BG3.5 | Forest Responses to Global Change
EDI
Forest Responses to Global Change
Convener: L. M Mercado | Co-conveners: Sophie Fauset, Mingkai Jiang, Klaske van Wijngaarden, Liz Hamilton, Johanna PihlbladECSECS
Orals
| Mon, 24 Apr, 14:00–18:00 (CEST)
 
Room 2.95
Posters on site
| Attendance Mon, 24 Apr, 10:45–12:30 (CEST)
 
Hall A
Posters virtual
| Attendance Mon, 24 Apr, 10:45–12:30 (CEST)
 
vHall BG
Orals |
Mon, 14:00
Mon, 10:45
Mon, 10:45
Forest ecosystems play a crucial role in the global carbon budget, with mature forests being the most important land carbon sink. . However, the capacity of terrestrial ecosystems to continue sequestering carbon under climate change remains unclear. In order to accurately predict their resilience to future warming, increasing CO2 concentrations, and subsequent feedback to the climate system, there is a need for improved understanding of forest responses at all scales, from physiology to the ecosystem level responses. We aim to gather new knowledge/data sets from global change experiments, remote sensing and modelling studies from forests across the world, including recent field warming and elevated CO2 experiments. We welcome work on organ- to ecosystem-level responses to warming and CO2 as well as work that helps to elucidate how such processes could be represented within vegetation modelling frameworks. With this session, we aim to broaden the mechanistic understanding of forest ecosystems and what their response to the imminent increases in atmospheric CO2 and temperature will mean for their capacity to sequester carbon.

Orals: Mon, 24 Apr | Room 2.95

Chairpersons: L. M Mercado, Sophie Fauset
14:00–14:05
14:05–14:15
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EGU23-11920
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ECS
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Highlight
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Virtual presentation
Manon Rumeau, Rob Mackenzie, Yolima Carillo, Fotis Sgouridis, Michaela Reay, and Sami Ullah

Forests under elevated atmospheric CO2 concentration as a result of climate change are expected to require more available nitrogen (N) to sustain the enhanced CO2 uptake for photosynthesis and C storage. Therefore, it is essential to evaluate how CO2 fumigation of forests will affect availability of N to trees. Main pathways to sustain the high N demand are increasing biological N fixation (BNF), increasing N turn-over and reducing N losses. The purpose of this research is to explore the effects of elevated CO2 on soil N cycling in a temperate forest under the Birmingham Institute of Forest Research (BIFoR) Free Air Carbon Dioxide Enrichment (FACE) facility. We hypothesize that under CO2 fertilization, trees will allocate more carbon belowground to enhance microbial activity resulting in an increase of all nitrogen fluxes (i.e. N mineralisation, N fixation and N gas emissions). Net mineralisation rates were measured in-situ every month over 10 months and gross mineralisation rates were measured in-situ in spring, summer and autumn using the 15N pool dilution method. BNF by free-living organisms was investigated using the 15N assimilation method and N2O production rates were measured using the 15N-Gas flux method. Net mineralisation was increased on average by 30% under elevated CO2, delivering an extra 24 kgN.ha-1.y-1, and by 80% during the budburst period (April). Gross ammonification and NH4+ immobilisation rates were also slightly higher under elevated CO2 by respectively 33% and 19%. Yet, nitrification, NO3 immobilisation and N2O emission rates were not affected, demonstrating that, ammonium and nitrate cycling responded differently to elevated CO2. In addition, under elevated CO2, soils were more concentrated in DOC, DON and ammonium (p<0.05). Soil respiration and fine root biomass were also significantly higher by respectively 25% and 40%. Together, these findings suggest that trees allocate more C belowground through a higher root production and exudation enhancing N mineralisation under elevated CO2. Yet, the effects of elevated CO2 on N cycling are focused on increasing soil NH4+ availability as NO3- availability, N2O emission and N2 fixation were not responsive to eCO2. Collectively, our results suggest that trees are able to control and shape the nitrogen cycling communities to cope with N limitation. Nonetheless, it is difficult to predict if that will be sufficient to delay or alleviate progressive nitrogen limitation under future climate.

How to cite: Rumeau, M., Mackenzie, R., Carillo, Y., Sgouridis, F., Reay, M., and Ullah, S.: Nitrogen cycling in forest soils under elevated CO2: response of a key soil nutrient to global change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11920, https://doi.org/10.5194/egusphere-egu23-11920, 2023.

14:15–14:25
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EGU23-8437
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ECS
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On-site presentation
Chunhui Zhan, René Orth, Hui Yang, Markus Reichstein, Sönke Zaehle, Anja Rammig, and Alexander Winkler

Carbon sequestration, particularly in forests, is assumed to increase with increasing atmospheric CO2 concentrations due to the CO2 fertilization effect on photosynthesis (CFE). Estimating the contemporary effect of increasing atmospheric CO2 on continuous measurements of gross primary production (GPP) in forest stands is still lacking as it is challenging to disentangle the CFE from other effects on GPP acting on long time scales such as climate variability, succession, land-cover change, and nutrient deposition. Here we introduce a statistical method, i.e., the “GPP residual” method, to estimate the effect of climate on GPP based on short-term variability, to remove it from the long-term signal, yielding the GPP residual that can be, at least partly, attributed to CFE.

We validate the applicability of this “GPP residual” method by testing whether it can accurately identify the CFE in simulations of the process-based land surface model QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system). We compare (i) the difference in the simulated GPP between historical simulations forced with transient and constant CO2 concentrations with (ii) the non-climatic GPP variations determined when applying the “GPP residual” method to the transient-CO2 simulation, and find encouraging agreement.

We next apply our approach to eddy-covariance derived GPP at 32 forested sites located in Europe and the US to quantify the CFE for each site and month-of-year in growing seasons. The median CFE across all site-months is 22 ± 6 % per 100 ppm change in CO2. We note that other effects, such as nitrogen deposition and land management, also influence the GPP residual and could be incorrectly attributed to CFE. Assuming that these more site-specific effects may partially cancel out across sites as random effects, the estimated median value still reflects the strength of CFE. However, causal research will be needed to disentangle these long-term effects which cannot be separated by time scale.

In summary, our study derives for the first time an observation-based estimation of the CO2 fertilization effect across forested ecosystems based on the eddy covariance record. Our results encourage future work to reconcile the uncertainties of the effect of increasing CO2 on the global carbon cycle as determined from models, experiments and observations.

How to cite: Zhan, C., Orth, R., Yang, H., Reichstein, M., Zaehle, S., Rammig, A., and Winkler, A.: The strength of CO2 fertilization in forests inferred from the eddy-covariance record, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8437, https://doi.org/10.5194/egusphere-egu23-8437, 2023.

14:25–14:35
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EGU23-5024
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On-site presentation
Jan Pisek, Ladislava Řezníčková, Kairi Adamson, and David Ellsworth

Leaves form the primary interface between plant physiology, CO2 in the atmosphere and energy (light). Plant productivity (i.e. carbon (C) gain) is primarily determined by the amount of leaf area, leaf orientation and distribution in space. Not much attention has been paid to possible changes in leaf orientation and distribution with elevated CO2 (eCO2), but its effect on plant growth could alter the proportions of sunlit and shaded leaf areas and feedback on carbohydrate available for further growth. We report on first measurements of leaf inclination angle distribution, foliage clumping in a native evergreen Eucalyptus woodland - the EucFACE experiment in Western Sydney, New South Wales, Australia - in ambient CO2 and exposed to +150 ppm elevated CO2 (eCO2). We found that a spherical leaf angle distribution, a common assumption in ecosystem modeling, was not an appropriate supposition for present species (Eucalyptus tereticornis Sm.; Eucalyptus amplifolia Naudin) at this site. Our measurements of leaf inclination angles from imagery indicated an erectophile, highly skewed unimodal leaf inclination angle distribution function. We conclude that despite the measured steeper angles under eCO2 concentrations, the leaf angle change is not significant and falls within the expected natural variability and uncertainties connected with the measurement method. The lack of a clear response of leaf orientation and foliage clumping to eCO2 concentration indicates that the previously produced datasets of leaf inclination angles and foliage clumping maps with Earth observation data may be suitable while modelling carbon and water cycles under climate change.

How to cite: Pisek, J., Řezníčková, L., Adamson, K., and Ellsworth, D.: How can elevated CO2 (eCO2) affect the vegetation structure of a mature evergreen Eucalyptus woodland – results from the Eucalyptus Free-Air CO2 Enrichment (EucFACE) experiment in Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5024, https://doi.org/10.5194/egusphere-egu23-5024, 2023.

