Increases in volatile organic compound emissions of Scots pine in response to elevated ozone and warming are modified by herbivory and soil nitrogen availability

Climate change in the boreal forests include, e.g., warming, increased tropospheric ozone concentration, higher nitrogen (N) deposition and increased risk of insect outbreaks. Climate change influences emissions of biogenic volatile organic compounds (BVOCs) affecting plant defense, communication and atmospheric feedbacks. We studied the effects of elevated temperature (ca. 1 °C), elevated ozone (ca. 1.5 × ambient), two soil N availability levels (prevailing and 120 kg N ha−1 a−1) and herbivory on BVOC emission rates, net photosynthesis and resin canals (BVOCs storage), of Scots pine (Pinus sylvestris) seedlings in an open-field exposure in central Finland. Shoot BVOCs were collected in July 2012 within a few days after feeding by larvae of pine-sawfly Acantholyda posticalis, a month later in August, and in May 2013. Elevated temperature caused twofold to fourfold increases in total emissions of non-oxygenated monoterpenes (MTs), oxygenated MTs and sesquiterpenes (SQTs) and several reactive compounds, and higher N enhanced some of these changes. Ozone and higher N together increased emissions of several MTs and total SQTs. Higher number of resin canals and higher net photosynthesis might have contributed to BVOC increases. Herbivory had the strongest effect on SQT emissions (threefold increase) shortly after feeding. In the following spring, herbivory reduced emission rates of some MTs, but also synergistically increased MTs emissions with temperature but suppressed the increase caused by ozone. Results suggest that warming and ozone, particularly in areas with increased soil N availability, can increase BVOC emissions from young boreal forests in the near future, and herbivory may modify these responses.