Enter Zoom Meeting


Biogenic Volatile Organic Compounds (bVOCs) of Terrestrial Ecosystems – the Integration of Plants and Microbes into Fluxes

Biogenic volatile organic compounds (bVOCs) are global chemical signatures of life. bVOCs comprise chemically diverse gaseous compounds of biological origin and are emitted from and consumed in terrestrial ecosystems. We consider biological sources and sinks being mainly plants and soil life, especially the microbiota. bVOCs are receiving an increasing scientific interest since breakthroughs in analytics of compounds but also of plants and microbiota facilitate an integrative understanding.
bVOCs have various environmental functions. Some impact on the oxidative capacity of the troposphere, stratospheric ozone destruction, and contribute to aerosol formation. Others are involved in chemical signaling between plants, animals and microbes in terrestrial ecosystems and hence, connect organisms’ activities and behaviors beyond the canonical trophic foodweb theory. In the era of the anthropocene, land use and associated human forces alter bVOC flux dynamics by changing ecosystems and their properties.
Understanding bVOCs fluxes in and from terrestrial ecosystems has two conceptual dimensions. (a) They are ecological interaction signals and thus, are affecting ecological interactions and ecosystem functioning - which includes plant production in agriculture - and (b) they are relevant for atmospheric chemistry and thus land-atmosphere interactions. Both dimensions are inherently intertwined and can be seen as two sides of the same coin.
We would like to merge both dimensions in one single session at the EGU Biogeosciences Division to trigger discussions on future research perspectives - e.g. how to quantitatively determine and/or predict bVOC fluxes by considering interactions of biological actors. Also novel insights in the topic, and methodological developments and new approaches are highly welcomed.

Co-organized by AS3/SSS8
Convener: Steffen Kolb | Co-conveners: Marcela HernandezECSECS, Riikka Rinnan
| Tue, 24 May, 13:20–14:42 (CEST)
Room 3.16/17

Tue, 24 May, 13:20–14:50

Chairpersons: Marcela Hernandez, Steffen Kolb

Ryan Vella et al.

Earth system models (ESMs) are state-of-the-art models which integrate previously separate models of the ocean, atmosphere and vegetation in one comprehensive modelling system enabling the investigation of interactive feedbacks between different components of the Earth system. Global isoprene and monoterpene emissions from terrestrial vegetation, which represents the most important source of VOCs in the Earth system, are needed for a suitable representation in global and regional chemical transport models given their impacts on the atmosphere. Consequently, to accurately determine the budget of isoprene and monoterpenes in the atmosphere, adequate emissions from the terrestrial vegetation are a requirement for input into regional and global scale chemistry-transport or chemistry-climate models. Due to the feedbacks of vegetation activity involving interactions with the weather and climate, a coupled modelling system between vegetation and atmospheric chemistry is a recommended tool to address the fate of biogenic volatile organic compounds (bVOCs). In this work, we present further development in linking LPJ-GUESS, a global dynamic vegetation model, to the atmospheric chemistry-enabled atmosphere-ocean general circulation model EMAC. We evaluate terrestrial bVOC emission estimates from the submodel ONEMIS in EMAC with (1) prescribed climatological vegetation boundary conditions at the land-atmosphere interface; and (2) dynamic vegetation states calculated in LPJ-GUESS (replacing the “offline” vegetation inputs). LPJ-GUESS-driven global emission estimates for isoprene and monoterpenes were found to be 599 Tg yr−1 and 111 Tg yr−1, respectively. Additionally, we evaluated the sensitivity of the new coupled system in doubling CO2 scenarios. Higher temperatures resulted in an increase in bVOC emissions (+47% and +69% for isoprene and monoterpenes, respectively), whereas CO2-fertilisation resulted in an increase of 18% in isoprene emissions and 37% in monoterpene emissions. We provide evidence that the new coupled model yields suitable estimates for global bVOC emissions that are responsive to vegetation dynamics, thus enabling further research in land-biosphere-atmosphere interactions.

How to cite: Vella, R., Forrest, M., Lelieveld, J., and Tost, H.: Incorporating vegetation dynamics for terrestrial isoprene and monoterpene emission estimates: Linking LPJ-GUESS (v4.0) with the EMAC modelling system (v2.54) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-914, https://doi.org/10.5194/egusphere-egu22-914, 2022.

Heidelinde Trimmel et al.

