Bacterial Community Composition In Rhizosphere Research Articles

Long-term fertilization changes bacterial diversity and bacterial communities in the maize rhizosphere of Chinese Mollisols

The rhizosphere is a dynamic interface in which interactions among a myriad of microorganisms affect plants growth and tolerance to biotic and abiotic stress. Although rhizosphere effects on soil microbial communities have been widely investigated, few studies have evaluated such impacts of long-term fertilization on rhizosphere microbial communities in black soils common to northeast China. Here, we applied quantitative real-time polymerase chain reaction and high-throughput pyrosequencing to characterize rhizosphere and bulk soil bacterial communities in a long-term (36-year) fertilizer experiment. Soils were subjected to six treatments: CK (no fertilizer), N1 (150 kg urea ha−1 y−1), N2 (300 kg urea ha−1 y−1), M (18,600 kg horse manure ha−1 y−1), NPK (150 kg urea plus 33 kg P plus 62 kg K ha−1 y−1), and MNPK (M plus NPK). Inorganic fertilizer, especially N, decreased the 16S rRNA gene copy numbers and bacterial diversity in the rhizosphere and bulk soil, while manure fertilizer increased these values. Moreover, 16S rRNA gene copy numbers were higher and bacterial diversity was lower in the rhizosphere than the bulk soil, indicating that the maize rhizosphere had significant effects on bacterial diversity. The bacterial communities were predominantly composed of Proteobacteria and Acidobacteria in both the rhizosphere and bulk soil, but the rhizosphere and bulk soil communities were distinguished by principal coordinates analysis. Soil pH correlated with bacterial community composition and diversity in both rhizosphere and bulk soil. However, bacterial community composition in rhizosphere was more correlated with soil nutrient concentrations than in bulk soil under long-term fertilization. A redundancy analysis also indicated that soil pH, organic matter and available phosphorus concentrations were the most important factors in shaping bacterial communities in the maize rhizosphere. Our results revealed that long-term fertilization with increasing nutrients availability increased bacterial abundance, decreased biodiversity and changed bacterial composition in the rhizosphere.

Bacterial Diversity in Mine Tailings Compared by Cultivation and Cultivation-independent Methods and their Resistance to Lead and Cadmium

To examine bacterial community composition in rhizosphere of plants colonizing on mine tailings and phylogenetic differences between subcommunities resistant to different metals, we constructed four clone libraries of 16S rDNA sequences. One was amplified directly from tailing microbial DNA (named as Ci library) and three from cultures on the plates containing of 0.5 mM CdCl(2) (Cd library), 2 mM Pb (NO(3))(2) (Pb library), and without any metals (Cw library). In total, nine bacterial divisions and two unclassified groups were identified from 352 clones of these libraries. Ci clones covered eight divisions, whereas all cultivable clones only covered four divisions. Thus, Ci library provided more phylogenetic diversity than cultivable libraries. However, the microbes represented by the cultivable clones were more similar to previously described bacteria than those represented by Ci clones. All Ci clones were not found in three cultivable libraries. Cd library were exclusively Gram-negative bacteria of Acinetobacter, Ralstonia, Comamonas, and Chryseobacterium. Meanwhile, dominant Gram-positive bacteria in Pb library, Paenibacillus and Bacillus, were also not found in Cd library. Our data indicate that phylogenetic structure was very different from those in acid mine drainage. Meanwhile, tailings harbored phylogenetically distinct subcommunities resistant to Pb and Cd.

Effect of intercropping on crop yield and chemical and microbiological properties in rhizosphere of wheat (Triticum aestivum L.), maize (Zea mays L.), and faba bean (Vicia faba L.)

In this study, we investigated crop yield and various chemical and microbiological properties in rhizosphere of wheat, maize, and faba bean grown in the field solely and intercropped (wheat/faba bean, wheat/maize, and maize/faba bean) in the second and third year after establishment of the cropping systems. In both years, intercropping increased crop yield, changed N and P availability, and affected the microbiological properties in rhizosphere of the three species compared to sole cropping. Generally, intercropping increased microbial biomass C, N, and P availability, whereas it reduced microbial biomass N in rhizosphere of wheat. The rhizosphere bacterial community composition was studied by denaturing gradient gel electrophoresis of 16S rRNA. In the third year of different cropping systems, intercropping significantly changed bacterial community composition in rhizosphere compared with sole cropping, and the effects were most pronounced in the wheat/faba bean intercropping system. The effects were less pronounced in the second year. The results show that intercropping has significant effects on microbiological and chemical properties in the rhizosphere, which may contribute to the yield enhancement by intercropping.