The future of isoprene emission from leaves, canopies and landscapes

Abstract

Isoprene emission from plants plays a dominant role in atmospheric chemistry. Predicting how isoprene emission may change in the future will help predict changes in atmospheric oxidant, greenhouse gas and secondary organic aerosol concentrations in the future atmosphere. At the leaf-scale, an increase in isoprene emission with increasing temperature is offset by a reduction in isoprene emission rate caused by increased CO2. At the canopy scale, increased leaf area index in elevated CO2 can offset the reduction in leaf-scale isoprene emission caused by elevated CO2. At the landscape scale, a reduction in forest coverage may decrease, while forest fertilization and community composition dynamics are likely to cause an increase in the global isoprene emission rate. Here we review the potential for changes in the isoprene emission rate at all of these scales. When considered together, it is likely that these interacting effects will result in an increase in the emission of the most abundant plant volatile, isoprene, from the biosphere to the atmosphere in the future. About the same amount of isoprene is emitted from vegetation to the atmosphere as all other non-methane hydrocarbons combined. Isoprene emission is very sensitive to environmental variables, especially variables likely to change in the future such as temperature and carbon dioxide concentration. These will affect isoprene emission both directly because of changes at the leaf level and indirectly as a result of landscape level effects of global change. We review what is known about how isoprene emission will change in the future and conclude that, on balance, isoprene emission is likely to be greater in the future than it is today. © 2014 John Wiley & Sons Ltd.