14:35–14:55
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EGU23-586
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ECS
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solicited
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Highlight
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Virtual presentation
Mirindi E Dusenge, Maria Wittemann, Myriam Mujawamariya, Lasse Tarvainen, Elisée Ntawuhiganayo Bahati, Etienne Zibera, Bonaventure Ntirugulirwa, Danielle Way, Donat Nsabimana, Johan Uddling, Göran Wallin, Zorayda Restrepo Correa, Sebastian Gonzalez-Carro, Patrick Meir, and Adriana Sanchez

Tropical montane forests are among the most productive ecosystems within the tropical region and store a significant amount of carbon in live biomass. With ongoing global climate warming, tropical climates are also getting warmer. The productivity and climate feedbacks of future tropical montane forests depend on the ability of trees to acclimate their photosynthetic metabolism to these new, warmer conditions. However, knowledge of acclimation ability of photosynthesis and its underlying biochemical processes to warming in trees grown under natural field conditions is currently limited due to data scarcity. To reduce this knowledge gap, we used two separate field experiments located in Colombia (with 15 species) and Rwanda (16 species), and for each experiment, tree species were grown at three different sites along an elevation gradient differing in ambient air temperature. At all three sites, we measured the responses of net CO2 assimilation at different CO2 concentration (50 to 2000 ppm) and at different leaf temperatures (15 to 40 °C) in ≈ 3 years old trees. We used these data to derive key photosynthetic biochemical parameters (maximum Rubisco carboxylation capacity - Vcmax and maximum electron transport rate - Jmax) and their temperature sensitivity, as well as the thermal optimum of net photosynthesis (ToptA). We show that tropical montane tree species from the two continents are generally able to acclimate their ToptA by increasing in trees grown in warmer conditions, but the magnitude of change in ToptA differs among species from different successional groups (early- versus late succession) and climate of origin (lowland versus montane). Shifts in ToptA are largely driven by concomitant changes in thermal sensitivity parameters of underlying biochemical processes of photosynthesis (Vcmax and Jmax) with warming. We also show that, at a standard temperature of 25 °C, Vcmax is largely constant, while Jmax decreases with warming. Our findings indicate tropical montane tree species from Latin America and Africa can thermally acclimate their photosynthetic physiology, but that this thermal acclimation ability is related to species successional group and their climate of origin.

How to cite: Dusenge, M. E., Wittemann, M., Mujawamariya, M., Tarvainen, L., Ntawuhiganayo Bahati, E., Zibera, E., Ntirugulirwa, B., Way, D., Nsabimana, D., Uddling, J., Wallin, G., Restrepo Correa, Z., Gonzalez-Carro, S., Meir, P., and Sanchez, A.: Photosynthetic thermal acclimation capacity of tropical montane rainforest trees in Rwanda and in the Colombian Andes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-586, https://doi.org/10.5194/egusphere-egu23-586, 2023.

14:55–15:05
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EGU23-14858
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On-site presentation
Johan Uddling, Mirindi E. Dusenge, Aloysie Manishimwe, Olivier J. L. Manzi, Myriam Mujawamariya, Bonaventure Ntirugulirwa, Lasse Tarvainen, Maria Wittemann, Etienne Zibera, Donat Nsabimana, and Göran Wallin

The responses of tropical forests to climate change depends on the ability of trees to acclimate to warming, as well as how interspecific variation in these responses affect tree community composition. In a unique tropical elevation gradient experiment in Rwanda, Rwanda TREE, we examine the sensitivity of tropical trees and forest stands to warming and altered water supply. Mixed multi-species plantations (20 tree species, 1800 trees per site) have been established at three sites with large variation in elevation (1300-2400 m) and climate (17-24 °C mean daytime temperature), with additional water and nutrient manipulation treatments being applied at each site. Here we present an overview of results obtained this far regarding: (1) leaf gas exchange physiology; (2) photosynthetic heat tolerance; (3) water-use traits; (4) tree growth and mortality; (5) stand-level tree community composition. We also discuss the potential implications of our findings for the biodiversity and carbon storage of tropical forests in a changing climate.

How to cite: Uddling, J., Dusenge, M. E., Manishimwe, A., Manzi, O. J. L., Mujawamariya, M., Ntirugulirwa, B., Tarvainen, L., Wittemann, M., Zibera, E., Nsabimana, D., and Wallin, G.: Warming responses of tropical trees and forest stands explored in an elevation gradient experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14858, https://doi.org/10.5194/egusphere-egu23-14858, 2023.

15:05–15:15
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EGU23-11921
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ECS
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On-site presentation
Olivier Jean Leonce Manzi, Maria Wittemann, Myriam Mujawamariya, Aloysie Manishimwe, Jacques Habimana, Eric Mirindi Dusenge, Etienne Zibera, Lasse Tarvainen, Donat Nsabimana, Göran Wallin, and Johan Uddling

Current estimates of temperature effects on plants are usually based on air temperature (Tair), although it is well known that leaf temperature (Tleaf) can deviate considerably from Tair. In some studies, to overcome the problem of Tair often being a poor proxy of Tleaf, measurements of canopy temperature (Tcan) have been used instead. However, Tcan data do not capture the spatial variation in Tleaf among leaves with different thermoregulatory traits. This may be particularly problematic for highly diverse and heterogeneous tropical forest canopies. In this study, we used infrared thermometers to study Tleaf and Tcan in multispecies tropical tree plantations established at three sites along an elevation gradient from 2,400 m a.s.l. (17.1°C mean daytime temperature) to 1,300 m a.s.l. (24.0°C) in Rwanda.  Measurements of chlorophyll fluorescence were also conducted to study the photosynthetic heat tolerance of these species. Our results showed high Tleaf (up to ~50°C) and leaf-to-air temperature differences (ΔTleaf; on average 8-10°C and up to 24°C) of sun-exposed leaves. Both leaf size and stomatal conductance were important traits in controlling Tleaf. The Tleaf (and thus ΔTleaf) of sun-exposed leaves greatly exceeded the simultaneously measured values of Tcan (and ΔTcan). Photosynthetic heat tolerance partially acclimated to increased growth temperature; on average 0.31°C increase in heat tolerance per 1°C increase in growth temperature. Consequently, thermal safety margins were narrower for species at the warmer, lower-elevation sites. Our findings highlight the importance of leaf traits for leaf thermoregulation and show that monitoring of canopy temperature is not enough to capture the peak temperatures and heat stress experienced by individual leaves in diverse tropical forest canopies. They also suggest that tropical trees have limited abilities to thermally acclimate to increasing temperatures.

Keywords: Canopy temperature, elevation gradient, fluorescence, heat tolerance, leaf area, leaf temperature, stomatal conductance, thermoregulation, tropical forest.

How to cite: Manzi, O. J. L., Wittemann, M., Mujawamariya, M., Manishimwe, A., Habimana, J., Dusenge, E. M., Zibera, E., Tarvainen, L., Nsabimana, D., Wallin, G., and Uddling, J.: Trait-based, spatial, and temporal variation in leaf temperature of tropical trees., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11921, https://doi.org/10.5194/egusphere-egu23-11921, 2023.

15:15–15:25
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EGU23-12108
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ECS
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On-site presentation
Pascal D. Schneider, Arthur Gessler, and Benjamin D. Stocker
Acclimation of photosynthesis allows plants to adjust to seasonal environmental changes and gradual long-term changes of similar magnitude. However, current global photosynthesis models diverge in their representation of temperature acclimation. Here, we applied fundamental principles of acclimation to identify key processes for predicting the response of photosynthesis to global warming.
 
We investigated how the instantaneous temperature response of photosynthesis changes due to acclimation of the photosynthetic capacities (changes in base rates of carboxylation, electron transport and respiration), the stomatal response (sensitivity to changes in vapour pressure), and the enzymatic response (changes in the enzyme kinetics of carboxylation and electron transport). Using a dataset of gas exchange measurements from globally distributed sites, we compared predicted and observed relationships between prevalent growth temperature (Tgrowth) and the optimal temperature of photosynthesis (Topt), the photosynthesis rate at Topt (Aopt), and the temperature sensitivity (width of the temperature response curve, Tspan).
 
The observational data showed a significant linear increase of  Topt with Tgrowth (0.74 °C/°C) and no correlations between Tgrowth and Aopt, respectively Tspan. To accurately predict Topt, all acclimation processes were required (R2 = 0.74). Acclimation of the enzymatic response was a key driver but caused an underestimation of Topt in tropical climates. This underestimation was resolved through acclimation of the base rate of respiration and the stomatal sensitivity to vapour pressure changes. Both decreased with increasing Tgrowth, resulting in an upwards shift of Topt and accurate predictions in tropical climates. Additionally, acclimation of the photosynthetic capacities was necessary to avoid an otherwise falsely predicted increase of Aopt with Tgrowth. The model predicted a linear decrease of Tspan with Tgrowth, indicating an incomplete formulation for the acclimation of the enzymatic response.
 
