Sensitivity of Norway spruce physiology and terpenoid emission dynamics to elevated ozone and elevated temperature under open-field exposure

Abstract

Volatile organic compounds (VOCs) emitted from vegetation to the atmosphere contribute to global climate change, but climate change factors also affect VOC emission from vegetation. Soil-grown Norway spruce seedlings were exposed to elevated ozone (1.4×ambient ozone concentration) and elevated temperature (ambient+1.3°C) alone and in combination as well as to ambient ozone and temperature treatments under open-field conditions. VOC emissions (mainly terpenoids), genes involved in early steps of plastidial monoterpene and isoprene synthesis, photosynthetic parameters and growth were measured. In July, when daytime elevated ozone concentrations had been over 40ppb, ozone doubled the total terpenoid emissions by increasing the emissions of many monoterpenes and sesquiterpenes. Elevated temperature changed the terpenoid profile by increasing the emissions of oxygenated monoterpenes, but did not influence total emissions. Terpenoid emission profiles also differed between elevated ozone alone and elevated ozone in combination with elevated temperature. In August, when daytime elevated ozone concentrations had been ca. 30ppb, significant treatment effects were not found. Ozone and temperature reduced the expression of DXS2B (1-deoxy-d-xylulose 5-phosphate synthase type II), and ozone that of DXR (1-deoxy-d-xylulose 5-phosphate reductoisomerase) in August. Elevated temperature reduced the stem diameter growth, net photosynthesis and stomatal conductance, but elevated ozone did not have effects on these parameters. Results suggest that elevated temperature may not modify the ozone responses, or vice versa, in terms of gas exchange, growth or total terpenoid emission rates of young Norway spruces in a near-future climate. However, observed changes in terpenoid emission profiles may be important in the future climate, as reactivity in the troposphere differs between individual terpenoids.