Microbial Competition in Polar Soils: A Review of an Understudied but Potentially Important Control on Productivity

biolog

Actinorhizal Alder Phytostabilization Alters Microbial Community Dynamics in Gold Mine Waste Rock from Northern Quebec: A Greenhouse Study.

Phytotechnologies are rapidly replacing conventional ex-situ remediation techniques as they have the added benefit of restoring aesthetic value, important in the reclamation of mine sites. Alders are pioneer species that can tolerate and proliferate in nutrient-poor, contaminated environments, largely due to symbiotic root associations with the N2-fixing bacteria, Frankia and ectomycorrhizal (ECM) fungi. In this study, we investigated the growth of two Frankia-inoculated (actinorhizal) alder species, A. crispa and A. glutinosa, in gold mine waste rock from northern Quebec. Alder species had similar survival rates and positively impacted soil quality and physico-chemical properties in similar ways, restoring soil pH to neutrality and reducing extractable metals up to two-fold, while not hyperaccumulating them into above-ground plant biomass. A. glutinosa outperformed A. crispa in terms of growth, as estimated by the seedling volume index (SVI), and root length. Pyrosequencing of the bacterial 16S rRNA gene for bacteria and the ribosomal internal transcribed spacer (ITS) region for fungi provided a comprehensive, direct characterization of microbial communities in gold mine waste rock and fine tailings. Plant- and treatment-specific shifts in soil microbial community compositions were observed in planted mine residues. Shannon diversity and the abundance of microbes involved in key ecosystem processes such as contaminant degradation (Sphingomonas, Sphingobium and Pseudomonas), metal sequestration (Brevundimonas and Caulobacter) and N2-fixation (Azotobacter, Mesorhizobium, Rhizobium and Pseudomonas) increased over time, i.e., as plants established in mine waste rock. Acetate mineralization and most probable number (MPN) assays showed that revegetation positively stimulated both bulk and rhizosphere communities, increasing microbial density (biomass increase of 2 orders of magnitude) and mineralization (five-fold). Genomic techniques proved useful in investigating tripartite (plant-bacteria-fungi) interactions during phytostabilization, contributing to our knowledge in this field of study

Alder rhizosphere and bulk soil pH after six months of growth in mine residues.

<p>Letters above columns denote significant differences between means (p<0.05), as determined by Tukey’s HSD test.</p

Principal coordinate analysis (PCoA) plot illustrating ecological relatedness of RZ and BK soil microbial communities with 22.4% variance explained.

<p>Principal coordinate analysis (PCoA) plot illustrating ecological relatedness of RZ and BK soil microbial communities with 22.4% variance explained.</p

THB population enumeration for alder rhizosphere, alder bulk and control soils initially, i.e. at t = 0 (healthy greenhouse alders) and at t = f (6 months of growth in mine residues) with and without the addition of woodchips as a soil amendment.

<p>THB population enumeration for alder rhizosphere, alder bulk and control soils initially, i.e. at t = 0 (healthy greenhouse alders) and at t = f (6 months of growth in mine residues) with and without the addition of woodchips as a soil amendment.</p

Alder rhizosphere and bulk soil class-level bacterial community profiles after six (6) months of growth, relative to unplanted controls.

<p>(Ac = <i>A</i>. <i>crispa</i>, Ag = <i>A</i>. <i>glutinosa</i>, NT = no treatment, WC = woodchips). Asterisks (*) denote orders designated incertae sedis.</p

Alder rhizosphere and bulk soil family-level bacterial community profiles after six (6) months of growth, relative to unplanted controls.

<p>(Ac = <i>A</i>. <i>crispa</i>, Ag = <i>A</i>. <i>glutinosa</i>, NT = no treatment, WC = woodchips). Asterisks (*) denote orders designated incertae sedis.</p

Alder growth parameters after six months of growth in mine residues.

<p><b>(A) Biomass expressed as the seedling volume index (SVI); (B) Root length; (C) Root (dry) weight and (D) nodule (dry) weight.</b> Different letters denote significant differences of the mean as determined by Tukey’s HSD test.</p

Alder rhizosphere and bulk soil metal concentrations after six (6) months of growth.

<p>Alder rhizosphere and bulk soil metal concentrations after six (6) months of growth.</p

Alder rhizosphere (RZ) and bulk (BK) soil fungal (ITS) community profiles after six (6) months of growth in mine residues relative to initial (t = 0) controls.

<p>(Ac = <i>A</i>. <i>crispa</i>, Ag = <i>A</i>. <i>glutinosa</i>, NT = no treatment, WC = woodchips).</p