Photoperiod and Soil Munition Constituent Effects on Phytoaccumulation and Rhizosphere Interactions in Boreal Vegetation

Permafrost thaw is expected to alter biogeochemistry and hydrology, potentially increasing the mobility of soil constituents. Northern latitude boreal forests where permafrost thaw is occurring also experience extreme changes in day length during the growing season. As the effects of photoperiod on plant uptake of soil constituents or interactions with the rhizosphere are unknown, our objective was to determine these interactions with three plant species from different functional groups. A tree, forb, and grass common to military training ranges in this region were grown in soil spiked with or without lead, antimony, or 2,4-dinitrotoluene and grown under 16, 20, or 24 h of light. Plant biomass, soil constituent uptake, and rhizosphere bacterial communities were compared between treatments. Photoperiod had no effect on plant uptake of any soil constituent or on rhizosphere community, indicating that plants and their associated microbial communities adapted to this environment are resilient to extremes in photoperiod. Lead uptake was not significant in any plant species and had no effect on the rhizosphere. Antimony increased the percentage composition of Saprospirales in the rhizospheres of two of the three plants, indicating an interaction between this bacterial order and antimony. Antimony uptake by white spruce (Picea glauca) was considerable, with a mean concentration of 1731 mg kg^?1 in roots, while mean shoot concentration was only 155 mg kg^?1, indicating its potential to phytostabilize this heavy metal. Although antimony had the strongest impact on the rhizosphere bacterial community, it was also readily accumulated by the grass and tree.