Our results demonstrate that the thermal acclimation of Topt and Aopt is predictable from the environment across species and that global photosynthesis models should adopt acclimation of the photosynthetic capacities, stomatal sensitivity and enzymatic response to predict the response of photosynthesis to global warming accurately.

How to cite: Schneider, P. D., Gessler, A., and Stocker, B. D.: Photosynthesis acclimates to warming through predictable changes in photosynthetic capacities, stomatal sensitivity and enzyme kinetics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12108, https://doi.org/10.5194/egusphere-egu23-12108, 2023.

15:25–15:35
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EGU23-4761
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ECS
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On-site presentation
Zhengfei Guo, Christopher Still, Calvin Lee, Youngryel Ryu, Benjamin Blonder, Jing Wang, Timothy Bonebrake, Alice Hughes, Yan Li, Henry Yeung, Kun Zhang, Ying Law, Ziyu Lin, and Jin Wu

To what extent plants thermoregulate their canopy temperature (Tc) in response to environmental variability is a fundamental question in ecology, and influences accurate projections of plants' metabolic response and resilience to climate change. However, debate remains, with opinions ranging from no to moderate plant thermoregulation capacities. Traditionally, it has been hypothesized that if plant thermoregulation occurs (i.e. ‘limited homeothermy’ hypothesis holds): 1) Tc will change more slowly than Ta over time, leading the Tcvs. Ta regression slope < 1; 2) Tc is cooler than Ta when Ta exceeds some threshold, typically during high net radiation conditions (e.g. at midday). Here, with global datasets of Tc, air temperature (Ta), and other environmental and biotic variables from FLUXNET and satellites, we tested the ‘limited homeothermy’ hypothesis across global extratropics, including temporal and spatial dimensions.

 

Our results demonstrate that across daily to monthly timescales, over 80% of sites/ecosystems have Tcvs. Ta regression slopes≥1 or Tc>Ta around midday, which rejects the ‘limited homeothermy’ hypothesis. For those sites unsupporting the hypothesis, their Tc-Ta difference (ΔT) still exhibits considerable seasonality that is negatively, partially correlated with their canopy structure seasonality (as indicated by leaf area index), implying a certain degree of thermoregulation capability. Across global sites, both site-mean ΔT and slope indicator exhibit considerable spatial variability, with ΔT having greater variability than the slope indicator. Furthermore, this large spatial ΔT variation (0-6°C) can be mainly explained by environmental variables (38%) and, to a lesser extent, by biological factors (15%). Our results suggested that plant thermoregulation patterns are diverse across global extratropics, with most ecosystems rejecting the ‘limited homeothermy’ hypothesis, but their thermoregulation still occurs, implying that slope<1 or Tc<Ta are not necessary conditions for plant thermoregulation.

How to cite: Guo, Z., Still, C., Lee, C., Ryu, Y., Blonder, B., Wang, J., Bonebrake, T., Hughes, A., Li, Y., Yeung, H., Zhang, K., Law, Y., Lin, Z., and Wu, J.: Does plant ecosystem thermoregulation occur?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4761, https://doi.org/10.5194/egusphere-egu23-4761, 2023.

15:35–15:45
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EGU23-6641
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On-site presentation
Efstratios Bourtsoukidis, Andrea Pozzer, Jonathan Williams, David Makowski, Josep Peñuelas, Vasileios Matthaios, Theo Economou, Georgia Lazoglou, Ana Maria Yañez-Serrano, Anke Nölscher, Jos Lelieveld, Philippe Ciais, Mihalis Vrekoussis, Nikos Daskalakis, and Jean Sciare

The emission of mono- and sesquiterpenes from terrestrial vegetation plays a significant role in ecological interactions and atmospheric chemistry. Previous research has suggested that global emissions of these hydrocarbons are largely driven by responses to abiotic stress and can be simulated using a fixed exponential relationship (β coefficient) between different forest ecosystems and environmental conditions. However, our meta-analysis of published emission data (89 studies/835 β coefficients) reveals that the relationship between mono- and sesquiterpene emissions and temperature is more complex than previously thought. We have found that co-occurring environmental stresses can amplify the temperature sensitivity of monoterpene emissions, which is primarily related to the specific plant functional type (PFT). In contrast, the temperature sensitivity of sesquiterpene emissions decreases over the years. On average, warmer ecosystems appear more sensitive, indicating that plants adjust their emission rates in response to thermal stress. When a PFT-dependent β coefficient for monoterpenes was implemented in a biogenic emission model and coupled with a chemistry-climate model, it was found that atmospheric processes are highly sensitive to this coefficient and subject to amplified variations under rising temperatures.

How to cite: Bourtsoukidis, E., Pozzer, A., Williams, J., Makowski, D., Peñuelas, J., Matthaios, V., Economou, T., Lazoglou, G., Yañez-Serrano, A. M., Nölscher, A., Lelieveld, J., Ciais, P., Vrekoussis, M., Daskalakis, N., and Sciare, J.: The temperature sensitivity of mono- and sesquiterpene emissions from terrestrial vegetation: Insights from a meta-analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6641, https://doi.org/10.5194/egusphere-egu23-6641, 2023.

Coffee break
Chairpersons: Liz Hamilton, Johanna Pihlblad
16:15–16:20
16:20–16:40
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EGU23-8927
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solicited
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Highlight
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On-site presentation
Allan Buras, Benjamin Meyer, and Anja Rammig

According to climate projections, extreme summer drought conditions as those striking Central and Southern Europe in 2022 will become more frequent under climate change. Consequently, studying forests’ response to such extreme conditions may reveal important insights on how forests will cope with anticipated climate conditions. Of particular interest are questions related to forest-type specific drought sensitivities (e.g. broadleaved vs. coniferous, Mediterranean vs. temperate) and the existence of legacy effects from previous droughts (e.g. the extreme 2018 drought, see Buras et al 2020).

While many approaches exist to address these questions at local scale, satellite borne remote sensing offers the opportunity to tackle these topics at large scale. Here, the MODIS mission provides a valuable source of information due to a relatively long observational period since the year 2000 at sufficient spatial resolution (250 m x 250 m) and a high sampling frequency (daily images which are used to compute 16-day maximum value composites). In context of monitoring forests' response to environmental conditions, MODIS NDVI renders a frequently considered data source since it reflects canopy greenness and consequently mirrors – among others – early leaf coloration and senescence as direct responses of trees to extreme drought. Yet, MODIS NDVI time-series need to pass a multi-step processing chain to mask poor-quality pixels, remove remaining outliers, gap-fill, and finally apply a pixel-specific standardization to achieve relative measures of canopy greenness. The recently launched European Forest Condition (EFCM, Buras et al 2021) provides correspondingly processed data, which can be used to monitor forest canopy condition in Europe through space and time.

Here, we present first insights on the impact of the 2022 drought on European forest ecosystems based on the EFCM. Preliminary results indicate the drought 2022 to supersede previous droughts with regards to the spatial extent of severely affected pixels, thus breaking the former record from the 2018 drought (Buras et al 2020) just four years later. Our analyses suggest that legacy effects from previous years have contributed to this development. Moreover, we found different drought sensitivities of different forest types. In combination, these factors draw a complex picture of forests climate-change resilience, which we here seek to disentangle. Corresponding knowledge will likely provide valuable empirical information to improve model-based projections of tree-species performance under anticipated climate change.

Buras A, Rammig A and Zang C S 2020 Quantifying impacts of the 2018 drought on European ecosystems in comparison to 2003 Biogeosciences 17 1655–72

Buras A, Rammig A and Zang C S 2021 The European Forest Condition Monitor: Using Remotely Sensed Forest Greenness to Identify Hot Spots of Forest Decline Frontiers in Plant Science 12 2355

How to cite: Buras, A., Meyer, B., and Rammig, A.: Record reduction in European forest canopy greenness during the 2022 drought, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8927, https://doi.org/10.5194/egusphere-egu23-8927, 2023.

