Study Of Impact On Soil Microbial Community In Eucalyptus Plantation

Eucalyptus grows for wood and fiber productions in almost all the tropical and subtropical areas.Eucalyptus plantation has been controversial because of its influence to the surrounding environments and ecosystem.However,it is unclear about the influence of massive Eucalyptus planting to soil microbial communities.Soil microbies as the vital part of soil ecosystem take on the function of nutrient cycling and toxin degradation etc.Meanwhile,soil microorganism are prone to be influenced by vegetation and soil properties in terrestrial ecosystem.In order to detect the impact on soil microbial communities in Eucalyptus plantation,we used the wet-sieve method and high-throughput sequencing of 16 s RNA gene to assess the composition and structure of AM fungi and bacteria communities,as well as the prediction of functional profiles according to PICRUSt.Then we found the differences between samples to explore the influence on soil ecosystem brought about by Eucalyptus plantation.Additionally,we added Eucalyptus litters into soil in secondary-forest and contrast soil microbial community among samples collected after three and six months,which can illustrate the variation of microbes produced by litters.The major results are list as followed:(1)The planting of Eucalyptus changed the physical and chemical properties of soil.The changes of different physical and chemical factors in different planting years were different,including soil pH,organic carbon and ammonium nitrogen,which decreased significantly in the second and tenth years.Total potassium in soil decreased gradually in early planting period,but increased significantly in the tenth year and keep it at a certain level.The planting of Eucalyptus significantly reduced the spore density and species abundance of AM fungi in soil,but recovered in the tenth year.The community composition and structure of AM fungi were changed significantly and varied with the increase of planting years.The planting of Eucalyptus did not change the dominant genus.The genus of Acaulospora and funneliforms were dominant genera in secondary and Eucalyptus forests.Dominant species F.geosporus increased markedly during the second and tenth years of Eucalyptus plantation.S.deserticola increased significantly after Eucalyptus cultivation,while the year five was significantly lower than in the second and tenth years.Pacispora.sp1 and Scutellospora.sp1 only existed in secondary forests,while disappeared in Eucalyptus plantations.When Eucalyptus was planted,the diversity of AM fungi community was not changed significantly.The community structure was most affected by soil pH value,followed by total N and total potassium.(2)The planting of Eucalyptus did not change the diversity of soil bacteria.The species abundance increased significantly compared with secondary forest during the five-year planting.However,the planting of Eucalyptus changed the composition and structure of soil bacterial community,and it was significantly different from that in secondary forest.At the phylum level,the relative abundance of Actinobacteria and Firmicutes in soil increased in the second year of planting,but decreased significantly in the fifth year.Cyanobacteria and Tm6_dependentiae significantly decreased after Eucalyptus plantation,but there was no significant variation with the increasing planting years.Gemmatimonadetes increased significantly in the second and tenth years after Eucalyptus plantation.Under the genus level,relative abundance of roseiarcus,acidobacterium,and Unclassified_f_acetobacteraceae decreased significantly during the five year of Eucalyptus plantation compared with secondary forest.Soil available phosphorus,available potassium,pH,ammonium nitrogen are the main factors affecting the bacterial community.The results of functional prediction showed that nitrogen metabolism,amino acid metabolism and lipid(compound)metabolism were significantly higher than that in secondary forest and in the second and tenth years of Eucalyptus plantation.After Eucalyptus plantation,the adjuvant factor and vitamin metabolism decreased significantly.(3)The Eucalyptus litter increased the soil organic carbon,total nitrogen and total phosphorus,but the pH,ammonium nitrogen,nitrate nitrogen did not change significantly in six months.The addition of litter increased the spore density of AM fungi firstly,but the species abundance increased first and then decreased.Eucalyptus litter made soil AM fungi community structure changed.Dominant species F.geosporus first decreased and then recovered.A.spinosa and R.gregaria increased significantly after litter placement.At the same time,litter reduced the diversity of AM fungi community in soil,of which factors are total nitrogen,total phosphorus,organic carbon,ammonium nitrogen,etc.(4)The addition of Eucalyptus litter significantly changed the composition and structure of soil bacterial communities.The number of OTU decreased with the increase of placement time,and the diversity of bacterial communities decreased significantly during the sixth month.New OTU appeared in litter soil at three months and six months respectively.At the phylum level,the relative abundance of Acidobacteria and Firmicutes significantly increased after litter treatment of six months.The relative abundance of chloroflexi and GAL15 significantly decreased after litter treatment of six months.At the genus level,Da111_norank,HSB Of53-f07_norank and Variibacter,etc.were significantly reduced after six months.Total nitrogen,total phosphorus and organic carbon in soil are important factors affecting bacterial community structure,and have positive correlation with bacteria.The results of functional prediction showed that nitrogen metabolism,amino acid metabolism,carbohydrate biosynthesis and metabolism decreased significantly in the early stage of placement,and methane metabolism decreased significantly during six months of litter addition.