Antioxidant enzymes protect cells against oxidative stress and are associated with stress tolerance and longevity. In animals, variation in their activities has been shown to relate to species ecology, but in plants, comparative studies with wild species are rare. We investigated activities of five antioxidant enzymes – ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), peroxidase (POX), and superoxide dismutase (SOD) – in roots of four perennial graminoid wetland species over a growing season to find out whether differences in root turnover or habitat preferences would be associated with variation in seasonal patterns of antioxidant enzyme activities. The investigated species differ in their root turnover strategies (fine roots senesce in the fall or fine roots survive the winter) and habitat preferences (nutrient-poor vs. productive wetlands). Roots were collected both in the field and from garden-grown plants. Antioxidant enzyme activities were higher and lipid peroxidation rates lower in species with annual root systems, and for species of the nutrient-poor wetland, compared with perennial roots and species of productive wetlands, respectively. There was variation in the activities of individual antioxidant enzymes, but discriminant analyses with all enzymes revealed a clear picture, indicating consistent associations of antioxidant enzyme activities with the type of root turnover strategy and with the preferred habitat. We conclude that antioxidant enzyme activities in plant roots are associated with the species' ecological strategies and can be used as traits for the characterization of the species' position along plant economics spectrum.

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Abstract:Planting trees is an important step in re-establishing functioning forest ecosystems after industrial land disturbances. Conventional planting practices create forests with evenly spaced trees, at low density, which maximizes individual tree growing space but delays the time until crown closure, potentially for decades. In this study, the first operational cluster planting trial for reclaimed boreal forest, we examined first year tree growth and vegetation competition results of a cluster planting trial in which trembling aspen (Populus tremuloides) trees were planted in clusters of 4, 10, or 20 trees with an internal spacing of 0.25 m along with non-clustered controls. Clustering of aspen seedlings had a measurable impact on the relative proportions of tree and competing vegetation cover with increased tree cover and decreased forb cover in the 10 and 20 seedling clusters compared to the controls. Average seedling height and first year height growth were similar across all cluster treatments but tended to be higher in the clusters, likely due to the suppression of competing vegetation. Operationally, there are still many questions to be answered before this practice can be implemented in a large scale across the landscape. However, based on our initial results, we believe that cluster planting has the potential to become a valuable tool for reclamation practitioners.

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