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In the Arctic and subarctic, climate change is causing reduced snowpack extent and earlier snowmelt. Shallower snowpack decreases the thermal insulation of underlying soil and results in more freeze-thaw conditions reflective of dynamic air temperatures. The aim of this study was to determine the effect of alternative temperature regimes on overall microbial community structure and rhizosphere recruitment across representatives of three subarctic plant functional groups. We hypothesized that temperature regime would influence rhizosphere community structure more than plant type. Planted microcosms were established using a tree, forb, grass, or no plant control and subjected to either freeze-thaw cycling or static subzero temperatures. Our results showed rhizosphere communities exhibited reduced diversity compared to bulk soils, and were influenced by temperature conditions and to a lesser extent plant type. We found that plants have a core microbiome that is persistent under different winter temperature scenarios but also have temperature regime-specific rhizosphere microbes. Freeze-thaw cycling resulted in greater community shifts from the pre-incubation soils when compared to constant subzero temperature. This finding suggests that wintertime snowpack conditions may be a significant factor for plant-microbe interactions upon spring thaw. [ABSTRACT FROM AUTHOR]

Many ectomycorrhizal fungi (EMF) are generalists, but most plant genera that form ectomycorrhizas have at least some fungal partners that are specific to that host genus. Because shared mycorrhizal fungi mediate plant community interactions, host preference has implications for plant succession and competition. We studied the EMF of oaks (Quercus spp.) and pines (Pinus spp.) in a forest in northern Florida, USA, focusing on symbionts shared with longleaf pine (Pinus palustris Mill.). Longleaf pine is an important species in the southeastern USA, both for timber plantations and for restoring savanna and woodland habitat. However, we found no research on the composition of naturally occurring EMF on longleaf pine roots. A lower proportion of EMF operational taxonomic units (OTUs) were found colonizing both oaks and pines than expected, providing evidence of host preference within the community. Although most EMF were detected only on either oaks or pines, the OTUs found on both tended to be frequently occurring and abundant. Cenococcum OTUs were found to be significantly associated with oaks, an unexpected finding as this genus is widespread, with a broad host range. These results suggest that host preference of EMF may structure EMF communities and therefore influence ecosystem effects of mycorrhizal networks. Key words: host specificity, host preference, ectomycorrhizal fungi, mycorrhizal networks, Pinus palustris. Plusieurs champignons ectomycorhiziens (CEM) sont des generalistes mais la plupart des genres de vegetaux qui forment des ectomycorhizes comptent au moins un certain nombre de partenaires fongiques specifiques a un genre hote donne. Parce que les champignons mycorhiziens partages sont a la base des interactions dans les communautes vegetales, la preference pour un hote a des repercussions sur la competition et la succession chez les plantes. Nous avons etudie les CEM des chenes (Quercus spp.) et des pins (Pinus spp.) dans une foret du nord de la Floride, aux Etats-Unis. Nous avons mis l'accent sur les symbiotes partages avec le pin des marais (Pinus palustris Mill.). Le pin des marais est une espece importante dans le sud-est des Etats-Unis pour la production de bois en plantation et la restauration des savanes et des habitats boises. Cependant, nous n'avons trouve aucune etude portant sur la composition des CEM naturellement presents sur les racines du pin des marais. La proportion d'unites taxonomiques operationnelles (OTU) de CEM qui colonisaient autant les chenes que les pins etait plus faible que ce qui avait ete anticipe, ce qui constitue un indice d'hote preferentiel au sein de la communaute. Bien que la plupart des CEM aient ete detectes exclusivement soit sur les chenes, soit sur les pins, les OTU trouvees sur les deux avaient tendance a etre presentes frequemment et de nombreuses OTU de Cenococcum etaient associees de facon significative aux chenes, un resultat inattendu etant donne que ce genre est largement repandu et possede une vaste gamme d'hotes. Ces resultats indiquent que la preference des CEM pour un hote peut structurer les communautes de CEM et par consequent influencer les effets des reseaux mycorhiziens sur l'ecosysteme. [Traduit par la Redaction] Mots-cles : specificite de l'hote, preference pour un hote, champignons ectomycorhiziens, reseaux mycorhiziens, Pinus palustris., Introduction Specificity in species' interactions is important in understanding community ecology, coevolution, and even predicting extinction risk (Molina et al. 1992; Bruns et al. 2002; Thompson 2009; Devictor et al. [...]

Permafrost thawing could increase soil contaminant mobilization in the environment. Our objective was to quantify metal accumulation capacities for plant species and functional groups common to Alaskan military training ranges where elevated soil metal concentrations were likely to occur. Plant species across multiple military training range sites were collected. Metal content in shoots and roots was compared to soil metal concentrations to calculate bioconcentration and translocation factors. On average, grasses accumulated greater concentrations of Cr, Cu, Ni, Pb, Sb, and Zn relative to forbs or shrubs, and bioconcentrated greater concentrations of Ni and Pb. Shrubs bioconcentrated greater concentrations of Sb. Translocation to shoots was greatest among the forbs. Three native plants were identified as candidate species for use in metal phytostabilization applications. Elymus macrourus, a grass, bioconcentrated substantial concentrations of Cu, Pb, and Zn in roots with low translocation to shoots. Elaeagnus commutata, a shrub, bioconcentrated the greatest amounts of Sb, Ni, and Cr, with a low translocation factor. Solidago decumbens bioconcentrated the greatest amount of Sb among the forbs and translocated the least amount of metals. A combination of forb, shrub, and grass will likely enhance phytostabilization of heavy metals in interior Alaska soils through increased functional group diversity. [ABSTRACT FROM AUTHOR]