16:40–16:50
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EGU23-11381
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On-site presentation
Mana Gharun, Ankit Shekhar, and Nina Buchmann

The frequency and intensity of extreme climate events is increasing globally. In 2022, Europe experienced extreme heatwaves and prolonged droughts followed by clear indications of a devastating effect across many forest sites. Instrumental measurements show that 2022 contained some of the most extreme heat and dryness conditions ever recorded across Europe, particularly during the forest growing season. Such extreme conditions that follow a number of consecutive extreme years (e.g., 2019, 2018, 2015) with short intervals in between are becoming the new norm and the response of forests in terms of canopy condition, reduced productivity, and potential feedback to the climate is not clear. It is yet not clear how the negative and positive impacts of the most recent extreme temperature and dryness conditions differ from the impact of previous extreme conditions. This study aims to: 1) compare the severity of extreme conditions in 2022 (in terms of heat and dryness) with the preceding extreme years (i.e., 2003, 2015, 2018, 2019) and 2) to quantify forest canopy response (in terms of vegetation browning) and variables responsible for the feedback from forests to the climate (transpiration and solar induced fluorescence as a proxy for photosynthetic activity) across the main classes of forest types in Europe.

For this assessment we use spatially explicit daily modelled top soil water content (0-7 cm), air temperature, and potential transpiration using the ERA5-Land spatial dataset (0.1° × 0.1°) between 1970 to 2022. Reference period for anomaly assessment is set to the 1970-2000 period and MODIS land cover type product is used to aggregate anomalies across forest types. SIF anomalies are extracted using an OCO-2 satellite based SIF dataset, and ground-based ecophysiological measurements collected across a few sites during heatwave and drought events in 2022 are compiled and used to link leaf-level processes to observed canopy response.

Our initial assessment shows that conditions in July 2018 had the largest negative impact on transpiration of European forests, but in June 2022 we observed a far larger spatial extent of positive temperature anomalies across Europe. We compare the impact of 2022 extreme conditions with that of previous extreme years, and discuss our results in the light of underlying ecophysiological mechanisms that control the response and the feedback to climate across different forest types and climate regions.

How to cite: Gharun, M., Shekhar, A., and Buchmann, N.: Assessment of the impact of 2022 extreme climate conditions on European forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11381, https://doi.org/10.5194/egusphere-egu23-11381, 2023.

16:50–17:00
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EGU23-1802
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Highlight
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On-site presentation
Tamir Klein, Jose Torres-Ruiz, and John Albers

The unprecedented heatwave that hit the Pacific northwest of North America in late June-early July 2021 impacted ecosystems and communities, yet evidence and analysis of this impact are still missing. Here we bring a unique dataset quantifying the impact on conifer trees, which are keystone species of many northwest ecosystems. Moreover, we take advantage of this exceptional event as a broad, extreme, “field experiment” to test a fundamental theory in plant physiology, and prepare our forests to a harsher future. Overall, the data collected confirm the role of hydraulic vulnerability in drought-induced injury to trees. Among the recorded species, we obtained P50 data for 27 species, represented by 64 cultivars. Plotting needle browning extent by P50 revealed important thresholds of drought sensitivity: (1) species with P50 <-6 MPa were unaffected by drought. (2) species with -6 MPa< P50 <-5 MPa had mild extent of needle browning, up to 25% of the canopy. (3) species with P50 > -5 MPa had browning of up to 95%. The sharp divergence among resistant and vulnerable conifer species according to their xylem vulnerability, all of which simultaneously exposed trees to the same extreme event at the same site, is evidence to the key role of P50, in agreement with previous assessments of drought effects on angiosperms. Among local, NW conifer species, some cultivars proved hardier than others. The aftermath of the 2021 NW heatwave should take advantage of this broad, extreme, “field experiment” to prepare our forests to a harsher future.

How to cite: Klein, T., Torres-Ruiz, J., and Albers, J.: Conifer desiccation in the 2021 NW heatwave confirms the role of hydraulic damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1802, https://doi.org/10.5194/egusphere-egu23-1802, 2023.

17:00–17:10
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EGU23-6144
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ECS
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On-site presentation
Yixuan Wang, Yuanyuan Wang, Xiaoxiang Zhu, Anja Rammig, and Allan Buras

In recent decades, forests are increasingly suffering from so-called hotter droughts. This is because rising temperatures increase the atmospheric water demand under drought, thereby amplifying plant-water consumption. As a consequence, soil-water potentials are reaching more extreme values which eventually may result in xylem cavitation and possibly tree die-back. For instance, the extreme 2018 drought resulted in extraordinary die-back frequencies in numerous tree species across Central Europe such as European beech, Norway spruce, and Scots pine. Since forests render an important agent in terms of climate change mitigation, increasing forests' climate-change resilience via forest conversion is essential to preserve their integrity and consequently ecosystem services related to carbon sequestration.

 

In this context, better knowledge of species-specific drought responses is highly valuable since it allows for determining critical drought thresholds beyond which the functional integrity of trees is at threat. Such knowledge may serve to parameterize dynamic vegetation models, which then can be deployed to project tree-species-specific performance under various climate change scenarios. Eventually, this may guide forest managers to select more climate-resilient tree species portfolios in terms of forest conversion.

 

Yet, species-specific drought responses are typically derived from plot-based physiological monitoring networks. While this approach provides valuable and highly precise data on tree physiology and it suffers from a relatively low replication. To overcome this low-spatial replication, large-scale assessments using satellite-based remote sensing appear a promising research avenue. For instance, the recently released European forest condition monitor (EFCM) provides information on forest canopy conditions in near real-time, which was shown to successfully quantify drought impacts under previous droughts (Buras et al., 2020, 2021). However, the EFCM currently does not allow for species-specific assessments given a lack of corresponding data, in particular tree-species classifications.

 

To overcome this research gap and to deepen our knowledge of species-specific drought responses, we here present a machine-learning-based tree-species classification using Moderate Resolution Imaging Spectroradiometer (MODIS) of Germany which is subsequently used to stratify EFCM data to quantify the species-specific response of most abundant tree-species (in particular beech, oak, spruce, and pine) to the extreme 2022 drought. Preliminary results indicated a successful calibration-validation of the tree-species classification, with the corresponding F1-scores in the order of 0.55 – 0.7 and true-skill statistics in the order of 0.6 – 0.78, indicating average to good performance. Once applied to stratify the EFCM data we provide a well-replicated large-scale assessment of tree-species-specific drought response, which will improve our understanding of species-specific climate-change resilience. Corresponding information can then be used further to parameterize dynamic vegetation models, which eventually can be deployed to obtain projections of tree performance under various climate-change scenarios.

 

Buras A, Rammig A and Zang C S 2020 Quantifying impacts of the 2018 drought on European ecosystems in comparison to 2003 Biogeosciences 17 1655–72

Buras A, Rammig A and Zang C S 2021 The European Forest Condition Monitor: Using Remotely Sensed Forest Greenness to Identify Hot Spots of Forest Decline Frontiers in Plant Science 12 2355

How to cite: Wang, Y., Wang, Y., Zhu, X., Rammig, A., and Buras, A.: Quantifying Tree-species Specific Responses to the Extreme 2022 Drought in Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6144, https://doi.org/10.5194/egusphere-egu23-6144, 2023.

17:10–17:20
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EGU23-11752
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ECS
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On-site presentation
Xiaofei Liu, Jakob Heinzle, Ye Tian, Erika Salas, Steve Kwatcho-Kengdo, Werner Borken, Andreas Schindlbacher, and Wolfgang Wanek

Abstract: Climate warming poses major threats to temperate forests, but the response of plant root metabolism has remained unclear. Understanding and predicting the impact of climate warming on the root metabolome represents a grand challenge and a major opportunity to predict the belowground functioning of forests in a warmer climate. We here studied the impact of long-term soil warming (>14 years, ambient versus +4 °C) on the fine root metabolome across three seasons (spring, summer, and autumn) for two years in a spruce-dominated mountain forest in the Austrian Limestone Alps. Root primary metabolites were analyzed with a liquid chromatography-mass spectrometry metabolomics platform (LC-Orbitrap MS). A total of 44 primary metabolites were identified in roots (19 amino acids, 12 organic acids, and 13 sugars). Warming and season had significant effects on total primary metabolite concentration, but no interaction effect. Warming increased the amino acid and sugar concentrations but did not affect organic acids. This may be explained by increased activity of the protein amino acid (such as arginine, glycine, and lysine) biosynthesis and metabolism and/or of root carbohydrate metabolism and transport under warming. The non-metric multidimensional scaling (NMDS) showed that soil warming was not significantly affecting the primary metabolite profiles, but year and season had significant effects. Season impacted primary metabolite profiles through changing soil temperature and years by effects on the soil environment (soil temperature and soil moisture) and root morphology (root length, specific root area, specific root length, and root diameter). In addition, we found that the root metabolism activity in warmed plots was lower than in control plots at the same soil temperature. Our data indicated that root metabolism in long-term warmed soil undergoes thermal acclimation, which may help match root metabolism with the required nutrient uptake and assimilation.

Keywords: Soil warming, root metabolism, primary metabolites, temperate forest.

