Assessing arbuscular mycorrhizal plant metal uptake and soil metal bioavailability among ‘dwarf’ sunflowers in a stratified compartmental growth environment

Abstract

Using the micronutrient zinc (Zn) as a metal contaminant, a stratified compartmental pot greenhouse experiment involving ‘dwarf’ sunflowers and an arbuscular mycorrhizal (AM) fungus was designed to assess the role of AM symbiosis toward plant growth and metal uptake, and to differentiate its impact toward edaphic parameters across different soil strata. Consistent with previous hypotheses, AM plants contained up to 40% lower metal concentrations in their shoots than non-AM plants, particularly at the highest soil Zn levels (200 and 400 mg Zn kg⁻¹ dry soil); this, corresponding with an enhanced growth status among AM plants. Upon assessing the soil Zn concentrations and pH, AM treatments also tended to have higher soil Zn levels and more alkaline conditions compared to non-AM treatments. This was found especially in the topmost soil stratum where AM root colonization was deemed most active as evidenced by a higher frequency of extraradical hyphae, vesicles, and arbuscules. Together, these effects were putatively linked to the AM-induced mechanism of metal biosorption known to modulate soil nutrient bioavailability and even delay the onset of metal toxicity.

Keywords:

• Helianthus annuus L. var. Pacino
• Glomus intraradices Schenck & Smith
• arbuscular mycorrhizal symbiosis
• metal stress tolerance
• soil resilience

Acknowledgements

The authors thank Dr N. DeSilva (Dept. Earth Sciences, University of Ottawa) for ICP OES analyses, and also recognize the insightful commentary provided by the Editor and both anonymous reviewers. This study was made possible by a Canada Graduate Scholarship to PA and a Discovery Grant to CC from the Natural Science and Engineering Research Council of Canada.