Reclaiming to Brackish Wetlands in the Alberta Oil Sands: Comparison of Responses to Sodium Concentrations by <i>Carex atherodes</i> and <i>Carex aquatilis</i>

• Main Authors: Lilyan C. Glaeser, Melissa House, Dale H. Vitt
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: Plants
• Subjects: Alberta; boreal; <i>Carex aquatilis</i>; <i>Carex atherodes</i>; oil sands reclamation; Sandhill Wetland
• Online Access: https://www.mdpi.com/2223-7747/10/8/1511

The variation in sodium concentrations in waters of natural fens and marshes on the western Canadian landscape provides a background for choosing the appropriate plants for wetland reclamation. Broad tolerances to salinity are especially important for reclamation trials on saline-rich ‘in-pits’ that were left from open-pit oil sands mining. One such species, <i>Carex aquatilis</i>, has been identified as a key species in early reclamation attempts; however, at the Sandhill Wetland on the Syncrude Canada oil sands lease, this species has aggressively colonized, dominating parts of the wetland and limiting species diversity. A second species, also widespread on natural lake shores and marshes, is <i>Carex atherodes</i>, with field observations suggesting a broad tolerance to salinity. Here, we examine the responses of this species to a series of sodium concentrations and compare these to those of <i>C. aquatilis.</i> In particular, we addressed three questions: (1) How do structural attributes of <i>C. atherodes</i> respond to a series of Na⁺ concentration treatments? (2) Are different structural responses related to the functional attributes of photosynthesis, stomatal conductance, and/or transpiration rate? (3) How do these responses compare to those of <i>C. aquatilis?</i> We implemented a phytotron experiment to test the responses of these two species to either five or six concentrations of sodium, ranging from 20 to 3000 mg Na⁺ L⁻¹. In general, structural responses of <i>C. atherodes</i> did not differ between 50 and 789 mg Na⁺ L⁻¹, while performances of all attributes were reduced at 1407 mg L⁻¹. Physiological attributes had high variation, but also had reduced performances at similar treatment levels. In comparison, a clear threshold was present for structural attributes in <i>Carex aquatilis</i> between 1650 and 2148 mg Na⁺ L⁻¹, while physiological attributes were reduced between 1035 to 1650 mg Na⁺ L⁻¹. These responses from <i>C. aquatilis</i> were similar to those previously reported. Na⁺ concentrations in porewater at the Sandhill Wetland in 2019 reached as high as 1200 mg Na⁺ L⁻¹, with natural subsaline and sodic sites ranging much higher. Although all of the plants in the treatments remained viable at the end of the experiment, these results indicate that Na⁺ concentrations above 1500–2000 mg Na⁺ L⁻¹ may inhibit the growth of these two species and decrease their competitive abilities.