Effects of different forms of nitrogen on rhizosphere microbial community structure of Eichhornia crassipes (Pontederiaceae).

Rhizosphere microbial communities are important for phytoremediation, plant nutrition, health and metabolism. Many factors, including plant species, pH and nutritional factors influence rhizosphere micro- biology. In this study, we analysed the effects of different forms of nitrogen on the structures of rhizosphere microbial communities of E. crassipes. Using a conventional culture method with special media, bacteria, acti- nobacteria and molds were cultured. We found that the numbers of bacteria were largely similar across the three culture conditions, while the numbers of actinobacteria and molds from the rhizosphere of E. crassipes cultured in NH4Cl solution were two orders of magnitude higher than those from the rhizospheres of plants cultured in distilled water and KNO3 solution. Using a culture-independent method of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rDNA, we found that the form of nitrogen could influence the components of the rhizosphere microbial community. Pseudoxanthomonas, Enterobacter and Citrobacter were present in all of the samples cultured under the three different experimental conditions. The genus Reyranella was found only in samples cultured in KNO(3) solution; Acinetobacter and Streptomyces were unique to samples cultured in NH(4)Cl solution, and Pseudomonas, Pseudacidovorax and Methylosinus were found only in samples cultured in distilled water. Pseudoxanthomonas and Acidovorax were the dominant genera in the rhizosphere microbial community of E. crassipes cultured in KNO(3) solution, while Novosphingobium was the dominant genus in the sample cultured in a nitrogen-deficient medium. Our results provide a theoretical foundation for using E. crassipes as a phytoremediation plant and controlling the widespread distribution of E. crassipes around the world using principles of nutrient metabolism.