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Negative Associations among VA-Mycorrhizal Fungi and Some Ectomycorrhizal Fungi Inhabiting the Same Root System
D. Jean Lodge and Thomas R. Wentworth
Vol. 57, No. 3 (Apr., 1990), pp. 347-356
Stable URL: http://www.jstor.org/stable/3565964
Page Count: 10
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Earlier surveys of Populus deltoides Bartr. and Salix nigra ×? had suggested displacement of VA-mycorrhizal fungi by ectomycorrhizal fungi from the middle of soil moisture gradients. Succession from VA- to ectomycorrhizal associations had also been observed previously in several plant species. Data were therefore analyzed for evidence of negative interactions among VA- and ectomycorrhizal fungi inhabiting the same root system. Fine roots (< 2 mm diameter) were sampled from natural populations of cottonwood growing in the eastern USA, and from two field-infected cottonwood clones grown under uniform soil conditions in North Carolina. Percentages of non-mycorrhizal, VA-mycorrhizal, ectomycorrhizal, and dually colonized root lengths were determined for terminal (most distal branches of the fine roots) and non-terminal roots in each sampling unit. Dual mycorrhizae (VA- and ectomycorrhizal fungi in the same cross section) in terminal roots of almost all Populus sampling units were significantly lower than expected from a random assortment model. Negative association with VA-mycorrhizal fungi varied among ectomycorrhizal morpho-types. The degree of negative association among mycorrhizal fungi was determined using a new statistical test based on linear regression. High levels of ectomycorrhizal colonization were related to depression of VA-mycorrhizal colonization in terminal as compared with non-terminal roots within the same sampling unit. Although these data are not conclusive, they suggest that ectomycorrhizal fungi might displace VA-mycorrhizal fungi from roots of VA-/ectomycorrhizal hosts.
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