Effect of Exposure to UVA Radiation on Photosynthesis and Isoprene Emission in Populus × Euroamericana

Isoprene, which accounts for about 40% of the global emission of biogenic volatile organic compounds, plays a dual role in the plant-environment interactions. Outside the plants, isoprene can substantially increase the amount of tropospheric ozone in the atmosphere, whereas in plants isoprene plays a protective role under different stress conditions. The magnitude of isoprene emissions may be altered by increasing UVA radiation. We examined the effects of acute UVA radiation on carbon assimilation, isoprene emission, and photochemical reflectance index (PRI) in Populus x euroamericana saplings. Plants were exposed to either ambient UVA (30 W m-2) or enhanced UVA (60, 90 and 120 W m-2) radiation until the treated leaves had shown stable values of photosynthesis. Our results show that the inhibition of photosynthesis and stomatal conductance induced by high UVA radiation was mirrored by similar reduction in PRI. In contrast, isoprene emission was strongly stimulated by increasing doses of UVA radiation, confirming that isoprene formation may have direct or indirect functions in increasing plant tolerance to stresses. These findings may be likely relevant to predict the emissions of isoprenoid in globally changing environmental condition, global atmospheric chemistry, carbon cycles and climate.