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Journal Article

Response of Vulpia Ciliata ssp. Ambigua to Removal of Mycorrhizal Infection and to Phosphate Application Under Natural Conditions

H. M. West, A. H. Fitter and A. R. Watkinson
Journal of Ecology
Vol. 81, No. 2 (Jun., 1993), pp. 351-358
DOI: 10.2307/2261505
Stable URL: http://www.jstor.org/stable/2261505
Page Count: 8
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Response of Vulpia Ciliata ssp. Ambigua to Removal of Mycorrhizal Infection and to Phosphate Application Under Natural Conditions
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Abstract

1. We have conducted a series of factorial experiments involving the application of the fungicide benomyl to reduce mycorrhizal infection, and of phosphate, to ascertain whether mycorrhizal fungi contribute to fitness in the winter annual grass Vulpia ciliata ssp. ambigua and whether any such contribution can be ascribed to increased P uptake. 2. Experiments were set up at four sites in East Anglia (UK) where the grass grows with large differences in the natural intensity of mycorrhizal infection. At one site, the factorial experiment was nested within an irrigation treatment. In addition, we performed experiments to test the yield response of V. ciliata to added P. 3. Plant response to P was slight: a small stimulus at very low addition rates and a depression at high rates. Arbuscular mycorrhizal infection was well controlled by benomyl addition, but fecundity in this annual grass was scarcely affected either by P or benomyl application. Only at one of the four sites did benomyl application alter fecundity: it increased both number of seeds per plant and mean seed mass. 4. Percentage infection was a positive covariate of plant performance at two sites, unrelated at one, and a negative covariate at one, suggesting that infection can be beneficial, neutral or deleterious depending on conditions. 5. It seems unlikely that any benefits derived from increased P uptake: across all sites and treatments, P inflow was unrelated to infection, and in control plots the relationship was negative, the most infected plants having the lowest inflows. Benefit may have been protection from pathogens: at one site where Fusarium oxysporum had previously been shown to be abundant, no effect of benomyl could be detected, as would be expected if both the mycorrhizal and the pathogenic fungus were eliminated. 6. These data show that benefits of arbuscular mycorrhizal infection may be dependent on local conditions and may be due to other effects than increased P uptake.

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