How to cite: Liu, X., Heinzle, J., Tian, Y., Salas, E., Kwatcho-Kengdo, S., Borken, W., Schindlbacher, A., and Wanek, W.: Long-term soil warming changes the quantity but not the composition of primary metabolites of tree fine roots, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11752, https://doi.org/10.5194/egusphere-egu23-11752, 2023.

17:20–17:30
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EGU23-16874
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ECS
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Highlight
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Virtual presentation
Zelalem Mekonnen and William Riley

A large amount of carbon is stored in global forests. However, the fraction of carbon stored as plant biomass vs. soil organic carbon (SOC) varies among forest types. The extent to which biomass and SOC pools may change over the 21st century is uncertain, yet important to carbon cycle interactions with climate change. Here, we used data derived from inventories and remote sensing and CMIP6 models to examine the current and 21st century dynamics in the proportion of biomass and SOC across global forests. Our results show contrasting ecosystem carbon pools of forests in colder vs. moist warmer climates. Boreal forests currently store only 14±7% of their ecosystem carbon as plant biomass compared to 50 ±18% for moist tropical forests. We found that annual precipitation, topography, soil, and wildfire were the primary controls of these differences in forest carbon pool fractions. Under the Shared Socioeconomic Pathway (SSP5-8.5) climate scenario, CMIP6 models project that the ratio of biomass to ecosystem carbon in global forests will increase across the 21st century, with the largest increases in boreal forests compared to moist tropical forests. Changes in forest ecosystem carbon pools resulting in greater biomass fraction will affect the surface energy balance, disturbance regime, wildfire fuel loads, and ecosystem carbon balances, all of which interact with the climate system.

How to cite: Mekonnen, Z. and Riley, W.: Impacts of climate warming on biomass proportion of global forest carbon stocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16874, https://doi.org/10.5194/egusphere-egu23-16874, 2023.

17:30–17:40
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EGU23-10187
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On-site presentation
Moonil Kim, Taejin Park, Youngjin Ko, Go-Mi Choi, and Woo-Kyun Lee

Forest biomass is used as a representative factor for forest size, forest maturity, and forest productivity, so quantitative evaluation is very important not only for management and harvest but also for the evaluation of ecosystem functions and services including CO2 absorption. The allometric equation is a method of estimating the value of each part through the relative growth rate of plants and is a methodology widely used from the past to the present. Recently, studies have shown that the relative growth system of trees is changing due to the increase in CO2 concentration in the atmosphere and the resulting climate change, raising the need to review the previously developed relative growth and coefficients. In this study, the height-DBH relative growth relationships of four major tree species in Korea [(Pinus densiflora (PD), Larix kaempferi (LK), Quercus variabilis (QV), and Quercus mongolica (QM)] were analyzed using the 5―7th NFI data. Furthermore, these results were compared with the present yield table from the national institute for forest science. As a result of the analysis, it was found that the expected height value for the same DBH increased as the NFI progresses. For example, as a result of model analysis, the expected height for PD, LK, QV, and QM for DBH 25cm were 12.48, 19.17, 14.47, and 13.19m in the 5th NFI data, respectively. From the 7th NFI data, they were estimated as 13.61 (+9.1%), 21.58 (+12.7%), 15.76 (+8.9%), and 13.93 m (+5.6%), respectively. These results indicate that the current growth of major tree species in South Korean forests is more active in height growth than in diameter growth under climate change when compared with the height-DBH development trends by tree species identified through past survey data.

How to cite: Kim, M., Park, T., Ko, Y., Choi, G.-M., and Lee, W.-K.: Changes in Tree height–diameter allometry for temperate forests: A large periodical observational study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10187, https://doi.org/10.5194/egusphere-egu23-10187, 2023.

17:40–17:50
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EGU23-13959
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ECS
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On-site presentation
Simon Jones and Peter Cox

The observed increase in forest productivity over the industrial period is largely attributed to a stimulation of photosynthesis by increasing atmospheric CO2 concentrations. The extent to which this fertilisation effect will persist in the future, however, is uncertain as competing limitations such as the availability of nutrients and soil moisture may prevent plants from making use of the carbon they assimilate, which may dominate the future photosynthesis response.

Many early studies of the CO2 fertilisation effect use simulations that make use of the classical ‘big-leaf’ approach for scaling leaf photosynthesis to the canopy described by Sellers et al., (1992), which has been shown to produce unrealistically low sensitivities to light. Light limitation has the potential to significantly weaken the CO2 fertilisation effect relative to these early predictions. More realistic multi-layer canopy schemes have since been developed that produce more accurate light responses, however, the impact that this has on predicted CO2 fertilisation seems to have gone unstudied.

In this presentation we present a modified version of the big-leaf canopy scheme. This new version produces more realistic sensitivities to light while remaining more computationally efficient than modern multi-layer canopy schemes. We examine the effect that the new big-leaf scheme has on predictions of future CO2 fertilisation and demonstrate the importance of correctly simulating the dominant limitations of photosynthesis.

How to cite: Jones, S. and Cox, P.: More realistic CO2 fertilisation in a revised big-leaf model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13959, https://doi.org/10.5194/egusphere-egu23-13959, 2023.

17:50–18:00
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EGU23-9675
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On-site presentation
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Li Li

Regional increases in atmospheric O3, mainly produced photochemically from anthropogenic precursor gases, have phytotoxicity due to its strong oxidizing properties. To determine the response of bamboo physiology to elevated O3 levels, three-year-old dwarf bamboo (Indocalamus decorus) clones were exposed to three O3 concentrations (Ambient-AA, 21.3 to 80.9 ppb in the daytime; AA+70, 70 ppb O3 above ambient; AA+140, 140 ppb O3 above ambient) in open-top chambers for one growing season in Beijing, China. Gas exchange, biomass, growth, soluble sugar, and starch contents were examined at the end of the experiment. Our findings indicated that: (1) elevated O3 treatments decreased the photosynthesis rate, total biomass, and bud numbers but increased individual bud biomass and rhizome bud to rhizome biomass ratio. The most severe reduction was observed in new rhizome biomass (35.9% reduction in AA+70 and 57.2%reduction in AA+140), whereas individual bud biomass increased by 50%and 75%in the AA+70
and AA+140 groups compared with AA, respectively; (2) the starch contents in the rhizome decreased by 28.4%, whereas soluble sugar increased by 38.1% in the AA+140 rhizome buds compared to AA; (3) only the culm numbers of pachymorph rhizomes (clumped) decreased, whereas no changes in leptomorph rhizomes were observed. However, the mean distance between two ramets was lengthened by 49.4% and 86.5% in AA+70 and AA+140, respectively. In conclusion, Indocalamus decorus allocated more nonstructural carbohydrates (NSCs) from the rhizome to the buds to form stronger buds and ensure the survival of newer generations as a high priority in response to O3 exposure. Indocalamus decorus may be conducive to escaping from disadvantaged habitats and decreasing resource competition by lengthening the distance between two ramets.

How to cite: Li, L.: Growth reduction and alteration of nonstructural carbohydrate (NSC)allocation in a sympodial bamboo (Indocalamus decorus) under atmospheric O3 enrichment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9675, https://doi.org/10.5194/egusphere-egu23-9675, 2023.

Posters on site: Mon, 24 Apr, 10:45–12:30 | Hall A

Chairpersons: L. M Mercado, Sophie Fauset, Johanna Pihlblad
A.221
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EGU23-4771
Mina Hong, Moonil Kim, Youngjin Ko, and Woo-Kyun Lee

Climate change is a global issue affecting our lives, surrounding environments, and socioeconomic sectors. Accordingly, the recently published IPCC sixth assessment report emphasizes the role of forests as a source of greenhouse gas sink and shows the importance of climate resilient development pathways (CRDPs). South Korea is also putting forth policies such as the ‘2030 NDC’ and ‘2050 LED’ and is trying to find sustainable forest management measures to respond to the new climate change regime. Therefore, this study sought strategic measures to solve problems such as age class imbalance and mortality increase due to climate change in forests using the Korean dynamic stand growth model. Furthermore, CRDP was selected through recently announced SSP climate data and policy-based forest management scenarios to respond to the new climate change regime. As a result, the climate scenario is SSP1, the forest management scenario is when clear-cut harvest according to the legal final cutting age and thinning is implemented about 200,000 ha, reforestation of appropriate species to respond to climate change, and access to the forest road is within 1km, it was found that the overall growth of the forest increased. Although the current growth of 4.3m3 ha-1 decreases to 2.39m3 ha-1 in 2050, it is predicted to increase to 3.16m3 ha-1 in 2100 through the growth of species suitable for the climate and balance of age classes. In addition, it was analyzed to contribute to the increase in sequestration and carbon storage in logs due to harvest. In conclusion, this study is meaningful in that it presents a future strategy for responding to the new climate regime by reflecting the environmental and ecological characteristics of South Korea.

