Soil Organic Carbon Mineralization,microbial Communities And Functions In Arable Mollisols With Different Organic Matter Contents

Based on the long-term soil spatial transplant experiments in Hailun Agroecology Experiment Station,Chinese Academy of Sciences and Dehui Mollisols Research Base,together with the in situ samples,the soil organic carbon mineralization and microbial communities in Mollisols with five organic matter contents(SOM1.7,SOM3,SOM5,SOM6 and SOM11)were studied.The characteristics of soil organic carbon mineralization and temperature sensitivity in five arable Mollisols were studied by incubation.Then,based on the spatial transplant experiment in Hailun,PLFA method was used to study the effect of organic matter contents on soil microbial community structure.Furthermore,the responses of bacterial and fungal communities to organic matter content,climate and fertilization were studied by Illumina sequencing technique based on the spatial transplant experiments in Hailun and Dehui,and the soil microbial function was then characterized by enzyme activity.The results are as follows: 1.In Mollisols with five organic carbon contents,the organic carbon mineralization amounts showed the trend of SOM11 > SOM6 > SOM5 > SOM3 > SOM1.7,and the the organic carbon mineralization amounts increased with the increase of incubation temperature.At the initial stage of incubation,the increase of soil organic matter content and incubation temperature led to the acceleration of organic carbon mineralization rate and decreased the temperature sensitivity of soil organic carbon,but at the later stage,the mineralization rate in five Mollisols tended to be the same at 5,15,25 and 35 ?,and the temperature sensitivity of soil organic carbon increased with the increase of soil organic matter content.2.In Mollisols with five organic carbon contents,the total phospholipid fatty acids(PLFAs)ranged from 10.56 to 31.48 nmol/g,the bacterial PLFAs ranged from 6.23 to 18.40 nmol/g,and the fungal PLFAs ranged from 1.78 to 4.57 nmol/g.The total microbial PLFAs,bacterial PLFAs,and fungal PLFAs increased significantly with fertilization and the increase of organic matter content,but there were no significant effects of fertilization and organic matter content on the fungal/bacterial ratio.NMDS and RDA analysis showed that organic matter content,fulvic acid content,total nitrogen content,and fertilization were important factors in contributing to the difference of microbial community structure.3.The dominant bacteria phyla in Mollisols with five organic matter contents were Proteobacteria,Actinobacteria,Acidobacteria,and Chloroflexi,accounting for 80.5% of all sequences.Organic matter content,fertilization,and climate changed the composition of the bacterial community in arable Mollisols,but climate conditions had no significant effect on the structure and relative abundance of functional bacteria groups in arable Mollisols.p H,organic matter content,fertilization,and other soil properties were important factors leading to changes in soil bacterial community structure,and organic matter content and fertilization also caused changes in relative abundance of functional bacteria groups.The bacterial diversity,community structure and functional population in arable Mollisols were resistant to slight climate change.4.The dominant fungi phyla in Mollisols with five organic matter contents were Ascomycota,Basidiomycota,and Zygomycota,accounting for 92.5% of all the sequences.Organic matter content,fertilization,and climate changed the composition,diversity,and structure of the fungal community in arable Mollisols.Organic matter content,climatic conditions,and fertilization also had important effects on the relative abundance of soil functional fungi.For example,the relative abundance of symbiotic fungi decreased with the increase of soil organic matter content,but the relative abundance of symbiotic fungi increased significantly under warmer climatic conditions and fertilization.5.In Mollisols with five organic matter contents,cellulase activities were 1.42?3.67 mg glucose/(kg·72h),?-glucosidase activities were 47.13?296.16 mg phenol /(kg·h),sucrase activities were 22.09?128.52 mg glucose/(kg·24h)and urease activities were 0.12?0.33mg/(kg·24h).The activities of ?-glucosidase,sucrase and urease increased with the increase of soil organic matter content,while that of cellulase showed a downward trend.Fertilization promoted all four enzymes activities in varying degrees.Cellulase,?-glucosidase and urease activities increased under warmer climatic conditions,but sucrose activity decreased.There was a significant correlation between soil enzyme activities and specific soil microbial communities.In summary,soil organic carbon mineralization rates,the structure and function of soil microbial community in Mollisols are significantly affected by soil organic matter content and climatic conditions.The results can provide support for cultivated land conservation and food security in the Mollisols region of Northeast China.