Distribution of spore-positive and spore-negative nodules ofAlnus incana ssp.rugosa in Maine,USA |
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Authors: | Rosanne M Holman Christa R Schwintzer |
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Institution: | (1) Department of Botany and Plant Pathology, University of Maine, 04469 Orono, ME, USA |
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Abstract: | The distribution of spore-positive (sp+) and spore-negative (sp−) root nodules ofAlnus incana ssp.rugosa (DuRoi) Clausen (speckled alder) was examined at 29 sites with a wide range of environmental conditions in Maine, USA. These
included: pH 3.4 to 7.0, soil texture ranging from coarse gravel to clay to organic soils, elevation from 3 to 591 m and latitude
43 to 47°N. Habitat types included disturbed areas, streamsides, swamps and old fields.
Sp (−) nodules were substantially more common, making up 76% of all nodules, whereas only 24% were sp (+). Sp (−) nodules
often occurred in pure stands and predominated at disturbed sites with mineral soils at the surface and in old fields and
swamps with pH>4.0 Sp (+) nodules were nearly always found in mixture with sp (−) nodules. They occurred primarily at streamside
and lakeshore sites where they made up 40% of the nodules and at sites with pH<4.0 regardless of habitat type. It is suggested
that sp (−) strains ofFrankia may be maintained at a site by saprophytic growth in soil and thus nodulate newly established hosts, whereas sp (+) strains
may be maintained primarily by spore production within nodules and thus depend on extended presence of the host. |
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Keywords: | actinorhizal plants Alnus incana ssp rugosa Frankia nitrogen fixation root nodules spore-negative spore-positive |
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