In the city centre of Vienna, Austria ozone (maximum 8 hour mean) mda8 exceedances of the threshold value of 120 μg/m³ can occur from as early as March until September, which coincides with the main local vegetation season. Biogenic volatile organic compounds (bVOCs), which are mainly emitted by forests, but also other vegetation as agricultural field crops and are precursor substances to atmospheric formaldehyde (HCHO). Thereby they contribute to the production of ozone in and around the city. On the other hand, vegetated areas reduce the ozone concentration by uptake via stomatal and cuticular pathways and soil uptake.

In this study the dependency of HCHO mixing ratios, obtained from path averaged MAX-DOAS UV retrievals over the Vienna city centre, on meteorological parameters (air temperature, global radiation, boundary layer height) and vegetation drought stress indicators are analysed, focusing on the difference between drought and non-drought conditions. Following indicators are used: standardized precipitation index (SPI), relative soil saturation from the Agricultural Risk Information System (ARIS), vapour pressure deficit and satellite-based photosynthetically active radiation anomaly (fAPAR) as well as solar-induced chlorophyll fluorescence (SIF).

A clear dependency of the HCHO on vegetation-related parameters and the area of origin of HCHO and its precursor substances is found. However, the strength of the relationship between the parameters changes depending on the vegetation status. The results of the observational HCHO analyses spanning 2017-2021 are compared with bVOCs estimates of the Model of Emissions of Gases and Aerosols from Nature (MEGAN). The observed ozone concentrations are compared with the ozone mixing ratios and dry deposition rates calculated by the chemical transport model developed at Meteorological Synthesizing Centre-West within the European Monitoring and Evaluation Program (EMEP MSC-W model), which includes the Deposition of Ozone for Stomatal Exchange (DO3SE) model, to better understand timing and magnitudes of sources and sinks. Possible consequences for exceedances of the mda8 ozone target value in the study region are discussed.

How to cite: Trimmel, H., Mayer, M., Schreier, S., Schmidt, C., Checa-Garcia, R., Eitzinger, J., Fitzky, A. C., Karl, T., Huszár, P., Karlický, J., Hamer, P., Koehler, P., and Frankenberg, C.: Analysis of the dependency of atmospheric formaldehyde - as a proxy for bVOC emissions - on vegetation status over a Central European city and potential implications for surface ozone exceedances, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2432, https://doi.org/10.5194/egusphere-egu22-2432, 2022.

Yi Jiao et al.

Permafrost in the north Polar Regions stores more than 1,500 Pg of organic carbon, which is nearly twice as much as the atmospheric carbon pool. As the Arctic region is experiencing unprecedented warming, accelerated decomposition in permafrost is potentially switching it to a hotspot of carbon emissions. In addition to the widely studies carbon dioxide and methane, permafrost may also be a source of biogenic volatile organic compounds (BVOCs), a reactive group of trace gases which have so far received much less attention. BVOCs can prolong the lifetime of methane through the depletion of hydroxyl radicals, contribute to ozone formation, and lead to the formation of secondary organic aerosol, and thus exert significant impact on climate forcing, especially in unpolluted Arctic region.

Here, we conducted in situ measurements of soil BVOC emissions on an actively degrading permafrost peatland during a growing season. We compared emissions along a gradient of landscape units from soil palsa and vegetated palsa to thaw slump, thaw pond and vegetated thaw pond. BVOC samples were collected onto absorbent cartridges using dynamic enclosure chamber method, and then analyzed with a gas chromatograph coupled with a mass spectrometer (GC/MS), based upon which the emission rates were calculated.

Results suggested that all landscapes units across the peatland showed net emissions of BVOCs during the summertime. Major BVOC groups included monoterpenes, sesquiterpenes, isoprene, hydrocarbons, methanol, acetone, other oxygenated VOCs and other compounds, and these groups were present in all landscape units. All VOC groups also exhibited seasonal and spatial variations across the different sampling months and landscape units. For example, the actively degrading thaw slump showed higher monoterpene emissions that other landscape units, while sesquiterpene emissions were highest from the vegetated thaw ponds. Principal component analysis further revealed temporal and spatial patterns in the relative compositions of the BVOC profiles. Our results show that soil BVOC emissions change in response to active permafrost thaw.

