Community composition and activity of anaerobic ammonium oxidation bacteria in the rhizosphere of salt marsh grass Spartina alterniflora
Anaerobic ammonium oxidation (anammox) as an important nitrogen removal pathway has been investigated in intertidal marshes. However, the rhizosphere driven anammox process in these ecosystems is largely overlooked so far. In this study, the community dynamics and activities of anammox bacteria in the rhizosphere and non rhizosphere sediments of salt marsh grass Spartina alterniflora (a widely distributed plant in estuaries and intertidal ecosystems) were investigated using clone library analysis, quantitative PCR assay, and isotope tracing technique. Phylogenetic analysis showed that anammox bacterial diversity was higher in the non rhizosphere sediments (Scalindua and Kuenenia) compared with the rhizosphere zone (only Scalindua genus) Higher abundance of anammox bacteria was detected in the rhizosphere (6.46 x 106 1.56 x 107 copies g 1) which was about 1.5 fold higher in comparison with that in the non rhizosphere zone (4.22 x 106 1.12 x 107 copies g 1) Nitrogen isotope tracing experiments indicated that the anammox process in the rhizosphere contributed to 12 14 N2 generation with rates of 0.43 1.58 nmol N g 1 h 1, while anammox activity in the non rhizosphere zone contributed to only 4 7 N2 production with significantly lower activities (0.28 0.83 nmol N g 1 h 1) Overall, we propose that the rhizosphere microenvironment in intertidal marshes might provide a favorable niche for anammox bacteria and thus plays an important role in nitrogen cycling.
Applied Microbiology and Biotechnology