BVOC responses to realistic nitrogen fertilization and ozone exposure in silver birch

Emission of BVOC (Biogenic Volatile Organic Compounds) from plant leaves in response to ozone exposure (O-3) and nitrogen (N) fertilization is poorly understood. For the first time, BVOC emissions were explored in a forest tree species (silver birch, Betula pendula) exposed for two years to realistic levels of O-3 (35, 48 and 69 ppb as daylight average) and N (10, 30 and 70 kg ha(-1) yr(-1), applied weekly to the soil as ammonium nitrate). The main BVOCs emitted were: alpha-pinene, beta-pinene, limonene, ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and hexanal. Ozone exposure increased BVOC emission and reduced total leaf area. The effect on emission was stronger when a short-term O-3 metric (concentrations at the time of sampling) rather than a long-term one (AOT40) was used. The effect of O-3 on total leaf area was not able to compensate for the stimulation of emission, so that responses to O-3 at leaf and whole plant level were similar. Nitrogen fertilization increased total leaf area, decreased alpha-pinene and beta-pinene emission, and increased ocimene, hexanal and DMNT emission. The increase of leaf area changed the significance of the emission response to N fertilization for most compounds. Nitrogen fertilization mitigated the effects of O-3 exposure on total leaf area, while the combined effects of O-3 exposure and N fertilization on BVOC emission were additive and not synergistic. In conclusion, O-3 exposure and N fertilization have the potential to affect global BVOC via direct effects on plant emission rates and changes in leaf area.