How to cite: Jiao, Y., Davie-Martin, C., Kramshøj, M., Christiansen, C., Lee, H., Althuizen, I., and Rinnan, R.: Volatile carbon emissions from a degrading permafrost peatland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3481, https://doi.org/10.5194/egusphere-egu22-3481, 2022.

Heidi Hellén et al.
Anne Fitzky et al.

Biogenic volatile organic compounds (BVOCs) emitted by plants consist of a broad range of gasses which serve purposes such as protecting against herbivores, communicating with insects and neighboring plants, or increasing the tolerance to environmental stresses. Evidence is accumulating that the composition of BVOC blends plays an important role in fulfilling these purposes. Constitutional emissions give insight into species-specific stress tolerance potentials and are an important first step in linking metabolism and function of co-occurring BVOCs. Here, we investigate the blend composition and interrelations among co-emitted BVOCs in unstressed and drought- and salt stressed seedlings of four broad-leaved tree species, Quercus robur, Fagus sylvatica, Betula pendula, and Carpinus betulus. BVOCs of Q. robur and F. sylvatica were mainly isoprene and monoterpenes, respectively. B. pendula had relatively high sesquiterpene emission; however, it made up only 1.7% of its total emissions while the VOC spectrum was dominated by methanol (∼72%). C. betulus was emitting methanol and monoterpenes in similar amounts compared to other species, casting doubt on its frequent classification as a close-to-zero VOC emitter. Under drought and salt stress the main emitted BVOCs of F. sylvatica and B. pendula slightly decreased, whereas an increase was observed for Q. robur and C. betulus. Beside these major BVOCs, a total of 22 BVOCs could be identified, with emission rates and blend compositions varying drastically between species and treatments. Principal component analyses among species and treatments revealed co-release of multiple compounds. In particular, new links between pathways and catabolites were indicated, e.g., correlated emission rates of methanol, sesquiterpenes (MVA pathway), and green leaf volatiles (hexanal, hexenyl acetate, and hexenal; LOX pathway) during unstressed conditions. Drought stress led to a decrease of all BVOC emissions except for a slight increase of isoprene emissions of Q. robur, which might be due to decoupling from the photosynthesis and led to emptying C storages. Hexenyl acetate (LOX) follows the same pattern as isoprene but might have decreased due to a long droughting period. Salt stress led to an increase of LOX-related BVOCs, and acetaldehyde which supports the hypothesis that acetaldehyde emissions are linked to the oxidation of C18 fatty acids of cell membranes. Our results thus indicate that certain BVOC emissions are highly interrelated, pointing toward the importance to improve our understanding of BVOC blends rather than targeting dominant BVOCs only.

How to cite: Fitzky, A., Peron, A., Kaser, L., Karl, T., Graus, M., Tholen, D., Pesendorfer, M., Mahmoud, M., Trimmel, H., Halbwirth, H., Sandén, H., and Rewald, B.: Diversity and interrelations among the constitutive BVOC emission blends and changes during salt and drought stress of four broad-leaved tree species at seedling stage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4844, https://doi.org/10.5194/egusphere-egu22-4844, 2022.

Saranya Kanukollu et al.

Managed grasslands are global sources of atmospheric methanol, which is one of the most abundant biogenic volatile organic compounds (bVOCs) in the atmosphere and promotes oxidative capacity for tropospheric and stratospheric ozone depletion. The phyllosphere is a favoured habitat of plant-colonizing methanol-utilizing methylotrophs, but their quantitative relevance for methanol consumption and ecosystem fluxes in the rhizosphere is unclear. Methanol utilizers of the plant-associated microbiota are key for the mitigation of methanol emission through consumption. However, information on grassland plant methylotrophs, their biodiversity and, metabolic traits, and thus key actors in the global methanol budget is largely lacking.

Two common plant species (Festuca arundinacea, Taraxacum officinale) of a grassland were investigated in pot experiments using soil as a growth substrate. We used radiotracers (14C-methanol) to evaluate potential methanol oxidation rates and 13C-methanol RNA stable isotope probing (SIP) and metagenomes to identify methanol utilizers.

