Microorganism Diversity And Community Structure In A Agroecosystem Of Long-term Fertilization

Soil microbes play key roles in ecosystems:they drive major biogeochemical processes and contribute to the maintenance of plant productivity and species richness on earth.The study of soil microbial diversity is the basis for analysis of soil ecosystem function.However,the traditional approaches are feeble to study soil microbial diversity due to its limitations.With the development of molecular methods and its application in microbial ecology,investigation of soil microbial diversity becomes hotspot in studying soil ecosystem function.In this work,microscopic inspection of stained roots and PCR-DGGE technique were utilized to investigate the effects of organic(M)and inorganic(N,NP)fertilizer on the diversity and community structure of soil bacteria and arbuscular mycorrhizal fungi(AMF)in a corn-(Zea mays L.)agroecosystem of long-term(29-year)fertilizer amendments(N,NP,SNP,M, MNP,CK)in Northwest China.The main results were abstracted as follow:1.The percent of AM colonization and spores density have significant difference among soils treated with inorganic fertilizer(N,NP),straw plus N(SNP),manure (M),manure plus N,P(MNP)and unfertilized control(CK).The percent of AM colonization is between 17.3 - 86%and the range of spores density is from 2.4-5.1/g soil.Long-term application of inorganic fertilizers,especially P fertilizers, has a negative impact on spores density,which is more significant than that caused by organic fertilizers.Application of ferilizers contributes to the AM colonization.The result shown that inorganic fertilizers are more powerful than organic fertilizers.The effects of fertilizers on spores density and AM colonization in different seasons were studied.The percent of AM colonization in September is significantly higher than that in June,and the spores density of soil treated with inorganic fertilizers in June is higher than that in September,whereas the effect on those treated with M or MNP and non-treated is conversed.2.The increased content of N and P caused by long-term fertilizer amendments, which changed the soil fertility,may contribute to the change of corn yields. 3.Spores density and percent of AMF colonization were significantly correlated with some soil properties,especially the available P(AP)and K(AK)content of the soil;Corn yeilds increased with increasing soil AP but decreased when spores density of the soil increased,furthermore,no significant correlation with the microbial diversity was observed.4.Our results showed that long-term fertilization could improve soil microbial diversity regardless inorganic or organic fertilizer,but either inorganic or organic fertilizer could do harm to the diversity of AMF,especially the phosphorus.5.Bacterial and AMF community structure were affected by soil management practices,as evidenced by changes in the PCR-DGGE banding patterns.Bacterial and AMF community structure in the M-treated or MNP- treated soil was more closely related to the structure in the untreated soil than that in soils treated with inorganic fertilizers.Seasonal changes in the species compositions of the bacterial and AMF communities as a whole were observed in the different treatment sites.Among the soils tested,a significantly higher number of bacterial ribotypes and a more even distribution of the bacterial community existed in the treatment soil.All of the 33 bacterial clones obtained from the treated soil were assigned taxonomic units which grouped into five major taxa:α-,β-,γ,-,andδ-Proteobacteria(72.7%), HGC(6.1%),LGC(9.1%),CFB(9.1%)and Gemmatimonadetes.Results from this study suggested that bacterial community structure was closely related to other agroecosystem. AMF community structure was also estimated by PCR-DGGE,it showed that the AMF diversity was low in agroecosystem.Only ten AMF species which belong to the genus of Glomus were detected in all samples.In a word,the percent of AM colonization,spores density,microbial diversity and community structure were affected by long-term fertilizer amendments,and inorganic fertilizers have more significant impact,directly or indirectly,than organic fertilizers.