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Zhou J.,Chinese Academy of Agricultural Sciences | Zhou J.,China Agricultural University | Jiang X.,Chinese Academy of Agricultural Sciences | Jiang X.,Laboratory of Quality Safety Risk Assessment for Microbial Products Beijing | And 12 more authors.
Soil Biology and Biochemistry | Year: 2016

Black soil is one of the main soil types in northeast China, and plays an important role in Chinese crop production. However, nitrogen inputs over 50 years have led to reduced black soil fertility. It is unclear how N affects the fungal community in this soil type, so a long-term fertilizer experiment was begun in 1980 and we applied 454 pyrosequencing and quantitative PCR to targeted fungal ITS genes. There were five treatments: control (no fertilizer), N1 (low nitrogen fertilizer), N2 (high nitrogen fertilizer), N1P1 (low nitrogen plus low phosphorus fertilizers) and N2P2 (high nitrogen plus high phosphorus fertilizers). Soil nutrient concentrations (Total N, Avail N, NO3 -, NH4 +, etc.) and ITS gene copy numbers increased, whereas soil pH and fungal diversity decreased in all the fertilized treatments. Relationships between soil parameters and fungal communities were evaluated. Dothideomycetes, Eurotiomycetes, Leotiomycetes, Sordariomycetes, and Agaricomycetes were the most abundant classes in all soils. Principal coordinates analysis showed that the fungal communities in the control and lower-fertilizer treatments clustered closely and were separated from communities where more concentrated fertilizers were used. Fungal diversity and ITS gene copy number were dependent on soil pH. Our findings suggested that long-term nitrogen and phosphorous fertilizer regimes reduced fungal biodiversity and changed community composition. The influence of the more concentrated fertilizer treatments was greater than the lower concentrations. © 2015 Elsevier Ltd.

Liu Y.,Chinese Academy of Agricultural Sciences | Guan D.,Chinese Academy of Agricultural Sciences | Jiang X.,Chinese Academy of Agricultural Sciences | Ma M.,Chinese Academy of Agricultural Sciences | And 6 more authors.
Biology and Fertility of Soils | Year: 2014

Competitiveness for nodulation is one of the major restrictive factors in symbiotic nitrogen fixation between rhizobia and their host legumes. Soybean root exudates that include a variety of compounds are thought to act as signals to trigger the early symbiotic events between Bradyrhizobium diazoefficiens and soybeans, and thus they act as a key determinant of the competitiveness for nodulation. To gain a better understanding of the molecular mechanism of competitiveness at the level of protein expression, we compared the proteomic responses of two B. diazoefficiens strains that demonstrated completely different nodulation abilities, strain 4534 being the most competitive and strain 4222 being the least competitive in nodulation. In the proteomic analysis, 40 of the 65 and 22 of the 29 differential proteins were identified in response to soybean root exudates in strain 4534 and strain 4222, respectively. Compared to strain 4222, a higher amount and a number of differential proteins were detected in strain 4534, including S-adenosylmethionine synthetase (SAMS), PhyR-σEcfG regulon, ABC-type transporters, flagellar proteins, molecular chaperones, and proteins involved in redox state maintenance as well as several unknown proteins. Noteworthy was the induction of the PhyR-σEcfG regulon and flagellar proteins, recently demonstrated to be involved in the competitiveness for nodulation in Bradyrhizobium japonicum. Our results indicate that the role of root exudates can go far beyond inducing the expression of nodulation genes in B. diazoefficiens. Many other proteins/enzymes involved in the metabolism and environmental fitness were also upregulated when exposed to root exudates. More proteins were upregulated by the high nodulation competitive strain than that by the low, and the reasons for this need further investigation. The outcome of such study may contribute to our understanding of molecular mechanisms of different competitiveness in B. diazoefficiens as well as specific adaptation in the legume host. © 2014, Springer-Verlag Berlin Heidelberg.

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