Summary
Cucumber was grown in a partially sterilized sand-soil mixture with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum or left uninoculated. Fresh soil extract was places in polyvinyl chloride tubes without propagules of mycorrhizal fungi. Root tips and root segments with adhering soil, bulk soil, and soil from unplanted tubes were sampled after 4 weeks. Samples were labelled with [3H]-thymidine and bacteria in different size classes were measured after staining by acridine orange. The presence of VAM decreased the rate of bacterial DNA synthesis, decreased the bacterial biomass, and changed the spatial pattern of bacterial growth compared to non-mycorrhizal cucumbers. The [3H]-thymidine incorporation was significantly higher on root tips in the top of tubes, and on root segments and bulk soil in the center of tubes on non-mycorrhizal plants compared to mycorrhizal plants. At the bottom of the tubes, the [3H]-thymidine incorporation was significantly higher on root tips of mycorrhizal plants. Correspondingly, the bacterial biovolumes of rods with dimension 0.28–0.40×1.1–1.6 μm, from the bulk soil in the center of tubes and from root segments in the center and top of tubes, and of cocci with a diameter of 0.55–0.78 μm in the bulk soil in the center of tubes, were significantly reduced by VAM fungi. The extremely high bacterial biomass (1–7 mg C g-1 dry weight soil) was significant reduced by mycorrhizal colonization on root segments and in bulk soil. The incorporation of [3H]-thymidine was around one order of magnitude lower compared to other rhizosphere measurements, probably because pseudomonads that did not incorporate [3H]-thymidine dominated the bacterial population. The VAM probably decreased the amount of plant root-derived organic matter available for bacterial growth, and increased bacterial spatial variability by competition. Thus VAM plants seem to be better adapted to compete with the saprophytic soil microflora for common nutrients, e.g., N and P, compared to non-mycorrhizal plants.
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References
Ames RN, Reid CPP, Ingham ER (1984) Rhizosphere bacterial population responses to root colonization by a vesicular-arbuscular mycorrhizal fungus. New Phytol 96:555–563
Bååth E (1990) Thymidine incorporation into soil bacteria. Soil Biol Biochem 22:803–810
Bååth E, Johnasson T (1990) Measurement of bacterial growth rates on the rhizoplane using 3H-thymidine incorporation into DNA. Plant and Soil 126:113–139
Babuik LA, Paul EA (1970) The use of fluorescein isothiocyanate in the determination of the bacterial biomass of grassland soil. Can J Microbiol 16:57–62
Bakken LR (1982) The turnover of C and N in cultivated soil at different fertilizer levels. Ph D thesis. Agric Univ Norway
Barber DA, Martin JK (1976) The release of organic substances by cereal roots into soil. New Phytol 76:69–80
Bowen GD, Rovira AD (1976) Microbial colonization of plant roots. Annu Rev Phytopathol 14:121–144
Christensen H (1991 a) Conversion factors relating thymidine uptake to growth rate with rhizosphere bacteria. In: Keisler DL, Gregan PB (eds) The rhizosphere and plant growth. Kluwer Academic Publishers, Dordrecht, pp 99–102
Christensen H (1991 b) Growth rate of rhizosphere bacteria as measured by the thymidine method. In: Keisler DL, Gregan PB (eds) The rhizosphere and plant growth. Kluwer Academic Publishers, Dordrecht, p 105
Christensen H, Funck-Jensen D, Kjøller A (1989) Growth rate of rhizosphere bacteria measured directly by the tritiated thymidine incorporation technique. Soil Biol Biochem 21:113–117
Christensen H, Griffiths B, Christensen S (1992) Bacterial incorporation of tritiated thymidine and populations of bacteriophagous fauna in the rhizosphere of wheat. Soil Biol Biochem 24:703–709
Davis CL (1989) Uptake and incorporation of thymidine by bacterial isolates from an upwelling environment. Appl Environ Microbiol 55:1267–1272
Güde H (1984) Test for validity of different radioisotopes activity measurements by microbial pure and mixed cultures. Arch Hydrobiol Beih Ergeb Limnol 19:257–266
Hobbie JE, Daley RJ, Jasper S (1977) Use of nuclepore filters for counting bacteria by fluorescence microscopy. Appl Environ Microbiol 33:1225–1228
Jakobsen I, Rosendahl L (1990) Carbon flow into soil and external hyphae from roots of mycorrhizal cucumber plants. New Phytol 115:77–83
Jenkinson DS, Powlson DS, Wedderburn RWM (1976) The effects of biocidal treatments on metabolism in soil: III. The relationship between soil biovolume, measured by optical microscopy, and the flush of decomposition caused by fumigation. Soil Biol Biochem 8:189–202
Linderman RG (1988) Mycorrhizal interactions with the rhizosphere microflora. Phytopathology 78:366–371
Lynch JM, Panting LM (1980) Variations in the size of the soil biomass. Soil Biol Biochem 12:547–550
Lynch JM, Whipps JM (1990) Substrate flow in the rhizosphere. Plant and Soil 129:1–10
Meyer JR, Linderman RG (1986) Selective influence on populations of rhizosphere or rhizosplane bacteria and actinomycetes by mycorrhizas formed by Glomus fasciculatum. Soil Biol Biochem 18:191–196
Paulitz TC, Linderman RG (1989) Interactions between fluorescent pseudomonads and VA-mycorrhizal fungi. New Phytol 113:37–45
Pietr SJ, Kempa R (1989) Cucumber rhizosphere pseudomonads as antagonists of Fusarium. In: Vancura V, Kunc F (eds) Interrelationships between microorganisms and plants in soil. Academia, Praha, pp 411–417
Pollard PC, Moriarty DJW (1984) Validity of the tritiated thymidine method for estimating bacterial growth rates: Measurements of isotope dilution during DNA synthesis. Appl Environ Microbiol 48:1076–1083
Rovira AD, Sands DC (1971) Fluorescent pseudomonads — a residual component in the soil microflora? J Appl Bacteriol 34:253–259
Sauerbeck DR, Johnen BG (1977) Root formation and decomposition during plant growth. In: Soil organic matter studies, vol 1. Int Atomic Energy Agency, Vienna, pp 141–148
Schwab SM, Menge JA, Leonard RT (1983) Quantitative and qualitative effects of phosphorus on extracts and exudates of sudangrass roots in relation to vesicular-arbuscular mycorrhiza formation. Plant Physiol 73:761–765
Secilia J, Bagyaraj DJ (1987) Bacteria and actinomycetes associated with pot cultures of vesicular-arbuscular mycorrhizas. Can J Microbiol 33:1069–1073
Simon M, Azam F (1989) Protein content and protein synthesis rates of planktonic marine bacteria. Mar Ecol Prog Ser 51:201–213
Stille B (1938) Untersuchungen über die Bedeutung der Rhizosphäre. Arch Mikrobiol 9:477–485
West AW, Sparling GP, Grant WD (1987) Relationship between mycelial and bacterial populations in stored, air-dried and glucose-amended arable and grassland soil. Soil Biol Biochem 19:599–605
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Christensen, H., Jakobsen, I. Reduction of bacterial growth by a vesicular-arbuscular mycorrhizal fungus in the rhizosphere of cucumber (Cucumis sativus L.). Biol Fertil Soils 15, 253–258 (1993). https://doi.org/10.1007/BF00337209
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DOI: https://doi.org/10.1007/BF00337209