterial Chao1 index > CEC.3.The QM30 yr stand soil has the lowest SOC mineralization potential(-104.161 CO₂-C mg g^-1 dwt soil)and QM20 yr has the highest one(67.916 CO₂-C mg g^-1 dwt soil).Moreover,soil microbial community composition shows significant influence on SOC mineralization potential.On the level of molecular level,we can find that the soil microbial community develop from bacteria-dominant to a fungicide-dominant community in the succession of Quercus Mongolia forest,indicating that the bacterium is gradually replaced by fungus.According to the relative abundance of bacterial phylum,we can find that the relative abundance of Actinobacteria and Proteobacteria,which tend to decompose old and fresh soil organic matter respectively,are the highest in the QA60 yr stand,indicating a higher tendency for the microorganism to decompose organic matter.The relative abundance of these two phylum bacterium in Quercus Mongolia forest soils ranks as: QM20 yr > QM30 yr > QM40 yr.The QM30 yr stand soil contains a large number of Basidiomycetes in fungal community.The QM40 yr and QA60 yr stand soil has the highest relative abundance in the two main saccharomycetes genus,which shows higher ability to decompose cellulose.4.In the treatments of adding monomer?MN?,polymonomer?PM?,monomer and polymonomer?MIX?,the Q10-SIR is smaller than Q10-BR or Q10-SGR in both of the four Quercus forest soils,and the value of Q10-SIR is around 1.0.During the period of BR,there is no significant difference among the four soils under the same treatment.During the period of SIR,the Q10 in QM40yr?0.9790?is significantly lower than other soils?QM20yr,1.0836;QM30yr,0.9954;QA60yr,1.0409?under the treatment of MN,and the Q10 in QM30yr?0.97103?is significantly lower than other soils?QM20yr,0.9947;QM40yr,1.0152;QA60yr,0.9948?under the treatment of PM.The value of Q10 shows no significant difference among the four soils under the treatment of MIX.