Observations of the uptake of carbonyl sulfide (COS) by trees under elevated atmospheric carbon dioxide concentrations

Global change forces ecosystems to adapt to elevated atmospheric concentrations of carbon dioxide (CO<sub>2</sub>). We understand that carbonyl sulfide (COS), a trace gas which is involved in building up the stratospheric sulfate aerosol layer, is taken up by vegetation with the same triad of the enzymes which are metabolizing CO<sub>2</sub>, i.e. ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEP-Co) and carbonic anhydrase (CA). Therefore, we discuss a physiological/biochemical acclimation of these enzymes affecting the sink strength of vegetation for COS. We investigated the acclimation of two European tree species, <i>Fagus sylvatica</i> and <i>Quercus ilex</i>, grown inside chambers under elevated CO<sub>2</sub>, and determined the exchange characteristics and the content of CA after a 1–2 yr period of acclimation from 350 ppm to 800 ppm CO<sub>2</sub>. We demonstrate that a compensation point, by definition, does not exist. Instead, we propose to discuss a point of uptake affinity (PUA). The results indicate that such a PUA, the CA activity and the deposition velocities may change and may cause a decrease of the COS uptake by plant ecosystems, at least as long as the enzyme acclimation to CO<sub>2</sub> is not surpassed by an increase of atmospheric COS. As a consequence, the atmospheric COS level may rise causing an increase of the radiative forcing in the troposphere. However, this increase is counterbalanced by the stronger input of this trace gas into the stratosphere causing a stronger energy reflection by the stratospheric sulfur aerosol into space (Brühl et al., 2012). These data are very preliminary but may trigger a discussion on COS uptake acclimation to foster measurements with modern analytical instruments

The effect of flooding on the exchange of the volatile C₂-compounds ethanol, acetaldehyde and acetic acid between leaves of Amazonian floodplain tree species and the atmosphere

The effect of root inundation on the leaf emissions of ethanol, acetaldehyde and acetic acid in relation to assimilation and transpiration was investigated with 2–3 years old tree seedlings of four Amazonian floodplain species by applying dynamic cuvette systems under greenhouse conditions. Emissions were monitored over a period of several days of inundation using a combination of Proton Transfer Reaction Mass Spectrometry (PTR-MS) and conventional techniques (HPLC, ion chromatography). Under non-flooded conditions, none of the species exhibited measurable emissions of any of the compounds, but rather low deposition of acetaldehyde and acetic acid was observed instead. Tree species specific variations in deposition velocities were largely due to variations in stomatal conductance. Flooding of the roots resulted in leaf emissions of ethanol and acetaldehyde by all species, while emissions of acetic acid were only observed from the species exhibiting the highest ethanol and acetaldehyde emission rates. All three compounds showed a similar diurnal emission profile, each displaying an emission burst in the morning, followed by a decline in the evening. This concurrent behavior supports the conclusion, that all three compounds emitted by the leaves are derived from ethanol produced in the roots by alcoholic fermentation, transported to the leaves with the transpiration stream and finally partly converted to acetaldehyde and acetic acid by enzymatic processes. Co-emissions and peaking in the early morning suggest that root ethanol, after transportation with the transpiration stream to the leaves and enzymatic oxidation to acetaldehyde and acetate, is the metabolic precursor for all compounds emitted, though we can not totally exclude other production pathways. Emission rates substantially varied among tree species, with maxima differing by up to two orders of magnitude (25–1700 nmol m−2 min−1 for ethanol and 5–500 nmol m−2 min−1 for acetaldehyde). Acetic acid emissions reached 12 nmol m−2 min−1. The observed differences in emission rates between the tree species are discussed with respect to their root adaptive strategies to tolerate long term flooding, providing an indirect line of evidence that the root ethanol production is a major factor determining the foliar emissions. Species which develop morphological root structures allowing for enhanced root aeration produced less ethanol and showed much lower emissions compared to species which lack gas transporting systems, and respond to flooding with substantially enhanced fermentation rates and a non-trivial loss of carbon to the atmosphere. The pronounced differences in the relative emissions of ethanol to acetaldehyde and acetic acid between the tree species indicate that not only the ethanol production in the roots but also the metabolic conversion in the leaf is an important factor determining the release of these compounds to the atmosphere

"Earth observation for land-atmosphere interaction science", Preface

Non peer reviewe

The effect of flooding on the exchange of the volatile C₂-compounds ethanol, acetaldehyde and acetic acid between leaves of Amazonian floodplain tree species and the atmosphere