 

How to cite: Hong, M., Kim, M., Ko, Y., and Lee, W.-K.: Forest management scenarios using Korean dynamic stand growth model considering the new climate change regime, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4771, https://doi.org/10.5194/egusphere-egu23-4771, 2023.

A.222
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EGU23-5932
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ECS
Kinga Kulesza and Agata Hościło

Forest ecosystem stress caused by climate change, in particularly prolonged and severe droughts, has already been manifested in several parts of Europe, including temperate and boreal forests. It is likely that droughts and heatwaves will occur more often, which might result in the ecological transition of the forests and loss of biodiversity. The assessment of climate change impact on forest ecosystems is complex, as response can vary in space (depending on the physiological vulnerability of ecosystems and site conditions), time, and among species (species resilience).

In this project we investigate the influence of several climatic variables (2 m temperature, rainfall, evapotranspiration and climatic water balance) on the forests condition in Poland in the period 2002-2021. To this end we use ERA-5 Land reanalysis data and vegetation indices – NDVI and EVI – derived from the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) – MOD13Q and MYD13Q. The remotely sensed indicators on vegetation consist of 8-day composites and have 250-m spatial resolution, while the climatic data is 0.1° x 0.1° spatial and 1-day temporal resolution.

The spatio-temporal trends of NDVI and EVI were computed for forest areas only, and their statistical significance was assessed. The monthly analyses were carried out for growing season (April-October). Multi-annual trends of climatic variables were prepared not only for the period 2002-2021, but also for the longer period 1971-2021, in order to strengthen the information coming from the climate trend analysis. The influence of the variability of climate elements on vegetation indices was assessed with the methods of linear regressions and spatial correlations. The results were broken down into sub-regions of similar physical-geographical features (nature-forest classification).

Identification of the relation between changing climate and forests condition seems crucial, because forests are the important element in the planetary energy balance and CO2 absorption. In Poland almost 30% of country area (9.2 million ha) is covered with forests, but such research have not been conducted so far.

How to cite: Kulesza, K. and Hościło, A.: Influence of climatic variables on forests condition in Poland in the period 2002-2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5932, https://doi.org/10.5194/egusphere-egu23-5932, 2023.

A.223
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EGU23-6833
Lina Mercado, Zorayda Restrepo, Sebastian Gonzalez-Caro, Iain Hartley, Juan Villegas Palacio, and Patrick Meir

Tropical forests are expected to be highly vulnerable to climate change. Observations from the tropical montane Andean forests report a change in composition towards a greater relative abundance of warm affiliated species, i.e thermophilic species. These shifts are hypothesised to result from differential responses to warming of cold- and warm-affiliated species, with the former experiencing mortality and the latter migrating upslope. However, the drivers of these changes are poorly understood. Along a 2000m altitudinal gradient/thermosequence in the Colombian Andes, we planted 2-yr old individuals of cold- and warm-affiliated species under common soil and water conditions, exposing them to the hot and cold extremes of their thermal niches, respectively. We show that cold-affiliated species growing outside and on the hotter portion of their thermal ranges decreased their growth. Warm-affiliated species can survive but reduce their growth under the colder portion of their thermal distribution. We demonstrate that growth responses are related to species’ thermal distributions; survival probability increased as species’ distribution optima were warmer than the experimental site and decreased as species’ distribution optima were colder than the study sites. These results can be explained by the negative effects of heat stress on simulated photosynthesis.  Our findings highlight the potential effects of rapid warming on the composition of highland forest species in this biodiversity hotspot.

How to cite: Mercado, L., Restrepo, Z., Gonzalez-Caro, S., Hartley, I., Villegas Palacio, J., and Meir, P.: High vulnerability of highland Andean forests to warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6833, https://doi.org/10.5194/egusphere-egu23-6833, 2023.

A.224
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EGU23-5561
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ECS
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Highlight
Kristian Schufft, Katrin Fleischer, Anja Rammig, Lin Yu, and Sönke Zaehle

Increased atmospheric carbon dioxide (CO2) is known to enhance  leaf-level photosynthesis. Following the carbon fertilization hypothesis, the increased photosynthetic assimilation may lead to an increase in plant biomass, therefore representing a negative feedback mechanism to rising CO2 emissions. The magnitude and limitations of this effect remain one of the major uncertainties in projecting the future influence of increasing atmospheric CO2 on terrestrial biogeochemical cycles and climate change.

Forests contribute strongly to the contemporary terrestrial carbon (C) sink, however, the magnitude of the effect of elevated carbon dioxide (eCO2) on these ecosystems is still not fully understood. While experiments have demonstrated that young forests show increased aboveground biomass production under eCO2, the evidence for the effect on mature forests is still ambiguous. In these ecosystems, enhanced translocation of additional assimilated C belowground instead of investing in aboveground structure may significantly reduce C accumulation due to enhanced photosynthesis. One key mechanism in this process is exudation of C via roots into soil, which can increase nutrient availability to plants but also leads to soil C losses. By using a terrestrial biosphere model (QUINCY), which comprises a representation of the coupled carbon-nitrogen-phosphorus cycles in terrestrial ecosystems, we simulate the effect of elevated CO2 on exudation and its consequences for the C cycling and storage in mature forests. In comparison to other existing models we calculate exudation rates dynamic, based on plant carbon surplus and nutrient demand. We evaluate the effect using alternative representations of soil biogeochemical processes at the example of the EucFACE experiment in a mature Eucalyptus forest. We show that nutrient-stress induced increases in the exudation rate under eCO2 partially explains higher soil respiration and therefore lower C accumulation in this forest ecosystem.

How to cite: Schufft, K., Fleischer, K., Rammig, A., Yu, L., and Zaehle, S.: Modeling the effect of elevated CO2 on root exudation and ecosystem carbon storage in mature forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5561, https://doi.org/10.5194/egusphere-egu23-5561, 2023.

A.225
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EGU23-17442
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ECS
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Calil Amaral, Emma Docherty, Emmanuel Gloor, and David Gailbraith

Ongoing global warming threatens to exceed the physiological limits of forests, especially in the tropics, where species operate close to their thermal limits of photosystems. Understanding the relationship between leaf temperature, climatic variables and functional traits is therefore essential to predict the impacts of warming on forest ecology. The climatic safety margins  can be defined as the range of climatic values within which a species in a given environment maintains its physiological functions without risk of severe damage that can ultimately lead to death and are typically computed as the difference between an operational variable of physiological tolerance (e.g. temperature that corresponds to a 50% drop in the quantum photosynthetic efficiency of photosystem II) and a variable of exposure to physiological stress (e.g. maximum leaf temperature). Here, we aim to understand how thermal safety margins vary in response to increased air temperature and water stress at multiple spatial and temporal scales and relate these to species-level functional traits. We present an unprecedented set of surface temperature data measured with Unmanned Aerial Vehicle (UAV) thermal imaging in long-term forest plots in regions subjected to strong seasonal drought and rising temperatures in the southern edge of the Amazon and also for a 20-year drought experiment in northern Amazonia. The data collected includes diurnal patterns of crown temperature collected with UAVs in the dry and wet seasons, climatic variables and functional traits related to thermal and hydraulic tolerance. We examine seasonal variations in canopy temperatures and thermal safety margins and evaluate the extent to which these vary according to canopy structure, leaf size, soil properties and soil moisture availability. Our data provides insights into leaf resilience to warming and factors controlling leaf temperatures in tropical forests. Our results will ultimately help indicate which forest types and species will be better able to cope with future temperature increases.

How to cite: Amaral, C., Docherty, E., Gloor, E., and Gailbraith, D.: Integrating UAV thermal individual-based images and functional traits to investigate thermal sensitivity of Amazonian forestsE, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17442, https://doi.org/10.5194/egusphere-egu23-17442, 2023.

