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The article discusses the highlights of mycorrhizal ecology and related sessions at the Ecological Society of America 92nd Annual Meeting held in San Jose, California, in August 2007. Researchers reported some of their work on mycorrhiza at the meeting. Shannon Schechter presented a cloning and sequencing approach to compare arbuscular mycorrhizal fungi. Researchers were also interested in using tools developed by ecologists and testing ecological theories developed for other organisms on fungi.

Release rates of recently fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ from non-exchangeable interlayer sites in 2:1 silicate minerals were determined for decomposed granite (DG) saprolites from three locations in California, USA. Recently-fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ release from the DG substrate was quantified by extracting diffused $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ with H-resin, as well as a native, annual grass Vulpia microstachys. The $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ release data varied with via the method of extraction, which included H-resin pre-treatments (Na+ or H+) and V. microstachys uptake (mycorrhizal inoculated or uninoculated). After 6 weeks (1008 h), more $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ was recovered from fixed interlayer positions by the H-resins as compared to uptake by V. microstachys. The H+ treated H-resins recovered more released $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ (≈94 mg $${\text{NH}}^{{\text{ + }}}_{{\text{4}}} - {\text{N}}\;{\text{kg}}^{1} $$ or (12%) of total fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ ) in two of the three DG samples as compared to the Na+ treated resins, (which recovered ≈70–78 mg $${\text{NH}}^{{\text{ + }}}_{{\text{4}}} - {\text{N}}\;{\text{kg}}^{{{\text{ - 1}}}} $$ (or 9–10%) of the total fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ ). The V. microstachys assimilated 8–9% of the total fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ with mycorrhizal inoculum as compared to only 2% without a mycorrhizal inoculum, over the same time period. The fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ release kinetics from the H-resin experiments were most accurately described by first order and power function models, and can be characterized as biphasic using a heterogeneous diffusion model. Uptake of both the 15N and ambient, unlabelled N from the soils was closely related to plant biomass. There was no significant difference in percent of N per unit of biomass between the control and mycorrhizal treatments. The findings presented here indicate that observed, long-term $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ release rates from DG in studies utilizing resins, may overestimate the levels of fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ made available to plants and microorganisms. Additionally, the study suggested that mycorrhizae facilitate the acquisition and plant uptake of fixed $$ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $$ , resulting in markedly increased plant biomass production. [ABSTRACT FROM AUTHOR]

• Stable isotope abundance analyses recently revealed that some European green orchids and pyroloids (Ericaceae) are partially myco-heterotrophic, exploiting mycorrhizal fungi for organic carbon and nitrogen. Here we investigate related species to assess their nutritional mode across various forest and climate types in Germany and California. • C- and N-isotope signatures of five green pyroloids, three green orchids and several obligate myco-heterotrophic species (including the putatively fully myco-heterotrophic Pyrola aphylla) were analysed to quantify the green plants’ nutrient gain from their fungal partners and to investigate the constancy of enrichment in 13C and 15N of fully myco-heterotrophic plants from diverse taxa and locations relative to neighbouring autotrophic plants. • All green pyroloid and one orchid species showed significant 15N enrichment, confirming incorporation of fungi-derived N compounds while heterotrophic C gain was detected only under low irradiance in Orthilia secunda. Pyrola aphylla had an isotope signature equivalent to those of fully myco-heterotrophic plants. • It is demonstrated that primarily N gain from mycorrhizal fungi occurred in all taxonomic groups investigated across a wide range of geographical and ecological contexts. The 13C and 15N enrichment of obligate myco-heterotrophic plants relative to accompanying autotrophic plants turned out as a fairly constant parameter. [ABSTRACT FROM AUTHOR]

On the northern California coast, mixed conifer forests occur on younger, relatively fertile terraces, whereas mesic and hydric pygmy forests occur on older, infertile, poorly drained terraces. We characterized mycorrhizal associations, ectomycorrhizal morphotypes, and colonization levels for nine plant species from three plant communities (mixed conifer, mesic pygmy, and hydric pygmy). Pinus contorta ssp. bolanderi (Parl.) Critchf. and Pinus muricata D. Don were ectomycorrhizal; all ericaceous plants formed ericoid mycorrhizas except Arctostaphylos nummularia A. Gray, which formed only arbutoid mycorrhizas. Arbuscular mycorrhizas were not observed, even on Cupressus goveniana ssp. pigmaea (Lemmon) J. Bartel. Ectomycorrhizal colonization was significantly lower in pygmy forests, while ericoid mycorrhizal colonization was significantly higher, as compared with the mixed conifer forest. Ectomycorrhizal and ericoid mycorrhizal colonization was greater on hummocks than in swales at hydric pygmy sites. Thirteen distinct ectomycorrhizal and arbutoid mycorrhizal morphotypes were observed: eight only on Pinus spp. and two only on A. nummularia. Two morphotypes were found only in mixed conifer, and eight were found only in pygmy communities. Distribution of morphotypes may reveal habitat and (or) host adaptation by ectomycorrhizal fungi.Key words: ectomycorrhizal morphotypes, ericoid mycorrhizas, pygmy forest, Ericaceae, mycorrhizal colonization, low-fertility soils.Les forêts conifériennes mixtes se retrouvent sur des terrasses plus jeunes et relativement fertiles, alors que les forêts naines occupent des terrasses infertiles plus âgées et mal drainées. Les auteurs ont caractérisé les associations mycorhiziennes, les morphotypes ectomycorhiziens et les degrés de colonisation chez neuf espèces de plantes appartenant à trois communautés végétales, forêt coniférienne mixte, forêt naine mésique et forêt naine hydrique, localisées sur des terrasses marines de la côte ouest de la Californie. Le Pinus contorta spp. bolanderi (Parl.) Critchf. et le Pinus muricata D. Don forment des ectomycorhizes; toutes les plantes éricacées forment des mycorhizes éricoïdes, sauf l'Arctostaphylos ummularia A. Gray qui forme seulement des mycorhizes arbutoïdes. Aucune mycorhize arbusculaire n'a été observée, même chez le Cupressus goveniana spp. pigmaea (Lemmon) J. Bartel. La colonisation ectomycorhizienne est significativement plus faible dans les forêts naines, alors que la colonisation éricoïde y est significativement plus élevée, comparativement à la forêt coniférienne mixte. Les colonisations ectomycorhiziennes et éricoïdes sont plus abondantes sur les hummocks. On a observé 13 morphotypes d' ectomycorhizes et de mycorhizes éricoïdes, 8 seulement sur les pins, et 2 seulement sur l'A. nummularia. Deux morphotypes ne se retrouvent que dans la forêt coniférienne mixte, et 8 ne se retrouvent que dans les communautés forestières naines. La distribution des morphotypes peut révéler l'habitat et (ou) l'adaptation par les champignons ectomycorhiziens.Mots clés : morphotypes ectomycorhiziens, mycorhizes éricoïdes, forêts naines, Ericaceae, colonisation mycorhizienne, sols peu fertiles.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Reports on research on effective recipe for guarding strawberry fields in California from weeds and diseases. Description of the compositions of experimental compost; Details on the effect of mycorrhizae.