Studies On The Changes Of Microbial Community Composition And Structure In Evolution Process Of Paddy Soil

Soil chronosequences are valuable tools for investigating the rate and direction of soils development.There are many successful reports using different chronosequences.However few reports are related to paddy soils.Inundation of paddy soils for submerged rice production strongly impacts soil formation.Here we used two chronosequences with different cultivation history from Shangyu(cultivation time 10-30 years)and Cixi(cultivation time 50-2000 years)to compare soil formation between paddy and upland cropping systems.Thus,the thesis is stringed along microbial community composition and structure to study the influence of paddy management on microbial quantity,composition,diversity and taxonomic shifts at different stages of pedogenesis.The following results were obtained:1.Physicochemical characteristics.Paddy soil EC and total potassium decreased with increased duration of rice paddy cultivation in Shangyu(S Y)and Cixi(CX)chronosequence.But rice cropping increased soil organic carbon(SOC)and total nitrogen(Ntot).Compared to the reference site,SOC and Ntot in 30-year paddy soil(SY)increased 5.2 and 0.21 g kg-1,while 2000-year paddy soil(CX)increased 19.4 and 2.0 g kg-1,respectively.Soils developing under upland management showed a slower desalinization.Soil EC in upland soil(SY)was higher than paddy soil,while there were no significant difference between paddy and upland soil in Cixi chronosequence.Compared to upland,paddy soil management tends to increase SOC and Ttot.2.Hydrolase enzymes activity.Paddy soil urease,phosphatase,arysulfatase and dehydrogenase activites increased with increased duration of rice paddy cultivation in S Y and CX chronosequence.Soil enzyme activities were positively correlated with soil cultivation ages.Paddy soil enzyme activities were similar to those of upland soil in SY chronosequence.Paddy soil dehydrogenase,arysulfatase and ?-glucosidase activites were higher than upland soil in CX chronosequence,while catalase,urease and phosphatase were similar.3.Soil bacteria and fungi quantity.There was positive correlation between microbial quantity and soil cultivation age.There was no significant difference in bacterial and fungi quantity between paddy soil and upland in S Y chronosequence.However,fungi quantity in paddy soil was higher than that in upland soil in CX chronosequence.4.PLFA profiling.PLFA composition was different between two chronosequence,but both paddy soils contain high PLFAs.Compared to the reference site,paddy soil management in SY chronosequence tend to increase bacterial PLFA ratio and decrease fungi PLFA ratio.Soil age did not influence the bacterial PLFA ratio,but had negative correlation with fungi PLFA ratio in CX chronosequence.The ratio of gram positive bacteria to gram negative bacteria in paddy soil were generally found to be lower than upland soil in both chronosequence.5.Soil bacteria and fungi diversity.Soil cultivation age had positive correlation with bacterial diversity,but did not influence fungal diverstiy in SY chronosequence.Soil cultivation age had negative correlation with fungal diversity,but did not influence bacterial diverstiy in CX chronosequence.Compared to upland soil,paddy soil management(SY)tends to increase bacterial diversity,while paddy soil management(CX)tends to decrease fungal diversity.Soil EC,SOC and Ntot are major contributors to the distribution of soil microbes in this study.6.Miseq sequencing.The dominant phyla across all samples were Proteobacteria,Acidobacteria,Bacteroidetes,Verrucomicrobia,Actinobacteria and Firmicutes.The major microbial community structures were different among SY and CX chronosequence.The dominant fungal phyla in all samples were Ascomycota,Chytridiomycota,Basidiomycota,Glomeromycota and Zygomycota.Soil EC,pH and SOC are major contributors to the distribution of soil bacteria in paddy chronosequence,while soil type and N are major contributors to the distribution of soil fungi in paddy chronosequence.Correlation analysis showed that higher soil total nitrogen related to long-term cultivation was associated with lower Proteobacteria and Ascomycota,but higher Verrucomicrobia.The results showed that the response of soil bacterial community was correlated with the reclamation history.