International audienceThe effect of root inundation on the leaf emissions of ethanol, acetaldehyde and acetic acid was investigated with 2?3 years old tree seedlings of four Amazonian floodplain species by applying dynamic cuvette systems under greenhouse conditions. Emissions were monitored over a period of several days of inundation using a combination of Proton Transfer Reaction Mass Spectrometry (PTR-MS) and conventional techniques (HPLC, ion chromatography). Under non-flooded conditions, none of the species exhibited significant emissions of any of the compounds. A slight deposition of acetaldehyde and acetic acid was mainly observed, instead. Tree species specific variations in deposition velocities were largely due to variations in stomatal conductance. Flooding of the roots resulted in leaf emissions of ethanol and acetaldehyde by all species, while emissions of acetic acid occurred only by the species exhibiting the highest ethanol and acetaldehyde emission rates. All three compounds showed a similar diurnal emission profile, each displaying an emission burst in the morning, followed by a decline in the evening. This concurrent behavior supports the conclusion, that all three compounds emitted by the leaves are derived from ethanol produced in the roots by alcoholic fermentation, transported to the leaves with the transpiration stream and finally partly converted to acetaldehyde and acetic acid by enzymatic processes. Co-emissions and peaking in the early morning confirmed that root ethanol, after transportation with the transpiration stream to the leaves and enzymatic oxidation to acetaldehyde and acetate, is the metabolic precursor for all compounds emitted. Emission rates substantially varied among tree species, with maxima differing by up to two orders of magnitude (3?200 nmol m?2 min?1 for ethanol and 5?500 nmol m?2 min?1 for acetaldehyde). Acetic acid emissions reached 12 nmol m?2 min?1. The observed differences in emission rates between the tree species are discussed with respect to their root adaptive strategies to tolerate long term flooding, providing an indirect line of evidence that the root ethanol production is a major factor determining the foliar emissions. Species which develop morphological root structures allowing for enhanced root aeration produced less ethanol and showed much lower emissions compared to species which lack gas transporting systems, and respond to flooding with substantially enhanced fermentation rates. The pronounced differences in the relative emissions of ethanol to acetaldehyde and acetic acid between the tree species indicate that not only the ethanol production in the roots but also the metabolic conversion in the leaf is an important factor determining the release of these compounds to the atmosphere

Unexpected seasonality in quantity and composition of Amazon rainforest air reactivity

The hydroxyl radical (OH) removes most atmospheric pollutants from air. The loss frequency of OH radicals due to the combined effect of all gas-phase OH reactive species is a measureable quantity termed total OH reactivity. Here we present total OH reactivity observations in pristine Amazon rainforest air, as a function of season, time-of-day and height (0–80 m). Total OH reactivity is low during wet (10 s^(−1)) and high during dry season (62 s^(−1)). Comparison to individually measured trace gases reveals strong variation in unaccounted for OH reactivity, from 5 to 15% missing in wet-season afternoons to mostly unknown (average 79%) during dry season. During dry-season afternoons isoprene, considered the dominant reagent with OH in rainforests, only accounts for ~20% of the total OH reactivity. Vertical profiles of OH reactivity are shaped by biogenic emissions, photochemistry and turbulent mixing. The rainforest floor was identified as a significant but poorly characterized source of OH reactivity

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.JRC.H.7-Climate Risk Managemen

Atmospheric mixing ratios of methyl ethyl ketone (2-butanone) in tropical, boreal, temperate and marine environments

Methyl ethyl ketone (MEK) enters the atmosphere following direct emission from vegetation and anthropogenic activities, as well as being produced by the gas-phase oxidation of volatile organic compounds (VOCs) such as n-butane. This study presents the first overview of ambient MEK measurements at six different locations, characteristic of forested, urban and marine environments. In order to understand better the occurrence and behaviour of MEK in the atmosphere, we analyse diel cycles of MEK mixing ratios, vertical profiles, ecosystem flux data, and HYSPLIT back trajectories, and compare with co-measured VOCs. MEK measurements were primarily conducted with proton-transfer-reaction mass spectrometer (PTR-MS) instruments. Results from the sites under biogenic influence demonstrate that vegetation is an important source of MEK. The diel cycle of MEK follows that of ambient temperature and the forest structure plays an important role in air mixing. At such sites, a high correlation of MEK with acetone was observed (e.g. r2 = 0.96 for the SMEAR Estonia site in a remote hemiboreal forest in Tartumaa, Estonia, and r2 = 0.89 at the ATTO pristine tropical rainforest site in central Amazonia). Under polluted conditions, we observed strongly enhanced MEK mixing ratios. Overall, the MEK mixing ratios and flux data presented here indicate that both biogenic and anthropogenic sources contribute to its occurrence in the global atmosphere