Intact plants unveiled different methanol utilizer communities between plant compartments (phyllosphere, roots, and rhizosphere) but not between plant host species. Methanol utilizers of Gamma- and Betaproteobacteria colonized the phyllosphere. Whereas,Deltaproteobacteria, Gemmatimonadates, and Verrucomicrobiae were predominant in the rhizosphere. Metagenome assembled genomes (MAGs) revealed bacterial methanol dehydrogenases of known but also unexpected genera, such as Methylomirabilis, Methylooceanibacter, Gemmatimonas, and Verminephrobacter. Divergent methanol oxidation rates in both plant species but similarly high rates in the rhizosphere and phyllosphere were determined by 14C-methanol tracing of alive plant material.

Our study revealed eventually the rhizosphere as a hotspot for methanol consumption in grasslands. Differences between the methanol utilizer communities of the two plant species were not evident suggesting a negligible host effect. Our results suggest a model for methanol turnover in which both the sources (plants) and sinks (microbiota) of a bVOC are separated but in the same ecological unit.

How to cite: Kanukollu, S., Remus, R., Rücker, A. M., and Kolb, S.: Rhizosphere of grassland plants: A hot spot of methanol consumption driven by unusual methylotrophs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6044, https://doi.org/10.5194/egusphere-egu22-6044, 2022.

Jonas Hädeler et al.

Organic and inorganic volatile compounds containing one or two carbon atoms (C1, C2), such as carbon dioxide, methane, methanol, formaldehyde, carbon monoxide, chloromethane, formic acid, acetic acid, ethane and ethene are ubiquitous in the environment and play an important role in atmospheric physics and chemistry as they act as greenhouse gases, destroy stratospheric and tropospheric ozone and control the atmospheric oxidation capacity. Furthermore, these compounds play an important role in global carbon cycling. Up to now, most C1 and C2 compounds in the environment were associated to complex metabolic and enzymatic pathways in organisms or combustion processes of biomass. So far, it was not recognized that many C1 and C2 compounds in the geobiosphere might also have a common origin in methyl groups from methyl-substituted substrates that are cleaved by the iron-catalysed formation of methyl radicals.

We performed a set of laboratory experiments containing methyl-substituted substances, an iron species (e.g. hematite, ferrihydrite or bispidine-iron complexes for the better understanding of the mechanism), H2O2 for the activation of the iron species and ascorbic acid as a radical scavenger. The experiments were conducted under ambient conditions (atmospheric pressure and 22°C) and variable parameters such as pH value, substrate concentration and O2 saturation.

We show that a range of organic and inorganic C1 and C2 compounds can be produced by environmentally important methyl-substituted substances such as dimethyl sulfoxide (DMSO), methionine, choline, trimethylamine, synapyl alcohol (lignin component) and galacturonic acid methyl ester (pectin component). Applying isotopically labelled (2H/13C) methyl groups from DMSO and methionine we unambiguously demonstrate that labelled methane, ethane, methanol, formaldehyde and acetic acid are produced from methyl-substituted substances.

Based on our preliminary results we hypothesise that formation of methyl radicals by abiotic and possibly also by biochemical processes is ubiquitous in the environment with various heteroatom-methylated substrates. We propose that by generating methyl radicals formation of the entire set of C1 compounds with carbon oxidation states of -IV to +IV but also formation of C2 compounds is possible. The relative amounts of the formed individual C1 species might depend on the redox milieu and biogeochemical conditions such as the availability of methyl radical donors, iron species, pH, O2 concentration and possibly a range of other parameters.  To thoroughly understand, the chemistry behind these processes and to verify mechanistic scenarios, we also performed computational modeling based on density functional theory and ab-initio quantum-chemical studies.

The investigated methyl moieties are ubiquitous in the terrestrial and marine biosphere. Thus, for future studies we will put our assembled knowledge into practice and study these reactions in water and soil samples collected from the field.

How to cite: Hädeler, J., Lauer, R., Gunasekaran, V., Rheinberger, K., Comba, P., and Keppler, F.: Iron catalysed formation of methyl radicals as a common source of environmentally important volatile carbon compounds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6138, https://doi.org/10.5194/egusphere-egu22-6138, 2022.

Lejish Vettikkat et al.

Wetlands are well-known for their high emissions of methane to the atmosphere, but emissions of volatile organic compounds (VOCs) are also reported from wetlands. Wetlands cover about 2 % of the total land surface area and most of these wetlands are found in the boreal and tundra regions. A class of compounds called terpenes that include isoprene, monoterpenes, sesquiterpenes, and diterpenes make up 80% of the global biogenic volatile organic compound (BVOC) emissions. These compounds are highly reactive towards oxidants like ozone (O3), hydroxyl radicals (OH), and nitrate radicals (NO3) and form secondary organic aerosols in the atmosphere. Hence, quantifying the BVOC emissions accurately is crucial in determining the organic aerosol budget and constraining their contribution to climate-relevant processes such as new-particle formation and cloud formation.

