Arbuscular mycorrhizal fungi from three genera induce two-phase plant growth responses on a high P-fixing soil |
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Authors: | Peter F Schweiger Alan D Robson N Jim Barrow Lyn K Abbott |
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Institution: | 1. School of Earth and Geographical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia 3. Institute of Soil Science, University of Natural Resources and Applied Life Sciences, Peter Jordan Stra?e 82, 1190, Vienna, Austria 4. The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia 2. 22 Townsend Dale, Mt Claremont, WA, 6010, Australia
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Abstract: | Plant growth enhancing effects of arbuscular mycorrhizal (AM) fungi are suitably quantified by comparisons of mycorrhizal
and non-mycorrhizal plant growth responses to added phosphorus (P). The ratio between the amounts of added P required for
the same yield of mycorrhizal and non-mycorrhizal plants is termed the relative effectiveness of the mycorrhiza. Variation
in this relative effectiveness was examined for subterranean clover grown on a high P-fixing soil. Plants were either left
non-mycorrhizal or inoculated with one of three AM fungal species with well-characterised differences in external hyphal spread.
With no P added, plants from all treatments produced <10% of their maximum growth achieved at non-limiting P supply. The growth
response of non-mycorrhizal plants was markedly sigmoid. Mycorrhizal growth responses were not sigmoid but their shape was
two-phased. The first phase was an asymptotic approach to 25–30% of maximum growth, followed by a second asymptotic rise to
maximum growth. Growth effects of Glomus invermaium and Acaulospora laevis were quite similar. Plants in these treatments produced up to four times greater shoot dry biomass than non-mycorrhizal plants.
Scutellospora calospora was less effective. The relative effectiveness of AM fungi varied with the level of P application. This is expected to apply
to all soils on which a sigmoid response is obtained for growth of non-mycorrhizal plants. In a simple approximation the relative
effectiveness was calculated to range from 1.46 to 15.57. Shoot P contents were increased by up to 25 times by A. laevis, significantly more than by the other two fungi. The further mycelial spread of this fungus is thought to have contributed
to its relatively greater effect on plant P content. |
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Keywords: | Acaulospora Glomus Mitscherlich Relative effectiveness Response curve Scutellospora |
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