Interactions between metal and drought stressors on plant water relationships and their effects at ecosystem level

Heavy metals influence plant traits that are relevant to its internal water status. Therefore, knowledge of metal effects on a plant’s ability to tolerate other stresses such as drought is important to ensure sustainability of restoration efforts in contaminated landscapes, often prone to drought. The aim of this thesis was to gain understanding how heavy metal contamination influences plant-water relationships and how this interacts with effects of a simultaneous drought. Levels ranging from organs to ecosystem processes were investigated. Chapter 1 briefly reviews published studies on interactions between metal and drought stress and highlights potential gaps in literature. Chapter 2 presents results of a 2-year outdoor lysimeter study on the effects of Cu-Ni toxicity on plant-water relationships using saplings of Acer rubrum, Betula papyrifera, and Quercus rubra. The study shows that under elevated metal levels the plants use less water but suffer drought symptoms even if there is water available. Chapter 3 investigates, using B. papyrifera, whether such metal effects on water use are a result of short-term exposure of roots on their water uptake capacity, or due to long-term structural damage e.g. on hydraulic architecture. Both effects were found, but were smaller than hypothesized. In Chapter 4 influence of metals on plant’s vulnerability to xylem embolisms in Acer rubrum saplings is found to be higher in the metal contaminated region of Sudbury, Ontario, compared to surrounding uncontaminated regions. Chapter 5 establishes guidelines and limitations for transporting leaves from field to laboratory when measuring leaf relative water content, a method that is important for studying plant water relations in the field. Finally, I conclude with a general overall summary of results and proposed suggestions for reclamation projects.