In this study we performed ecosystem scale eddy covariance (EC) measurements of BVOCs and their oxidation products at Siikaneva, a southern Finnish boreal wetland (61o48' N, 24o09' E, 160 m a.s.l.), from 19th May 2021 to 28th June 2021 using a Vocus-proton transfer reaction mass spectrometer (Vocus-PTR) co-located with a sonic anemometer (METEK USA-1) at 10 Hz.  BVOCs were sampled from a platform, 2.5 m above the wetland using a high flow main inlet (5000 lpm), with core sampling of 5 lpm into the Vocus-PTR, which substantially reduced the wall losses of less volatile compounds such as sesquiterpenes, diterpenes, and oxygenated VOCs. The EC data were analyzed following standard correction procedures such as lag correction, coordinate rotation, and uncertainty analysis using the InnFLUX tool by Striednig et al. (2020). The high frequency attenuations of the fluxes were corrected using transfer functions estimated using the sensible heat flux cospectra.

We observed high emissions of isoprene, monoterpenes, sesquiterpenes and the first-ever emission fluxes of diterpenes from a wetland. The average normalized standard emission factor (EF) at standard photosynthetically active radiation of 1000 μmols m-2 s-1 and standard temperature of 30 oC for isoprene using the emission algorithm by Guenther et al. (2012) was determined as 1200 μmols m-2 day-1. For comparison, a relaxed eddy accumulation (REA) flux measurement study at the same site by Haapanala et al. (2006) had reported much lower EF of 240 μmols m-2 day-1. We observed sesquiterpene emissions reaching up to 50% of monoterpene emissions on average and occasionally even higher than monoterpenes emissions. For diterpenes, we found mean emissions of 0.4 μmols m-2 day-1.

During the campaign, the temperature peaked at 32 oC which is abnormally high for boreal environments and all the terpenoid emissions showed an exponential temperature dependence. The derived exponential temperature coefficient (Q10) value for isoprene was 4 times higher than the values used in the widely used MEGAN model. Our study reveals that VOC emissions from boreal environment are very sensitive to temperature change and since temperature is one of the main drivers of BVOC emission, anthropogenic global warming can induce much higher BVOC emissions in the future.

How to cite: Vettikkat, L., Miettinen, P., Buchholz, A., Rantala, P., Yu, H., Schallhart, S., and Schobesberger, S.: Eddy covariance measurements reveal high emissions of terpenes from a boreal fen, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6938, https://doi.org/10.5194/egusphere-egu22-6938, 2022.

Leslie Nuñez Lopez and Barbara Ervens

Formic and acetic acids are ubiquitous components in the atmospheric gas and condensed (clouds, particles, fogs) phases. They originate from various anthropogenic or biogenic sources.

Their production and loss processes in the atmosphere are usually assumed to occur by chemical oxidation processes only. In atmospheric models, their chemical formation and loss processes are described by oxidation reactions with abundant oxidants (e.g., OH, NO3 radicals).

However, lab and model studies suggest that bacteria can efficiently biodegrade these acids and similar organic compounds. Their highest metabolic activity of bacteria is thought to be limited to their time in warm clouds due to the presence of liquid water.


We use a process model with detailed descriptions of cloud microphysics, multiphase (gas/cloud) chemistry and biodegradation processes in individual cloud droplets. The model is initialized with data from the Puy de Dome observatory (Auvergne, France), where long-term data sets of chemical, microphysical and biological cloud data in a variety of air masses were collected.

The model description of the multiphase chemistry and cloud microphysics is based on well-established models. Bacterial processes are implemented using lab-derived biodegradation rates for various atmospherically relevant bacteria strains and conditions.


We perform model studies for a variety of cloud chemical, biological and microphysical parameter ranges to identify atmospheric conditions, under which biodegradation represents a major loss process of formic and acetic acids. Since the number of bacteria cells is much smaller than that of cloud droplets, we will discuss the importance of the accurate model representation of cloud droplet properties (number concentration, diameter, lifetime) for model results. 

