Effects of High Latitude Light Conditions on Gas Exchange and Morphology in Trifolium repens

Terrestrial plants play a central role in the Earth system, largely due to photosynthesis and transpiration. Stomata are the gateways that connect the interior of plants with their surrounding atmosphere, regulating both water loss through transpiration and uptake of CO2 for photosynthesis. Opening and closure of stomata are actively regulated in response to a range of internal and environmental signals, enabling plants to balance this trade-off. Models of vegetation processes, including stomatal conductance, are incorporated in Earth System Models that are used to study the components of the Earth system and climate change. The unique light conditions at high latitudes include an extended twilight period, characterised by a high proportion of blue light, that can last from sunset until sunrise for parts of the growing season. Plants perceive blue light as a specific signal that regulates many developmental and physiological responses, such as stomatal opening. This thesis investigates how gas exchange, as well as morphological traits, are affected by the extended twilight period at high latitudes in Trifolium repens–an agriculturally important species with a broad natural distribution. Experiments were carried out in controlled growth conditions in order to isolate the effect of low-intensity blue light at night. Three T. repens “types” were compared: Two cultivars (Milkanova and Litago), and field-collected individuals from Northern Norway (~69–70°N). The results of this study indicate that the extended twilight at high latitudes has the potential to increase stomatal conductance and affect agriculturally relevant traits. The increase in stomatal conductance did not seem to be accompanied by increased photosynthesis. This may have implications for model representation of agricultural landscapes at high latitudes, which has the potential to cover larger areas in the future due to climate change.