A.226
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EGU23-14149
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ECS
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Hye In Yang, Marion Schrumpf, and Sönke Zaehle

Elevated atmospheric carbon dioxide (CO2) concentrations can have a positive effect on plant growth, and are also expected to alter the plant belowground allocation of photosynthetically fixed carbon (C). The release of root-derived exudates can potentially stimulate soil microbial activity and the turnover of existing soil C. However, soil organic matter decomposition response to elevated CO2 may vary depending on the level of available nutrients, particularly nitrogen (N), which is the most limiting nutrient. To investigate the combined effect of COand available N on rhizodeposition and soil C turnover, a greenhouse mesocosm experiment was conducted. A total of 64 hornbeam (Carpinus betulus L.) trees were exposed to ambient (400 ppm, aCO2) or elevated (580 ppm, eCO2) concentrations of CO2 at 13C-enrichment of 100 permil, in order to trace C in the system. Two levels of N were applied to the soils in the form of 15N-labelled ammonium nitrate (NH4NO3). Above and belowground C fluxes were continuously monitored for partitioning of soil heterotrophic and autotrophic respirations. After one growing season, the trees and soils were destructively harvested. The trees were separated into buds, leaves, branches, stem and roots, which were analysed for CN and their respective isotopic compositions. Soils were separated into rhizosphere and bulk soils, and were analysed for CN, isotopic compositions, microbial biomass and enzyme activities. We observed an increase in the belowground C allocation under eCO2 and trees showed a higher active fine root growth response to eCO2. Consequently, the overall microbial biomass in the rhizosphere as well as the fraction of microbial biomass C derived from roots increased under eCO2. Enzyme activities, especially those of β-Glucosidase and N-acetyl-β-d-glucosaminidase, increased, while phosphatase and peroxidase activities decreased under eCO2. Despite the stimulated microbial activities, changes in soil C were not observed. Furthermore, we did not find any interactive effect of available N with eCO2, which suggested that N availability did not strongly influence belowground C allocation by trees.

How to cite: Yang, H. I., Schrumpf, M., and Zaehle, S.: Effect of elevated CO2 and soil nitrogen availability on plant C allocation and soil C turnover from a whole-plant mesocosm experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14149, https://doi.org/10.5194/egusphere-egu23-14149, 2023.

A.227
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EGU23-17522
Sukyoung Kim, Jaeyeon Choi, and Chan Park

Under Paris Agreement, carbon sink at the national level has been reported to the international community. There are various attempts to improve the accuracy of reporting on the national carbon sink. Especially, IPCC has discussed the necessity of reports distinguished by artificial and natural factors’ effects on the carbon sink based on the Interannual variability (IAV) (IPCC, 2019). However, there are no clear methods to identify the effect of artificial factors. The forest, which has a high density of vegetation, is important as the place that absorbs carbon. The accelerated photosynthesis process of forests by climate change can lead to changes in vegetation productivity and carbon sink. Forest net primary productivity is representative of carbon sink in vegetation which retains the amount of carbon based on aboveground biomass.

The main purpose of this study is to suggest a method to extract climate-driven changes in the carbon sink of forest ecosystems in order to increase the accuracy of carbon sink reported to the international community. The suggested method is composed of three steps: 1) This study estimated annual forest net primary productivity change due to climate change using the Carnegie-Ames-Stanford Approach (CASA) model. 2) The variability of FPAR and temperature affected by climate change was extracted through the Empirical mode decomposition (EMD) algorithm, which decomposes a time-series signal. Then, this value was applied to the CASA model to estimate the change in the net primary production of forest ecosystems. 3) The forest productivity due to the climate effect was derived by comparing the above two results.

This assessment approach is expected to understand the variability of forest carbon sink and to support the decision-making of the greenhouse gas reduction report system by assessing climate-driven changes in forest net primary productivity.

How to cite: Kim, S., Choi, J., and Park, C.: Detecting Climate-Driven Increases in Interannual Net Primary Productivity of Forest Ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17522, https://doi.org/10.5194/egusphere-egu23-17522, 2023.

A.228
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EGU23-12072
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ECS
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Angeliki Kourmouli, Liz Hamilton, Rebecca Bartlett, Rosemary Dyson, James Gore, Robert Grzesik, Iain Hartley, Iain Johnston, Alexandra Kulawska, Carolina Mayoral, Susan Quick, Michaela Reay, Zongbo Shi, Andy Smith, Sami Ullah, Clare Ziegler, and A. Rob Mackenzie

Anthropogenic CO2 emissions have resulted in elevated CO2 (eCO2) in the atmosphere, and this rise is predicted to continue1. Increases in CO2 have fertilised forest ecosystems and led to an uptake of CO2 into plant and soil biomass. Early findings at BIFoR FACE (Free-Air Carbon Dioxide Enrichment) showed increased photosynthetic uptake2, fine root net primary productivity3 and soil respiration4, indicating increased carbon (C) allocation belowground and mirroring previous forest FACE experiments. Roots play a key role in whole-plant functions, biogeochemical cycling and interactions with biotic factors, thus based on the early findings we expect that the increased C allocation belowground will have an impact on root biomass and architecture. Root biomass combined with root architecture (such as root diameter and length) are of high importance to elucidate the impacts of eCO2 on primary productivity, interactions in the rhizosphere, carbon sequestration and nutrient cycling5,6. This study assesses the impact of elevated CO2 on root biomass and architecture at the BIFoR FACE the first 5 years of operation (2017-2022). 

 

Changes in root biomass and architecture were monitored via soil coring three times a year (spring, summer and autumn) to 30 cm (per horizon). The root biomass in assessed as per dry weight in four different root diameter classes (<1, 1-2, 2-5 and >5 mm) and the root architecture was assessed via fresh root scanning.

 

Root biomass exhibited a prompt and sustained increase under eCO2 during the first 5 years of CO2 fumigation, with the increase being more pronounced for the three smaller diameter classes (<1, 1-2 and 2-5 mm). Moreover, the increase was relatively higher in the O and B soil horizons. Due to limited abundance of larger roots in the top soil layers, no clear patterns have been observed for the largest root class (>5 mm). Increases in root biomass could suggest increases in total root length, root diameter and tissue density, enhancing trees’ capacity to acquire more soil resources such as water and nutrients, or resource storage.

 

References

1Intergovernmental Panel on Climate Change; Core Writing Team; Pachauri, R.K.; Meyer, L.A. (Eds.) Climate Change 2014: Synthesis Report, Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change; Intergovernmental Panel on Climate Change: Geneva, Switzerland, 2014; 151p.

2Gardner, A., Ellsworth, D., Crous, K., Pritchard, J., Mackenzie, A.R. (2021). Is photosynthetic enhancement sustained through three years of elevated CO2 exposure in 175-year-old Quercus robur? Tree Physiology, 42 (1), 130-144

3Ziegler, C., Kulawska, A., Kourmouli, A., Hamilton, L., Shi, Z., MacKenzie, A.R., Dyson, R.J., Johnston, I.G. (2022). Quantification and uncertainty of root growth stimulation by elevated CO2 in mature temperate deciduous forest. Science of the Total Environment, 854,

4Kourmouli, A., Hamilton, L., Pihlblad, J., Barba, J., Bartlett, R., MacKenzie, AR., Hartley, I., Shi, Z. (2023). Initial carbon and nutrient responses to free air CO2 enrichment in a mature deciduous woodland. (submitted)

5Norby, R. J., & Jackson, R. B. (2000). Root dynamics and global change: Seeking an ecosystem perspective. New Phytologist, 147, 3–12.

6Wilson, S. D. (2014). Below-ground opportunities in vegetation science. Journal of Vegetation Science, 25, 1117–1125.

How to cite: Kourmouli, A., Hamilton, L., Bartlett, R., Dyson, R., Gore, J., Grzesik, R., Hartley, I., Johnston, I., Kulawska, A., Mayoral, C., Quick, S., Reay, M., Shi, Z., Smith, A., Ullah, S., Ziegler, C., and Mackenzie, A. R.: Does elevated CO2 alter root architecture and biomass after 5 years in a mature temperate woodland?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12072, https://doi.org/10.5194/egusphere-egu23-12072, 2023.

5 min introduction

Posters virtual: Mon, 24 Apr, 10:45–12:30 | vHall BG

Chairpersons: L. M Mercado, Sophie Fauset
vBG.12
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EGU23-14587
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ECS
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Ugo Molteni, Arun Bose, Celia Faiola, Jonan Gisler, Shan Gu, Stefan Hunziker, Markus Kalberer, Na Luo, Tatiana Nazarova, Simone Maria Pieber, and Arthur Gessler

Biogenic volatile organic compounds (BVOCs) comprise the largest, most highly complex, and diverse fraction of the volatile organic compounds (VOCs) emitted into the atmosphere (Sindelarova et al., 2014). By emitting BVOCs, plants communicate, fight herbivores and attract pollinators (Niinemets and Monson, 2013). Atmospheric oxidation of BVOCs affects the concentration of methane, carbon monoxide, and tropospheric ozone and leads to the formation of Secondary Organic Aerosol (SOA). Atmospheric aerosol load plays a crucial role in defining the radiative balance and negatively impacts air-quality standards (Seinfeld, John H. and Pandis, Spyros N., 2016). 

Climate models project an increase in the average global temperature for the next decades, with Alpine regions expected to be over-proportionally more affected. Drought, heat, and insects feeding on plants cause stress in the organism, which the organism reacts to by changing the BVOCs emissions: certain compounds can be promoted, and others reduced. This may lead to subsequent changes in atmospheric chemistry and SOA properties depending on the cause of stress and the plant’s reaction (Smith et al., 2021). 