Our study demonstrates that microbiota in the atmosphere interact with chemical compounds and affect their budgets. It shows the need to (i) extend current atmospheric chemistry models and (ii) provide information on microbiota distribution and activity.  Thus, our work represents a study at the interface of atmospheric sciences and biogeochemistry and gives new research perspectives for interdisciplinary efforts in these fields.

How to cite: Nuñez Lopez, L. and Ervens, B.: The role of bacterial biodegradation for atmospheric budgets of formic and acetic acids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7458, https://doi.org/10.5194/egusphere-egu22-7458, 2022.

Roger Seco et al.

Biogenic emissions of volatile organic compounds (BVOCs) are a crucial component of biosphere-atmosphere interactions. In northern latitudes, climate change is amplified by feedback processes in which BVOCs have a recognized, yet poorly quantified role, mainly due to a lack of measurements and concomitant modelling gaps. Hence, current Earth system models mostly rely on temperature responses measured on vegetation from lower latitudes, rendering their predictions highly uncertain.

We used Proton Transfer Reaction -Time of Flight- Mass Spectrometry (PTR-TOF-MS) and eddy covariance to measure ecosystem-level isoprene fluxes at two contrasting ecosystems in Sweden and Norway during an entire growing season. Measured fluxes showed that tundra isoprene emissions responded vigorously to temperature increases, with Q10 temperature coefficients of up to 20.8; that is 3.5 times the Q10 derived from the equivalent model results. Our results demonstrate that tundra vegetation possesses the potential to substantially boost its isoprene emissions in response to future rising temperatures, at rates that exceed the current Earth system model predictions.

How to cite: Seco, R., Holst, T., Davie-Martin, C. L., Simin, T., Guenther, A., Pirk, N., Rinne, J., and Rinnan, R.: Strong isoprene emission response to temperature in tundra vegetation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10663, https://doi.org/10.5194/egusphere-egu22-10663, 2022.

Christiane Werner et al.

Severe droughts endangers ecosystem functioning worldwide and can impact ecosystem-atmosphere exchange of water and carbon fluxes as well as biogenic volatile organic compound (BVOC) emissions. However, mechanisms driving alterations in ecosystem-atmosphere exchange of BVOCs during drought and recovery remain poorly understood. To disentangle complex ecosystem dynamics we imposed a 9.5-week drought on the Biosphere 2 tropical rainforest, a thirty-year old enclosed forest. We traced ecosystem scale interactions through a whole-ecosystem labelling approach in the Biosphere 2 Tropical Rainforest, the B2 Water, Atmosphere, and Life Dynamics (B2WALD) experiment. We analysed total ecosystem exchange, soil and leaf fluxes of H2O, CO2 and BVOCs, and their stable isotopes over five months. To trace changes in soil-plant-atmosphere interactions we labelled the ecosystem with a 13CO2-isotope.

Drought sequentially propagated through the vertical forest strata, with a rapid increase in vapor pressure deficit, the driving force of tree water loss, in the top canopy layer and early dry-down of the upper soil layer but delayed depletion of deep soil moisture. Gross primary production (GPP), ecosystem respiration (Reco), and evapotranspiration (ET) declined rapidly during early drought and moderately under severe drought. Interactions between plants and soil led to distinct patterns in the relative abundance of atmospheric BVOC concentrations as the drought progressed, serving as a diagnostic indicator of ecosystem drought stress, with isoprene indicating the onset of ET and GPP reduction and hexanal indicating their final decline under severe drought. Net uptake of isoprene and monoterpenes by the soil was influenced by both overlying atmospheric concentrations and soil moisture. During drought, the concentration normalized soil uptake capacity of monoterpenes increased relative to isoprene. This indicated greater persistence of monoterpene scavenging by soils under drought when plant monoterpene emissions were highest.

Ecosystem 13CO2-pulse-labeling showed that drought enhanced the mean residence times of freshly assimilated carbon- indicating down-regulation of carbon cycling velocity and delayed transport form leaves to trunk and roots. Despite reduced ecosystem carbon uptake and total VOC emissions, plants continued to allocate a similar proportion of fresh carbon to de novo VOC synthesis, as incorporation of 13C into both isoprene and monoterpenes remained high. Maintaining carbon allocation into VOC synthesis demonstrates the fundamental role of these compounds in protecting plants from heat stress and photooxidative damage. VOC uptake increased immediately upon rain rewetting.

