Aggregation of a Silty Clay Loam Soil by Mycorrhizal Onion Roots

Thomas, Richard S.; Dakessian, S.; Ames, R. N.; Brown, Milford S.; Bethlenfalvay, Gábor J.

doi:10.2136/sssaj1986.03615995005000060023x

Cited by 60 publications

(8 citation statements)

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“…1) and tbe sterile treatment. In agreement witb assumptions of Reid &Goss (1981) and Thomas et al (1986), it is therefore more likely that root exudates are responsible either directly, or indirectly via microbial metabolites, for tbe observed soil aggregation in the rbizosphere of non-mycorrhizal plants.…”

Section: Resultssupporting

confidence: 70%

Effect of a vesicular–arbuscular mycorrhizal fungus and rhizosphere micro‐organisms on manganese reduction in the rhizosphere and manganese concentrations in maize (Zea mays L.)

1991

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SUMMARYMaize {Zea mays L. cv. Tau) plants were grown in a calcareous soil for six weeks in pots having separate compartments for growth of roots and vesicular-arbuscular (VA) mycorrhizal fungal hyphae. Soil was sterilized and either left non-inoculated (sterile treatment), or was inoculated with rhizosphere micro-organisms only (MO -VA) or with rhizosphere micro-organisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe (MO-I-VA)]. Concentrations of Mn in roots and shoots, as well as exchangeable Mn in rhizosphere soil, decreased in the order MO -VA > MO-t-V.-^ > sterile treatment. In all treatments, the concentration of exchangeable Mn was lower in the rhizosphere soil (0-5 mm distance from the root surface) thati in the bulk soil (5-15 or 15-25 mm distance from the root surface). In the rhizosphere soil, the total microbial population was sitnilar in mycorrhizal (MO-l-VA) and non-mycorrhizal (MO -VA) treatments, but the proportion of Fe-or Mti-reducers was 20-to 30-fold higher in the non-mycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbiai populations upon root infection with the mycorrhizal fungi. The Mn^'''-reducing potential (net balance between reduction and oxidation) in the rhizosphere soil was also distinctly lower in mycorrhizal treattnent compared to non-mycorrhizal tt-eatment.In the sterile treatment, low Mn*'^ -reducing potential and correspondingly low concentration of exchangeable Mn in soil, compared to the other treatments, indicates the importance of micro-organisms in Mn reduction in soil and acquisition of Mn by plants. Therefore, the lower Mn concentrations in mycorrhizal plants are most probably caused by a shift in composition and activity of rhizosphere micro-organisms. As a side effect of the treatments, improved soil aggregation, as indicated by soil adhering to the nylon net (facing hyphal compartments) after platit harvest, occurred in non-mycorrhizal and sterile treatments but not in the mycorrhizal treatment.

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Section: Resultssupporting

confidence: 70%

Effect of a vesicular–arbuscular mycorrhizal fungus and rhizosphere micro‐organisms on manganese reduction in the rhizosphere and manganese concentrations in maize (Zea mays L.)

1991

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“…Nevertheless, C losses as exudates, respiration, or other purposes need to be considered (Koide and EIliott, 1989). Root losses of C may also benefit soil properties since these C sources have been shown to enhance soil aggregation (Thomas et al, 1986). In the absence of such a compensation, plant dry matter losses may occur.…”

Section: Resultsmentioning

confidence: 99%

Benefit and cost analysis and phosphorus efficiency of VA mycorrhizal fungi colonizations with sorghum (Sorghum bicolor) genotypes grown at varied phosphorus levels

et al. 1990

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Sorghum [Sorghum bicolor (L.) Moench] was grown in a greenhouse in a low P (3.6mgkg -1) soil (Typic Argiudolls) inoculated with the vesicular-arbuscular mycorrhizal fungi (VMAF) Glomus fasciculatum and P added at 0, 12.5, 25.0, and 37.5 mgkg -1 soil to determine the effects of VAMF-root associations on plant growth, benefit and cost analysis, and P efficiency (dry matter produced/unit P absorbed). Root colonization with VAMF and shoot growth enhancements decreased with increased soil P applications. Mycorrhizal plants were less P efficient than nonmycorrhizal plants. Shoot dry matter differences between mycorrhizal and nonmycorrhizal plants were considered the benefit derived by plants from VAMF-root associations. Shoot dry matter differences between mycorrhizal and nonmycorrhizal plants with similar P concentrations were considered the costs paid by plants for VAMF-root associations. Values of benefit and cost analysis for VAMF-root associations were highest when soil P was lowest and decreased with increasing P applications. Genotypic differences for calculated costs were pronounced, but not benefits. Benefit and cost analysis may be helpful to evaluate host plant genotypes and VAMF species to optimize efficiencies of VAMF symbiosis in different soil environments.

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“…A number of studies have correlated the presence of mycorrhizas with increased water stable macroaggregates , Thomas et al 1986, Miller and Jastrow 1990) though the effects of the fungus are difficult to dissociate from those of the root. Thomas et al (1993) used split-root plants growing in four-chambered pots in a silty clay loam soil and compared water stable soil aggregates in soils containing all combinations (presence/absence) of roots and extraradical AM fungus hyphae.…”

Section: Effect Of Am Fungi On Soil Structurementioning

confidence: 99%