Microbial community diversity in the rhizosphere of wetland plants examined by phospholipid fatty acid and polymerase chain reaction denaturing gradient gel electrophoresis

Aims Our objective was to investigate the effect of plant growth pattern (single or mixed) of two emergent plants (i.e., Phragmites australis and Typha orientalis) on the microbial biomass and community structure of the rhizosphere in two adjacent shallow lakes in Tianjin, China.
Methods The microbial biomass and community structure were assayed by using phospholipid fatty acid (PLFA) and polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) techniques. Cluster analysis of the microbial PLFA pro?les was performed using hierarchical clustering according to the between-groups linkage method using the software package SPSS 13.0 for Windows.
Important findings The PLFA results showed that microbial biomass in the plant rhizosphere was higher than those in the non-rhizosphere, except for the P. australis rhizosphere in Aiwan Lake. The microbial biomass was significantly higher in the T. orientalis rhizosphere sediments than that in the P. australis rhizosphere sediments in both lakes. The microbial biomass of the same plant’s rhizosphere was influenced by pattern of plant growth (single or mixed). As the growth condition (plant height) was similar in the two lakes, there was only minor difference in the microbial biomass of the T. orientalis rhizosphere. When the two plants grew together, the growth of P. australis was significantly inhibited, and significantly lower microbial biomass was assayed than that under the separated growing condition. The gram-positive bacteria (G⁺) were less than that of the gram-negative bacteria (G^-) in all samples. Moreover, the ratio of G⁺ to G^-in the plant rhizosphere was less than in the non-rhizosphere. Microbial community structure was found to be related to the plant species. Little difference in microbial community structure was observed in same plant rhizosphere sediments between the two lakes; however, apparent differences in the bacterial community were detected between the two different plant species.