| The Loess Plateau of northwestern China is a region where the agriculture production was extremely low due to the infertile soil and drought.Thus,how to improve the yield of crops meanwhile maintain the soil fertility is essential for the agriculture in this region.A long-term fertilization experimental station which has six treatments including of N(inorganic N),NP(inorganic N and P),SNP(straw,inorganic N and P),M(farmyard manure),MNP(farmyard manure,inorganic N and P) and CK(no fertilization),was established in 1979 at Gaoping village of Pingliang,Gansu province,being used for estimate the long-term effects of different fertilization and maize-wheat rotation regimes on the rain-fed agriculture production. Although some previous studies showed that the yield of crops was significantly improved by some fertilization treatments in this station,some important soil microorganisms,like ammonia oxidizing bacteria (AOB),pesudomonas,and arbuscular mycorrhizal fungi(AMF),that highly related to soil fertility and plant healthy has not been investigated.To explore the long-term impact of organic and inorganic fertilizers on microbial diversity and community structure,we employed the polymerase chain reaction(PCR),denaturing gradient gel electrophoresis(DGGE), cloning,and sequencing method to assess the community structure of the total bacteria,AOB,pseudomonas, and AMF;Samples were collected during different growing period of wheat(Triticum aestivum L.) from a rainfed experimental field site.We found that the soil added MNP has the highest fertility level,the CK has the lowest.Meanwhile,the soil fertility level of MNP and M,NP and SNP,N and CK were similar each other respectively.The community analysis were based on sequences that retrieved from the gel bands generated by specific PCR of 16S rRNA for total bacteria,amoA genes for AOB,and 18S rRNA for AMF.Most of the bacteria phylotype belong to the phylum Bacteroidetes and Proteobacteria,the members of the phylum Firmicutes,Actinobacteria,and Gemmatimonadetes appeared simultaneously.The dominant group were more similar to the genera Klebsiella and Delfiia.Phylogenetic analysis of AOB showed that the dominance of Nitrosospira cluster 3.Interestingly,most of the sequences are more similar to those derived from the published data that retained from fertilized soil in China. The analysis of Pseudomonas community structure suggested that the application of organic fertilizer(including Manure or Straw) can lead a abundance changing of some species.Most of phylotypes are similar to the common species Pseudomonas fluorescens and Pseudomonas putida。However,the diversity of AMF was low in our study field.BLAST similarity research demonstrated the overwhelming dominance of Glomus-like ribotypes affiliated to a cultured Glomus species,Glomus mosseae. Through the CCA analysis,we found that the community structure of the total bacteria and AOB were greatly shifted in the different fertilization treatments.But the community of AMF was less sensitive to these different fertilization regimes.The addition of Farmyard manure(M) and chemical fertilizer(N,P) seemed more helpful for the improvement of microbial diversity in these arid agro-ecosystems when compared with the CK treatment.The yield of wheat ranged from 1732 kg ha-1(CK) to 5620 kg ha-1(MNP).One way ANOVA suggested the significant difference(P＜0.05) among the different treatments except those received the NP(insignificant each other).In a word,we conclude that(1):The soil fertility level was greatly influenced by the Long-term local addition of fertilizer,especially by the farmyard manure.(2):The community structure of the total bacteria and the AOB can be greatly influenced by the different fertilization regimes;whereas,the AMF community responded less to these different treatments.Changes in bacterial community composition and a reduction in bacterial taxon richness throughout the growing season were also manifest.(3):Soil moisture and pH contributed more to the variation of microbial community composition than soil organic carbon and total nitrogen content in the arid land of Loess Plateau typical agro-ecosystem.(4):Wheat yield responded intensely for the different fertilizer treatment.Consequently,balanced fertilization (MNP) is an important way for the region's food security and ecosystem harmony.Thus,we proposed that more functional guilds can be selected as the indicators for the microbial ecology research in future.And more powerful statistic tools can be used for the reliable results and better linkage between microbial community structure and agro-ecosystem function.
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