These data highlight the importance of quantifying drought impacts on forest functioning beyond the intensity of (meteorological) drought, but also taking dynamics response of hydraulic regulation of different vegetation compounds and soil microbial activity of the forest into account.

Werner et al. 2021, Science 374, 1514 (2021), DOI: 10.1126/science.abj6789

How to cite: Werner, C., Meredith, L. K., and Ladd, S. N. and the B2WALD: Ecosystem BVOC fluxes during drought and recovery trace ecohydrological responses of the vegetation and soil microbial interactions - insights from an ecosystem-scale isotope labelling experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11637, https://doi.org/10.5194/egusphere-egu22-11637, 2022.

Jolanta Rieksta et al.

Insect herbivory amplifies the biogenic volatile organic compound (BVOCs) emissions into the atmosphere, where BVOCs participate in atmospheric chemistry processes. In the high latitudes, herbivory induced BVOCs are considered as a major contribution to the total plant BVOC emissions during periods of active insect herbivore feeding. However, current BVOC models do not quantify BVOC emissions upon insect herbivory. Including effects of herbivory in models would be especially relevant in order to model BVOC emissions in the Arctic, where insect herbivore pressure is expected to increase with climate change.

We gathered data from enclosure-based field studies conducted in the Subarctic, that assessed the effects of outbreak-causing geometrid moth larvae (Operophtera brumata and Epirrita autumnata) feeding on the BVOC emissions of the dominant tree species, mountain birch (Betula pubescens var. pumila (L.)). The feeding damage ranged from background herbivory to up to 100% defoliation, thus mimicking local insect outbreak conditions.

The leaf area based BVOC emissions from mountain birch increased linearly with increasing feeding damage up to a maximum of 15 %, depending on the BVOC group. After this maximum, BVOC emissions declined as the leaf area decreased.

These results provide quantitative relationships between leaf area eaten and the emission rate of atmospherically important BVOC groups in the Subarctic mountain birch forest. Our results have practical implications for incorporating the modelling of herbivory induced BVOC emissions into the mainstream VOC models such as MEGAN (Model of Emissions of Gases and Aerosols from Nature) or LPJ-GUESS (Lund-Potsdam-Jena General Ecosystem Simulator).

How to cite: Rieksta, J., Li, T., Lauge Borchmann, R., and Rinnan, R.: Quantitative relationships between insect herbivory severity and BVOC emissions in a Subarctic mountain birch forest, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11680, https://doi.org/10.5194/egusphere-egu22-11680, 2022.

Laura Meredith et al.

Volatile organic compounds (VOCs) are vigorously cycled by microbes as metabolic substrates and products and as signaling molecules. Yet, current microbial metabolomic studies predominantly focus on nonvolatile metabolites and overlook VOCs, which therefore represent a missing component of the metabolome. In metabolomic studies, it is important to know which compounds within metabolic pathways may be considered volatile to predict potentially overlooked compounds and potentially include VOC measurement approaches to capture them.

In this study, we adapted and automated an atmospheric vapor pressure predictive model for metabolomic research to calculate relative volatility indices (RVIs) for compounds in a metabolic pathway through identification of the compound’s functional groups. We then evaluated the importance of considering compound volatility in soil metabolomic studies by comparing the ability of a suite of complementary analytical tools (nuclear magnetic resonance (NMR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS)) to capture complete metabolic pathways in soil.

We found that the metabolites that were not detected by NMR, GC-MS, and FT-ICR-MS within metabolic pathways had significantly higher volatility than those that were detected, revealing a bias against volatile metabolites in standard metabolomics pipelines. Moreover, we show that including VOC-resolving measurements (proton transfer reaction time of flight mass spectrometry (PTR-TOF-MS)) captured the volatile compounds missed by other metabolomic techniques, and together, the combined approaches captured more complete microbial metabolic processes in soil.  Our results demonstrate the importance and prevalence of VOCs as metabolites in soil. Including volatile metabolites in metabolomics, both conceptually and in practice, will build a more comprehensive understanding of microbial processes across ecological communities.

How to cite: Meredith, L., Tfaily, M., Geffre, P., Graves, K., Riemer, K., Honeker, L., and Krechmer, J.: Microbial volatile organic compounds: important but overlooked in microbial systems studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12851, https://doi.org/10.5194/egusphere-egu22-12851, 2022.