In clonal plants, stolon and rhizome connections between ramets allow translocation of resources from established ramets to developing ramets (physiological integration). Because most environments are spatially heterogeneous, ramets establishing under unfavorable conditions can import essential resources from connected ramets growing in more favorable conditions. As a result, offspring ramets can colonize patches that would be uninhabitable for isolated or physiologically independent ramets. Industrial, agricultural and urban activities are responsible for high heavy metal concentrations in some soils. Understanding the influence of physiological integration in such situations is vital in devising strategies for restoration of such contaminated sites, and important in its own right for understanding how plants respond to adverse, and potentially lethal, environmental conditions. We investigated the physiological and morphological responses of the clonal plant specie Fragaria vesca growing in heterogeneous substrate with patches of contrasting quality (i.e. uncontaminated or heavy-metal-contaminated). This plant species frequently occurs in man-made habitats and thus is likely to be subjected to heavy-metal pollution. Due to spatial heterogeneity in soil characteristics, including heavy metal concentrations, and the ability of clonal plants to spread laterally, situations arise in which ramets located in uncontaminated microhabitats are connected to ramets in contaminated patches. We determined whether integration confers net benefits, in terms of photochemical activity, growth and survival, to ramets developing in soils contaminated with heavy metals. We also determined whether performance of ramets in favorable patches is affected by integration with ramets in unfavorable conditions. We studied the effects of physiological integration by comparing the performance of connected and isolated ramets in the same environments. A greenhouse experiment was performed to determine the capacity of integrated ramets to grow in contaminated conditions. We assessed the effects of copper and cadmium at different concentrations, corresponding with a control (no metals), normal range in soil and toxic concentration in soil, respectively: Cu (0, 25, 125 μg/g dry wt), and Cd (0, 1, 10 μg/g dry wt).
Results/Conclusions
Our results showed a benefit of integration especially for developing ramets growing in highly contaminated copper polluted environments. We conclude that integration improves the fitness of developing ramets of Fragaria vesca growing in heavy metal contaminated habitats, allowing clone systems to overcome the establishment risks and maintain their presence in these less favorable sites. Integration represents a mechanism for increasing survival in these stressful habitats, and this may have important implications for restoration of polluted soils.
