Do insect outbreaks on mountain birch affect capacity of subarctic vegetation to form secondary organic aerosols?
Jarmo Holopainen, Department of Environmental and Biological Sciences, University of Eastern Finland
Aerosols and clouds have properties to reflect solar radiation (albedo) and influence on the Earth’s radiation balance and climate. Boreal forests may emit sufficiently large amounts of organic vapours to modify cloud albedo and cool the climate by formation of secondary organic aerosols (SOA) and cloud condensation nuclei (CCN). Insect outbreaks in boreal forests may significantly increase emissions of biogenic volatile organic compounds (BVOCs) and stimulated formation of SOA e.g. via ozonolysis.
Mountain birch (Betula pubescens ssp. czerepanovii) is a significant emitter of BVOCs in subarctic area and this tree species is known to suffer frequent warming related outbreaks by Geometrid moths. We measured mountain birch BVOC emissions at the Kevo subarctic research station in Utsjoki, Finland to see effects of herbivory on emission rates and BVOC composition. Furthermore, in laboratory experiments we assessed the impact of BVOC emissions on SOA formation via ozonolysis using reaction chambers made of UV-transparent Teflon film.
Our results show that herbivore-induced VOC emissions were strongly dependent on larval density on plants. In the ozonolysis experiments using reaction chambers, BVOCs from plants fed by larvae increased new particle formation by nucleation. Also increased SOA mass loadings from insect damaged plants were detected. The role of herbivory-driven volatiles in biosphere-atmosphere feedbacks under the warming of subarctic is discussed.
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