Decreasing prevalence of rhizosphere IAA producing and seedling root growth promoting bacteria with barley development irrespective of protozoan grazing regime
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Barley was grown in soil with either bacteria and a mixed protozoan community (Mixed protozoa) or bacteria and a single vahlkampfiid amoebal species (Single amoeba). We assessed the influence of plant age (day 29, 43 and 57 after sowing) on two aspects of rhizosphere bacterial functioning: (1) the proportion of indole-3-acetic acid (IAA) producing bacteria and (2) the effect of mixed rhizosphere bacterial assemblages on barley seedling root growth in an agar based assay. The proportion of IAA producers was significantly lower at day 57 than at day 29 and 43, and mixed bacterial assemblages extracted from rhizospheres of 29 days old plants were significantly less harmful to seedling growth than bacterial assemblages from older plants. Hence both assays indicated that bacterial communities from rhizospheres of older plants were less beneficial for root growth than bacterial communities from younger plants. Genetic fingerprinting of rhizosphere bacterial communities was compared by use of length heterogeneity polymerase chain reaction (LH-PCR). This analysis showed a clear succession from the inoculum bacterial community with a rather low diversity to a community with much higher diversity at day 29. However, diversity did not change after day 29, and no relationship between protozoan treatment nor plant age and genetic fingerprinting was found.
KeywordsBacterial metabolites Flagellates LH-PCR Plant deleterious bacteria PGPR
We thank Flemming Ekelund for assistance on protozoan identification and Anders Priemé and Karin Vestberg (Section of Microbiology, University of Copenhagen) for running the LH-PCR samples.
- Åström B, Gustafsson A, Gerhardson B (1993) Characteristics of a plant deleterious rhizosphere pseudomonad and its inhibitory metabolite(s). J Appl Bacteriol 74:20–28Google Scholar
- Campbell R, Greaves MP (1990) Anatomy and community structure of the rhizosphere. In: Lynch JM (ed) The Rhizosphere. John Wiley & Sons, Chichester, pp 11–34Google Scholar
- Chakrabarti T, Doy CH, Subrahmanyam NC (1978) The analysis of barley genomes. I: The problem that the DNA of bacteria may contribute to the DNA in extracts of barley tissues derived from germinated seeds. Barley Genetics Newsletter 8:25–28Google Scholar
- Curl EA, Truelove B (1986) The rhizosphere. Springer-Verlag, BerlinGoogle Scholar
- Darbyshire JF, Wheatley RE, Greaves MP, Inkson RHE (1974) A rapid micromethod for estimating bacterial and protozoan populations in soil. Rev Écol Biol Sol 11:465–475Google Scholar
- Frankenberger WT, Arshad M (1995) Phytohormones in soils. Microbial production and function. Marcel Dekker, Inc., New YorkGoogle Scholar
- Griffiths BS, Bonkowski M, Dobson G, Caul S (1999) Changes in soil microbial community structure in the presence of microbial-feeding nematodes and protozoa. Pedobiologia 43:297–304Google Scholar
- Hankes LV, Riesen WH, Henderson LM, Elvehjem CA (1948) Liberation of amino acids from raw and heated casein by acid and enzyme hydrolysis. J Biol Chem 176:467–476Google Scholar
- Magurran AE (2003) Measuring biological diversity. Blackwell Science Ltd, MaldenGoogle Scholar
- Page FC (1988) A new key to freshwater and soil gymnamoebae. Freshwater Biological Association, AmblesideGoogle Scholar
- Rønn R, Ekelund F, Christensen S (1995) Optimizing soil extract and broth media for MPN-enumeration of naked amobae and heterotrophic flagellates in soil. Pedobiologia 39:10–19Google Scholar