Mycorrhizal responsiveness of Thuja, Calocedrus, Sequoia, and Sequoiadendron species of western North America

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Abstract
Four western conifers inoculated or not inoculated with three species of vesicular–arbuscular mycorrhizal fungi were grown in pasteurized soil and maintained at 11 or 43 ppm phosphorus. Compared with controls, vesicular–arbuscular mycorrhizal colonization increased biomass more of younger than older seedlings. In young seedlings, species with large seeds responded less to phosphate addition or vesicular–arbuscular mycorrhizal colonization than smaller seeded species. Vesicular–arbuscular mycorrhizal seedlings with low phosphorus were always larger than noninoculated low phosphorus controls and comparable in size or larger than nonmycorrhizal controls at moderate phosphorus. Vesicular–arbuscular mycorrhizal plants produced from 100 to 2000% more biomass than noninoculated plants at low phosphorus, and from equality to 500% at moderate phosphorus. Vesicular–arbuscular mycorrhizal fungal species did not differ in plant growth enhancement or root colonization at any seedling age or phosphorus fertility examined. Tree species' responsiveness ranged as follows: Thujaplicata > Sequoiasempervirens > Calocedrusdecurrens > Sequoiadendrongiganteum. Vesicular–arbuscular mycorrhizal fungi enhanced seedling uniformity and size in all the tree species.