Douglas-fir ectomycorrhizae in 40- and 400-year-old stands: mycobiont availability to late successional western hemlock.

We investigated ectomycorrhizal (EM) fungi in forest stands containing both early successional Douglas-fir and late successional western hemlock at two points in the typical stand development by identifying EM fungi from roots of Douglas-fir and western hemlock in mixed stands. In an early seral stage forest, EM roots of western hemlock seedlings and intermingling 40-year-old Douglas-fir were sampled. In a late seral stage forest, EM roots of trees of both species were sampled in a 400-year-old stand. We use molecular approaches to identify the symbionts from field samples in this descriptive study. In the early seral stage study, >95% of the western hemlock root tips by biomass were colonized by fungi also colonizing Douglas-fir roots. This result supports the prediction that western hemlock can associate with fungi in Douglas-fir EM networks. In the same study, fungi specific to Douglas-fir colonized 14% of its EM root tips. In the late seral stage study, 14% of the western hemlock root tips were colonized by fungi also observed in association with Douglas-fir, a result strongly influenced by sampling issues and likely represents a conservative estimate of multiple host fungi in this old growth setting. Fungi specific to Douglas-fir colonized 25% of its root tip biomass in the old growth study, in tight coralloid clusters within five of the 24 soil samples. The trends revealed in this study corroborate earlier studies suggesting a predominance of multiple host fungi in mixed communities of EM plants. The role of host-specific fungi in these stands remains unclear.

Pezizalean mycorrhizas and sporocarps in ponderosa pine (Pinus ponderosa) after prescribed fires in eastern Oregon, USA.

Post-fire Pezizales fruit commonly in many forest types after fire. The objectives of this study were to determine which Pezizales appeared as sporocarps after a prescribed fire in the Blue Mountains of eastern Oregon, and whether species of Pezizales formed mycorrhizas on ponderosa pine, whether or not they were detected from sporocarps. Forty-two sporocarp collections in five genera (Anthracobia, Morchella, Peziza, Scutellinia, Tricharina) of post-fire Pezizales produced ten restriction fragment length polymorphism (RFLP) types. We found no root tips colonized by species of post-fire Pezizales fruiting at our site. However, 15% (6/39) of the RFLP types obtained from mycorrhizal roots within 32 soil cores were ascomycetes. Phylogenetic analyses of the 18S nuclear ribosomal DNA gene indicated that four of the six RFLP types clustered with two genera of the Pezizales, Wilcoxina and Geopora. Subsequent analyses indicated that two of these mycobionts were probably Wilcoxina rehmii, one Geopora cooperi, and one Geopora sp. The identities of two types were not successfully determined with PCR-based methods. Results contribute knowledge about the above- and below-ground ascomycete community in a ponderosa pine forest after a low intensity fire.

The molecular revolution in ectomycorrhizal ecology: peeking into the black-box.

Molecular tools have now been applied for the past 5 years to dissect ectomycorrhizal (EM) community structure, and they have propelled a resurgence in interest in the field. Results from these studies have revealed that: (i) EM communities are impressively diverse and are patchily distributed at a fine scale below ground; (ii) there is a poor correspondence between fungi that appear dominant as sporocarps vs. those that appear dominant on roots; (iii) members of Russulaceae, Thelephoraceae, and/or non-thelephoroid resupinates are among the most abundant EM taxa in ecosystems sampled to date; (iv) dissimilar plants are associated with many of the same EM species when their roots intermingle--this occurs on a small enough spatial scale that fungal individuals are likely to be shared by dissimilar plants; and (v) mycoheterotrophic plants have highly specific fungal associations. Although, these results have been impressive, they have been tempered by sampling difficulties and limited by the taxonomic resolution of restriction fragment length polymorphism methods. Minor modifications of the sampling schemes, and more use of direct sequencing, has the potential to solve these problems. Use of additional methods, such as in situ hybridization to ribosomal RNA or hybridization coupled to microarrays, are necessary to open up the analysis of the mycelial component of community structure.

The occurrence of radioactivity in public water supplies in the United States.

Examination of the collected data for radionuclide concentration measurements in public water supplies in the United States show more than 51,000 measurements for gross alpha-particle activity and/or Ra, 89,900 measurements for U, and 9,000 measurements for Rn. These measurements were made as part of national and state surveys of radionuclide concentrations in utility water supplies for Ra and Rn; and the National Uranium Resource Evolution (NURE) survey for U which included non-utility water supplies. Surface water has low values for Ra and Rn but levels comparable to ground water for U. Separate isotope measurements were not taken for much of the Ra and U data. Because 226Ra to 228Ra ratios and 238U to 234U ratios are not fixed in water, further measurements are needed to establish the specific isotopic concentrations by region. Analysis of the state average values in geological provinces shows the highest provincial areas for Ra are the Upper Coastal Plain, the glaciated Central Platform, and the Colorado plateau. For U, the highest areas are the Colorado plateau, the West Central Platform, and the Rocky Mountains. For Rn, the highest provinces are New England and the Appalachian Highlands-Piedmont. Regional hydrogeological and geochemical models are suggested for guiding the formulation of regional standards and monitoring strategies. Utility supplies serving small populations have the highest concentration for each radionuclide and have the lowest fraction of samples measured, which shows a need for further measurements of these small population water supplies. Risk estimates for the average concentration of Ra in utility ground water give about 941 fatal cancers per 70.7-yr lifetime in the United States. Risk estimates for the average concentration of U in utility surface and ground water give about 105 fatal cancers per 70.7-yr lifetime in the United States. Using 1 pCi/liter in air for 10,000 pCi/l in water, the Rn in utility water risk estimate is for 4,400-22,000 fatal cancers per 70.7-yr lifetime in the United States.