Plant physiological responses –
Work package 2.1

The applied treatments are likely to affect the physiology of the plants directly inducing short and long-term adjustments of the plants to acclimate to the new conditions through a complex sequence of physiological up- and down-regulation processes. The project will study these short and long-term adjustments for different plant species within all single and combined treatments, and also after short-term exposure to other stress factors. Particular focus will be devoted to seasonal effects and changes in the responses, because the expected changes in the length of the growing season and weather periodicity have the potential to profoundly change the utilization patterns of energy, water and carbon within the plant species.

The studies will include in situ measurements of the leaf gas exchange (CO₂ and water vapor) with portable gas exchange equipment to quantify changes in net photosynthesis, dark respiration, stomatal conductance, water-use efficiency and nitrogen-use efficiency. In addition some parameters related to light and CO₂ response curves (maximum carboxylation rate of rubisco and maximum electron transport rate) will be investigated. After the measurements, the leaves will be harvested for analyses of leaf area, mass and N content. The measurements will be done at regular intervals throughout the experiment and include campaigns with shorter frequency during the beginning and the end of the growing seasons and after long period of drought, when we expect the most pronounced treatment effects. Analyses of primary metabolites and pigments of particular relevance for the photosynthesis and of secondary metabolites will also include longer-term treatment effects on the leaf chemistry of the harvested leaves with particular relevance for the quality of the food source of herbivores.

Changes in CO₂ and climatic conditions may increase or decrease the susceptibility for other natural and anthropogenic sources of stress (McLaughlin and Percy 1999; Wall 2001). Therefore plant responses to short-term (30-60 min) exposure to single or combined increased ozone and UV-B levels will be investigated in selected treatments in the field. This will be done during a few campaigns in selected years. The responses to these additional combinations of stress factors will be measured as effects on the gas exchange and as chlorophyll fluorescence. We will try to introduce and develop a method for studying the buffer capacity of leaves in relation to stress exposure and climate change.