Within the experimental project "Acclimation and environmental memory” in 2022, we studied the impact of prolonged heat and drought on BVOC emission from Scots pine (Pinus Sylvestris) seedlings. Seedlings were grown from seeds collected from selected mother trees from the long-term irrigation experiment Pfynwald, with different long-term water availability. This allowed us also to examine the additional consequence of transgenerational memory on BVOC emissions (Bose et al., 2020). Our results combine data from samples collected on sorbent tubes and analyzed by Thermal Desorption GC-MS with online BVOC measurements using  PTR-ToF-MS and provide a well-resolved picture of terpene compositions as well as diurnal trends in emission levels.

 

Bibliography 

Bose, A. K., Moser, B., Rigling, A., Lehmann, M. M., Milcu, A., Peter, M., Rellstab, C., Wohlgemuth, T., and Gessler, A.: Memory of environmental conditions across generations affects the acclimation potential of scots pine, Plant Cell Environ., 43, 1288–1299, https://doi.org/10.1111/pce.13729, 2020.

Niinemets, Ü. and Monson, R. K. (Eds.): Biology, Controls and Models of Tree Volatile Organic Compound Emissions, Springer Netherlands, Dordrecht, https://doi.org/10.1007/978-94-007-6606-8, 2013.

Seinfeld, John H. and Pandis, Spyros N.: Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 3rd Edition., Wiley, 1152 pp., 2016.

Sindelarova, K., Granier, C., Bouarar, I., Guenther, A., Tilmes, S., Stavrakou, T., Müller, J.-F., Kuhn, U., Stefani, P., and Knorr, W.: Global data set of biogenic VOC emissions calculated by the MEGAN model over the last 30 years, Atmospheric Chem. Phys., 14, 9317–9341, https://doi.org/10.5194/acp-14-9317-2014, 2014.

Smith, N. R., Crescenzo, G. V., Huang, Y., Hettiyadura, A. P. S., Siemens, K., Li, Y., Faiola, C. L., Laskin, A., Shiraiwa, M., Bertram, A. K., and Nizkorodov, S. A.: Viscosity and liquid–liquid phase separation in healthy and stressed plant SOA, Environ. Sci. Atmospheres, 1, 140–153, https://doi.org/10.1039/D0EA00020E, 2021.

How to cite: Molteni, U., Bose, A., Faiola, C., Gisler, J., Gu, S., Hunziker, S., Kalberer, M., Luo, N., Nazarova, T., Pieber, S. M., and Gessler, A.: Biogenic volatile organic compound emissions from Scots pine seedlings under prolonged heat and drought, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14587, https://doi.org/10.5194/egusphere-egu23-14587, 2023.

vBG.13
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EGU23-16015
Rebecca Oliver, Lina Mercado, Doug Clark, Phil Harris, and Belinda Medlyn

A key driver of the terrestrial carbon sink is photosynthesis. Accurate representation of this process in Earth System models is important to help understand and quantify the resilience of the global carbon sink to future climate change. In the JULES land surface model (the land surface component of the UK Earth System model - UKESM), we implement thermal adaptation and acclimation of photosynthesis using the latest scheme from Kumarathunge et al., (2019), which is based on data from 141 C3 species covering a diverse range of biomes from tropical rainforest to arctic tundra. Additionally, we explore the sensitivity of photosynthetic acclimation to rising atmospheric CO2 concentrations. In model simulations using forcing based on RCP8.5 to explore the model response to increasing temperatures, we show that thermal adaptation and acclimation has a positive effect on GPP that persists to 2050, but the size of the response diminishes over time. Broken down by biome, this effect is most notable in the tropics. Additionally, opposite effects of temperature adaptation and acclimation are seen in tropical (adaptation effect decreases GPP over time, whereas acclimation increases GPP) versus temperate and boreal regions (adaptation effect is constant, whereas acclimation decreases GPP over time). The attenuation of the adaptation effect in the tropics is because high temperatures in this region cause a shift in the Jmax:Vcmax ratio such that photosynthesis becomes light-limited earlier (in contrast to simulations where thermal adaptation and acclimation is not activated). The light-limited rate of photosynthesis is less sensitive to increasing atmospheric CO2 concentrations, therefore photosynthetic rates are reduced. This effect is not seen in the temperate/boreal regions because of the cooler temperatures here. Thermal acclimation results in seasonal shifts in the optimum temperature for photosynthesis. In the tropics, the optimum temperature for photosynthesis increases compared to control simulations without acclimation allowing for higher photosynthetic rates at leaf temperatures around the optimum. This increases the resilience of tropical vegetation to higher temperatures and heat extremes. In the temperate and boreal region, thermal acclimation lowers the optimum temperature for photosynthesis to adjust photosynthetic capacity to cooler spring temperatures. Acclimation of the Jmax:Vcmax ratio to increasing atmospheric CO2 concentration results in large decreases in GPP as CO2 concentrations rise across all biomes. Enabling thermal adaptation and acclimation in the JULES land surface model therefore leads to a lower CO2 fertilisation response of tropical vegetation as photosynthesis transitions from CO2-limited to light-limited earlier, however vegetation productivity benefits from adjustment of its thermal sensitivity of photosynthesis to local temperatures.

How to cite: Oliver, R., Mercado, L., Clark, D., Harris, P., and Medlyn, B.: The future of forests: thermal acclimation in the JULES land surface model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16015, https://doi.org/10.5194/egusphere-egu23-16015, 2023.

vBG.14
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EGU23-15088
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ECS
Simone M. Pieber, Ugo Molteni, Na Luo, Markus Kalberer, Celia Faiola, and Arthur Gessler

Biogenic volatile organic compounds (BVOCs) are a highly complex and diverse set of chemicals emitted into the atmosphere by the Earth's biosphere [1]. Atmospheric oxidation of BVOCs affects atmospheric mixing ratios of CH4, CO, and tropospheric O3, and leads to the formation of Secondary Organic Aerosol (SOA) (i.e., submicron particulate matter). Atmospheric aerosol plays a crucial role in defining Earth's radiative balance and impacts air-quality [2]. Climate models project a further increase in the average global temperature for the next decades. Warm winters appear to lead to earlier leaf-out which may put trees at higher risks of late frost in spring and summer droughts are increasing in frequency and extent. The probability that a late frost and an extreme summer drought occurs in the same year is expected to increase and thus, how trees respond to and recover from the (double) stress will be important in determining changes in BVOC emissions composition and quantities. Climate warming may thus lead to changes in atmospheric chemistry, including SOA properties [3]. During 2022, we studied the impact of spring frost and summer drought on BVOC emissions from broadleaf seedlings. We exposed 2-year-old seedlings of 3 species (Quercus petraea, Quercus robur, Fagus sylvatica) to an artificial spring frost by keeping seedlings with leaves that were fully out at -5.5℃ for 3 hours at the beginning of May 2022. Subsequently we simulated a summer drought from early July through the end of August (50% water reduction). The BVOC emissions of QP, QR, and FS, were measured deploying a PTR-ToF-MS alongside a newly developed plant chamber system [4] in August 2022.

We address the following research questions in our conference contribution: 

  • How do BVOC emissions composition and quantities of broadleaf control trees (QP, QR, FS) compare to coniferous ones (studied during AccliMemo 2022 [4])?
  • How are the BVOC emissions of QP and FS modulated in response to a) late spring frost, b) summer drought,  and c) double stress?

 

References:

[1] Sindelarova et al. Global data set of biogenic VOC emissions calculated by the MEGAN model over the last 30 years, ACP, 14, 9317–9341, https://doi.org/10.5194/acp-14-9317-2014, 2014

[2] Seinfeld, John H. and Pandis, Spyros N.: Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 3rd Edition., Wiley, 1152 pp., 2016

[3] Smith, N. R. et al.: Viscosity and liquid–liquid phase separation in healthy and stressed plant SOA, Environ. Atmospheres, 1, 140–153, https://doi.org/10.1039/D0EA00020E, 2021

[4] Molteni, U. et al., 2023, EGU23 GA Abstract Nr. EGU23-14587

 

Acknowledgements:

SMP acknowledges funding by the Swiss National Science Foundation (SNSF) grant no. P400P2_194390.

How to cite: Pieber, S. M., Molteni, U., Luo, N., Kalberer, M., Faiola, C., and Gessler, A.: Biogenic volatile organic compounds emitted by European Temperate forests: How do broadleaf species react to frost and drought?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15088, https://doi.org/10.5194/egusphere-egu23-15088, 2023.