Isoprenoid emission response to changing light conditions of English oak, European beech and Norway spruce

Light is an important environmental factor controlling biogenic volatile organic compound (BVOC) emissions, but in natural conditions its impact is hard to separate from other influential factors such as temperature. We studied the light response of foliar BVOC emissions, photosynthesis and stomatal conductance on three common European tree species, namely English oak (Quercus robur), European beech (Fagus sylvatica) and two provenances of Norway spruce (Picea abies) in Taastrup, Denmark. Leaf scale measurements were performed on the lowest positioned branches of the tree in July 2015. Light intensity was increased in four steps (0, 500, 1000 and 1500 µmol m−2 s−1), whilst other chamber conditions such as temperature, humidity and CO2 levels were fixed. Whereas the emission rate differed between individuals of the same species, the relative contributions of compounds to the total isoprenoid emission remained similar. Whilst some compounds were species specific, the compounds α-pinene, camphene, 3-carene, limonene and eucalyptol were emitted by all of the measured tree species. Some compounds, like isoprene and sabinene, showed an increasing emission response with increasing light intensity, whereas other compounds, like camphene, had no significant emission response to light for most of the measured trees. English oak and European beech showed high light-dependent emission fractions from isoprene and sabinene, but other emitted compounds were light independent. For the two provenances of Norway spruce, the compounds α-pinene, 3-carene and eucalyptol showed high light-dependent fractions for many of the measured trees. This study highlights differences between compound emissions in their response to a change in light and a possible light independence for certain compounds, which might be valid for a wider range of tree species. This information could be of importance when improving emission models and to further emphasize the discussion regarding light or temperature dependencies for individual compounds across species.

Isoprenoid emission response to changing light conditions of English oak, European beech and Norway spruce

Light is an important environmental factor controlling biogenic volatile organic compound (BVOC) emissions, but in natural conditions its impact is hard to separate from other influential factors such as temperature. We studied the light response of foliar BVOC emissions, photosynthesis and stomatal conductance on three common European tree species, namely English oak (Quercus robur), European beech (Fagus sylvatica) and two provenances of Norway spruce (Picea abies) in Taastrup, Denmark. Leaf scale measurements were performed on the lowest positioned branches of the tree in July 2015. Light intensity was increased in four steps (0, 500, 1000 and 1500 μmol m−2 s−1), whilst other chamber conditions such as temperature, humidity and CO2 levels were fixed. Whereas the emission rate differed between individuals of the same species, the relative contributions of compounds to the total isoprenoid emission remained similar. Whilst some compounds were species specific, the compounds α-pinene, camphene, 3-carene, limonene and eucalyptol were emitted by all of the measured tree species. Some compounds, like isoprene and sabinene, showed an increasing emission response with increasing light intensity, whereas other compounds, like camphene, had no significant emission response to light for most of the measured trees. English oak and European beech showed high light-dependent emission fractions from isoprene and sabinene, but other emitted compounds were light-independent. For the two provenances of Norway spruce, the compounds α-pinene, 3-carene and eucalyptol showed high light-dependent fractions for many of the measured trees. This study highlights differences between compound emissions in their response to a change in light and a possible light independence for certain compounds, which might be valid for a wider range of tree species. This information could be of importance when improving emission models and to further emphasize the discussion regarding light or temperature dependencies for individual compounds across species.

Effects of Elevated CO2 and O3 Concentrations on Isoprenoid Emissions from Pinus tabulaeformis

Isoprene and monoterpenes have indirect effects on ozone concentration, methane lifetime and aerosol formation. At the same time, the atmospheric composition change (reflected in elevated CO2and O3concentrations) can affect the speciation of monoterpenes / isoprenoids and magnitude of isoprene and monoterpenes fluxes. Ambient concentrations of CO2and O3were 342 μmolmol-1and 40 nmolmol-1, respectively. The effects of elevated CO2(700 μmolmol-1) and O3(80 nmolmol-1) concentrations on isoprenoid emission rates and patterns fromPinustabulaeformiswere studied in open top chambers (OTCs). The released volatiles were quantified by thermal desorption and gas chromatography with flame ionization detector (GC-FID). The study showed that α-pinene was the main compound emitted from Ptabulaeformis, accounting for more 51.5 - 72.6% of the detected volatile compounds. The emissions of isoprene and monoterpenes were reduced in response to elevated CO2concentrations. Exposure to elevated O3for 3 years significantly promoted the isoprene and monoterpenes emissions (p<0.05). Compared with ambient, elevated O3concentration increased isoprene emission from Ptabulaeformisby about 270.5 ± 13.5%. The response of monoterpene emission to elevated O3may vary during the course of exposure to the pollutant. The patterns of monoterpene and isoprene emissions under combined elevated CO2and O3concentrations were similar to those under elevated CO2concentration alone.

Estimations of isoprenoid emission capacity from enclosure studies: measurements, data processing, quality and standardized measurement protocols

The capacity for volatile isoprenoid production under standardized environmental conditions at a certain time (ES, the emission factor) is a key characteristic in constructing isoprenoid emission inventories. However, there is large variation in published ES estimates for any given species partly driven by dynamic modifications in ES due to acclimation and stress responses. Here we review additional sources of variation in ES estimates that are due to measurement and analytical techniques and calculation and averaging procedures, and demonstrate that estimations of ES critically depend on applied experimental protocols and on data processing and reporting. A great variety of experimental setups has been used in the past, contributing to study-to-study variations in ES estimates. We suggest that past experimental data should be distributed into broad quality classes depending on whether the data can or cannot be considered quantitative based on rigorous experimental standards. Apart from analytical issues, the accuracy of ES values is strongly driven by extrapolation and integration errors introduced during data processing. Additional sources of error, especially in meta-database construction, can further arise from inconsistent use of units and expression bases of ES. We propose a standardized experimental protocol for BVOC estimations and highlight basic meta-information that we strongly recommend to report with any ES measurement. We conclude that standardization of experimental and calculation protocols and critical examination of past reports is essential for development of accurate emission factor databases.