Soil Microbial Diversity And Plant Growth Promoting Rhizobacteria Resources Of Dominant Plants In Different Degraded Grassland Of Abandoned Land In Minqin

As an important part of the terrestrial ecosystems,the soil microbial plays an important role in a variety of ecological processes,including formation and development of soil,transformation of organic matter,balance of ecosystems,environmental purification and bio-remediation of soil.The soil microbial make effect on the environment largely through the differences of community metabolism.Changes in the diversity of microbial communities not only can reflect the changes of soil quality in prior,but also provide earlier signs of ecological environment evolution.Therefore,it's meaningful to elucidate the effect of microbial communities in different environment and the influence of their structure and function in the ecosystems.Shiyang river basin had an important role in ecological security of country.In recent decades,ecosystem affected by drought and desertification have been on the edge of the crash,because of appearance of large areas of farmland back/abandoned,which had changed to be vegetation secondary grassland and already provoked people's attention.A large of researches about ecological remediation had been done,but there is still a lack of research on soil microorganisms.This paper focus on the study of soil microbial diversity and potential PGPR,which can offer practice and theoretical basis on protection and restoration of vegetation secondary grassland.This paper chose the Minqin oases abandoned land in four different years of secondary grassland(1a?5a?10a and the land without cultivation)and roots of dominant plant in Shiyang river basin as the research object.On one hand,in order to research the interaction mechanism of microbial diversity of bacteria and fungi,we selected four abandoned land under different years with the method of space-time substitution approach,and collected the soil from different layer(0-20 cm,20-40cm),analyzed the diversity of bacteria and fungi though the high throughput sequencing.On the other hand,we collected roots of five dominate plants(Kalidium oliatum(Pall.)Moq,Peganum harmala,Purple nutsedge,Halogeton glomeratus and Lycium ruthenicum Murr)in different years of abandoned land.Though separation,purification and screening of strain PGPR,to got potential PGPR,which had capacity of nitrogen fixation and phosphate-solubilization.To identify potential PGPR by physiology and biochemistry characteristics and 16 S rDNA sequence analysis.The results were obtained as follows:1.On the study of bacteria diversity in soil: there were 746879 high quality sequences acquired though sequencing;The quantity of OTU were reduced with the extension of classification levels in 8 soil samples,which contained 931 common OTU;To analyze the rarefaction curves,the OTU numbers in abandoned land of one year were the most.Except not cultivated land,the soil layer(0-20cm)had more OTU than soil layer(20-40cm);Rank-abundance curve showed that all of the soil samples were similar to each other;Through the calculation of diversity index Chao1,ACE,Shannon and Simpson,the soil in abandoned land of one year were the highest,the variation trends of microbial abundance and diversity were similar between different soil samples;There were no obvious difference between all of the soil samples though calculated the diversity index;The results of PCA and cluster analysis showed that sample in not cultivated land had very obvious differences to the other soil samples,and the distance in different sample groups were bigger than the each group;The soil samples had 196,616,834,1065,1094 and 349 bacteria population,respectively,under six different classification levels.The species of dominant bacteria were the same basically in 8 soil samples,mainly by Actinobacteria,Proteobacteria,Chloroflexi,Gemmatimonadetes,Acidobacteria,Planctomycetes and Bacteroidetes on the level of“Phylum”,and Planctomyces sp.,Bacillus sp.,Euzebya sp.,Streptomyces sp.on the level of“Genus”;There were more than 37 kinds functional genes in 6 classes in soil samples,which were environmental information processing,metabolism,cellular processes,genetic information processing,organismal systems and human diseases,the genes of metabolism were the most.Through analysis of different functional genes,we realized that no obvious regularity in the distribution of functional genes.2.On the study of fungi diversity in soil: there were 557313 high quality sequences though sequencing.The rarefaction curves showed that the OTU in abandoned land of ten years was the most,which meant fungi diversity was the highest in it.In addition to the abandoned land of one years,the quantity of OTU in the soil layer(20-40cm)were more than soil layer(0-20cm);To calculated the samples of diversity index,such as Chao1,ACE,Shannon and Simpson,which showed that the index in abandoned land of ten year was the highest,and there was a little difference in the other samples;The result of PCA indicated two soil samples in the same year had a few difference,and the composition in abandoned land of one years were not similar to the others;Two soil samples of one year could be divided to one group though cluster analysis;Analysis of the fungi species in evolutionary,there were 4 dominant species(Ascomycota,Basidiomycota,Zygomycota Chytridiomycota)on the level of “Phylum”,and Ascomycota had higher proportion among them,especially in abandoned land of one year,and each abandoned land had special fungi species respectively,which had huge difference in abundance.What's more,there were 4 dominat species(Pseudogymnoascus sp.,Microascus sp.,Acremonium sp.,Penicillium sp.)on the level of“Genus”.In the network of fungi,most of fungi species were interacted with each other,but there were five groups species had the one-to-one relationship(Rubinoboletus sp.And Phoma sp.,Aspergillus sp.and Micriascus sp.,Coniocessia sp.and Solorina sp.,Mortierlla sp.and Acremonium sp.,Chaetomium sp.and Monosporascus sp.).3.Though conventional bacteria separation methods,there were 320 strains were isolated from the rhizosphere of five tested plants rhizosphere soils in different abandoned land.There were 115 strains nitrogen fixing bacteria,107 strains soluble inorganic phosphorus strains and 98 strains dissolving organic phosphorus strains.The number of bacteria was presented as RS(root soil)> RP(rhizoplan or surface of roots)> HP(histoplan or interior of roots),showing an obvious rhizosphere effect.4.Researching on the growth characteristic of PGPR strain: the results indicated that39 strains had good nitrogenase activity,which nitrogenase activity varied from 23.13 to559.68 nmolC2H4·h-1mL-1,and 20 strains higher than 300nmolC2H4·h-1m L-1,the NCHP1 strain from Halogeton glomeratus was the best among them.There were 50 strains had good ability of inorganic phosphate solubilizing,which were varied from 19.55 to 574.40 ?g·mL-1,and 22 strains reached 300.0.?g·mL-1that accounted for 44% of all.The NDRP2 strain was the best among them.While 37 organic phosphate solubilizing bacteria strains had been chose,the amount of dissolved phosphorus in 27.79~429.389 ?g·mL-1,and 10 strains reached 300.0.?g·mL-1,which accounted for 27.03% of all,the NDRS1 strain had the highest phosphate solubilization capacity.5.There were 21 selected strains were identified based on 16 S rDNA,which belonged to 4 genus and 7 species.After research on characteristics of the promotion,there were 15 potential PGPR strains had the potential to develop,which included 5 Bacillus pumilus strains,6 Bacillus subtilis strains,2 Serratia rubidaea strains,Bacillus cereus and Bacillus siamensis had each one strain.