BVOC (Biogenic volatile organic compound) emission responses to climate change

All plants emit a wide range of volatile compounds such as nitric oxide, carbon monoxide, and non-methane volatile organic compounds, the so-called biogenic volatile organic compounds (BVOC). BVOC emissions have received increased scientific attention in the last two decades because BVOCs are highly reactive and, thus, may profoundly influence the chemical and physical properties of the atmosphere. The global carbon emitted as BVOCs is about 1.1 Pg per year, and is believed to be of the same order of magnitude than methane emissions. BVOC emissions are generally closely linked to carbon assimilation in many forest and agriforest species, which are the main BVOC emitters, but they play a contrasting role in the biosphere-atmosphere interactions. In fact, forest and agriforest vegetation is a dominant sink for the atmospheric CO2 and ties about 90% of the globe's biomass carbon. Thus, it plays, by mean of photosynthesis, a key role in mitigating global change. In contrast, BVOCs have an important, negative impact in atmospheric chemistry, because they play a major role in the production of tropospheric ozone and aerosols. BVOCs rapidly react with anthropogenic and natural compounds and particularly with nitrogen oxides in the atmosphere leading to the formation of tropospheric ozone and photochemical smog. Furthermore, BVOCs affect the residence time of other greenhouse gases (including methane), and may cause the formation of secondary aerosols, a component of PM10 in the atmosphere. This emphasizes the importance of biogenic emissions, and inventories of BVOC emissions are, thus, a key issue in atmospheric sciences. Moreover, given the importance of both BVOC emissions and carbon assimilation for the biosphere-atmosphere interactions, the consequences of climate change (rising [CO2] and temperature) for the biogeochemical carbon cycle and for the atmospheric chemistry are potentially extremely large. Thus, a thorough understanding of BVOC synthesis mechanisms and plant and ecosystem responses to climate change is required if future emissions are to be reliably predicted.
The CNR-Institute for Atmospheric Pollution (CNR-IIA) is strongly engaged on the impact of climate change on vegetation. Recent findings published by CNR-IIA have shown that climate change may have contrasting effects on isoprene (the most important BVOC, which has a lifetime of less than an hour and may account for up to 50% of the atmospheric loading of non-methane hydrocarbons) emitted by forest and agriforest vegetation. In studies on poplar exposed to free-air CO2 enrichment, it has been shown that rising [CO2] may reduce isoprene emission. However, it can be expected that rising temperature will increase the rate of isoprene emission. The trade-off between these contrasting effects is not known and may be mediated by primary physiological processes such as respiration. In order to improve our knowledge on these processes, we are currently studying the relationships between isoprene emission and plant respiration in trees exposed to rising CO2 and elevated temperature.