Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2008
Publication Date: 10/1/2008
Citation: Song, Y., Deng, S.P., Acosta Martinez, V., Katsalirou, E. 2008. Characterization of redox-related soil microbial communities along a river floodplain continuum by fatty acid methyl ester (FAME) and 16S rRNA genes. Microbial Ecology. 40(3):499-509. Interpretive Summary: Agricultural production is dependent on healthy soils and soil health is dependent on its microbial communities. How soil microbial communities are affected by soil characteristics, like soil redox state, is poorly understood. Scientists from Oklahoma State University and the ARS location in Lubbock TX evaluated microbial communities in soils with varying degrees of oxygen along the Tisza river floodplain in Hungary. In all the soils tested, microbial communities varied with the frequency of flooding and soil redox state. Mycorrhizal fungi were dominant components (about 12%) of the microbial community in high oxygen soil layers. Abundance of gram-positive bacteria increased with increasing soil depth when shifting from oxic to anoxic (no oxygen present) conditions suggesting that their growth and maintenance are not as sensitive to oxygen supply as other microbes (i.e., gram negative bacteria, protozoa, actinomycetes, and fungi). The findings will be used by other soil scientists and agronomists to develop strategies to maintain soil health, especially in areas that receives periodic flooding.
Technical Abstract: Redox states affect substrate availability and energy transformation, and, thus, play a crucial role in regulating soil microbial abundance, diversity, and community structure. We evaluated microbial communities in soils under oxic, intermittent, and anoxic conditions along a river floodplain continuum using fatty acid methyl ester (FAME) and 16S rRNA-based terminal-restriction fragment length polymorphism (T-RFLP) fingerprints. Subsurface soil microbial communities distinctly grouped according to flooding influence. This type of grouping, however, was not observed for the oxic soils for which flooding influence was prominent. In all the soils tested, microbial communities clustered according to soil redox state by both evaluation techniques, indicating that redox state played a dominant role regulating microbial diversity and community structure. Bacteria are dominant components of soil microbial communities, while mycorrhizal fungi composed about 12% of the microbial community in the oxic soils. Although most microorganisms, including gram-negative bacteria, fungi and actinomycetes, were more abundant in the oxic layers than in the intermittent and anoxic layers, gram-positive bacteria consisted >10% of the community in all soils tested and their abundance increased with increasing soil depth when shifting from oxic to anoxic conditions. In the anoxic soils, gram-positive bacteria composed about 16% of the total community, suggesting that their growth and maintenance were not as sensitive to oxygen supply as for other environmental microbes. In general, microorganisms were more abundant and diverse, and distributed more evenly in the oxic layers than the anoxic layers. The decrease in abundance with increasing oxygen and substrate limitation, however, was considerably more drastic than the decrease in diversity, suggesting that growth of soil microorganisms is more energy demanding than maintenance. The lower diversity in the deeper intermittent and anoxic soils was attributed primarily to changes in the redox states.