BG3.15 | Terrestrial ecosystem responses to global change: integrating experiments, ecosystem observations, and models to understand carbon, nutrient, and water cycling
EDI
Terrestrial ecosystem responses to global change: integrating experiments, ecosystem observations, and models to understand carbon, nutrient, and water cycling
Convener: Benjamin Stocker | Co-conveners: Teresa Gimeno, Karin Rebel, Sönke Zaehle
Orals
| Wed, 26 Apr, 08:30–10:00 (CEST), 10:45–12:25 (CEST)
 
Room C
Posters on site
| Attendance Fri, 28 Apr, 14:00–15:45 (CEST)
 
Hall A
Orals |
Wed, 08:30
Fri, 14:00
Human activities are altering a range of environmental conditions, including atmospheric CO2 concentration, climate, and nutrient inputs. However, understanding and predicting their combined impacts on ecosystem structure and functioning and biogeochemical cycles is challenging. Divergent future projections of terrestrial ecosystem models reveal uncertainties about fundamental processes and missing observational constraints. Models are routinely tested and calibrated against data from ecosystem flux measurements, remote sensing, atmospheric inversions and ecosystem inventories. However, it remains challenging to use available observations to constrain process representations and parameterizations in models simulating the response of ecophysiological, biogeochemical, and hydrological processes to environmental changes.

This session focuses on the influence of CO2, temperature, water stress, and nutrients on ecosystem functioning and structure. A focus is set on learning from experiments and novel uses of continuous ecosystem monitoring and Earth observation data for informing theory and ecosystem models. Contributions may cover a range of scales and scopes, including plant ecophysiology, soil organic matter dynamics, soil microbial activity, nutrient cycling, plant-soil interactions, or ecosystem dynamics.

Orals: Wed, 26 Apr | Room C

Chairpersons: Teresa Gimeno, Sönke Zaehle
08:30–08:40
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EGU23-3712
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ECS
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Highlight
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On-site presentation
Mingkai Jiang, Belinda Medlyn, David Wårlind, Jürgen Knauer, Daniel Goll, Lin Yu, Katrin Fleischer, Haicheng Zhang, Xiaojuan Yang, Sönke Zaehle, David Ellsworth, and Benjamin Smith

The importance of phosphorus (P) in plant function and ecosystem biogeochemistry has led to the addition of a P cycle to a range of vegetation models, but the predictions of these P-enabled models have rarely been evaluated with ecosystem-scale data. Here, we confronted eight state-of-the-art, P-enabled models with data from EucFACE, a P-limited Eucalyptus forest subject to long-term Free-Air CO2 Enrichment. We evaluated the capability of the models to capture the observed elevated CO2 responses in this ecosystem. We show that the inclusion of phosphorus-cycle is necessary to more realistically simulate ecosystem function and biogeochemistry, but this enhanced capacity did not directly translate into improved prediction accuracy. Specifically, models diverged in capturing the observed CO2 responses, with simulation accuracy depending upon model assumptions about plant physiology, allocation, plant-soil interactions and soil nutrient processes. Confronting models with experimental responses observed at EucFACE represents a valuable opportunity to improve our understanding of the carbon-phosphorus interaction under rising CO2, and is an important step towards more accurate predictions of the future land carbon sink under climate change.

How to cite: Jiang, M., Medlyn, B., Wårlind, D., Knauer, J., Goll, D., Yu, L., Fleischer, K., Zhang, H., Yang, X., Zaehle, S., Ellsworth, D., and Smith, B.: Confronting models with data: carbon-phosphorus interaction under elevated CO2 in a mature forest ecosystem (EucFACE), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3712, https://doi.org/10.5194/egusphere-egu23-3712, 2023.

08:40–08:50
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EGU23-15918
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On-site presentation
Michael Bahn, David Reinthaler, Hans-Peter Piepho, Erich Pötsch, Andreas Schaumberger, Markus Herndl, Kathiravan Meeran, Rüdiger Kaufmann, Jesse Radolinski, and Maud Tissink and the ClimGrass-Team

In a future world, ecosystems will be affected by a concomitant increase in atmospheric CO2 concentrations, temperature and drought events. While the individual effects of elevated CO2, warming and drought on plant and ecosystem productivity are comparatively well understood, there is a major lack of experimental studies testing for their interactive effects. In a multifactor experiment (ClimGrass) established in 2013 on a managed montane grassland in Central Austria we tested how elevated CO2 (eCO2), warming (eT) and drought individually and interactively affect productivity and tissue stoichiometry.

Treatment effects varied and amplified across the eight treatment years, partly related to shifts in species composition. Above-ground net primary productivity (ANPP) was generally increased when eT and eCO2 were combined, while it was not consistently affected by the individual treatments. Drought and drought recovery effects on ANPP, gross primary productivity (GPP) and belowground carbon allocation were amplified when drought was combined with eT and eCO2. Both under current and future (eT, eCO2) scenarios drought altered tissue stoichiometry by decreasing phosphorus concentrations during drought and increasing nitrogen and potassium concentrations post-drought. Overall, our study suggests that in the temperate grassland studied drought had an overriding effect on productivity and tissue stoichiometry, which was amplified by warming, but only weakly altered by elevated CO2

How to cite: Bahn, M., Reinthaler, D., Piepho, H.-P., Pötsch, E., Schaumberger, A., Herndl, M., Meeran, K., Kaufmann, R., Radolinski, J., and Tissink, M. and the ClimGrass-Team: Individual versus combined effects of elevated CO2, warming and drought on grassland productivity and stoichiometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15918, https://doi.org/10.5194/egusphere-egu23-15918, 2023.

08:50–09:00
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EGU23-3858
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On-site presentation
Marta Galvagno, Ludovica Oddi, Edoardo Cremonese, Gianluca Filippa, Mirco Migliavacca, and Georg Wohlfahrt

Both natural and managed ecosystems contribute to mitigating climate change through the process of CO2 sequestration from the atmosphere. However, projections of future global climate indicate that extreme weather events will become more frequent and more intense in the coming years. And since heat waves and droughts can alter the ecosystems functioning, and increase the vulnerability of carbon sinks, this trend represents a potential risk for their contribution to reaching global climate change mitigation goals. Further efforts are therefore needed to assess the resistance and resilience of different ecosystems and land uses to climate change. In this context, Alpine mountain ecosystems face a double challenge, on the one hand, warming in the Alps is occurring twice as fast as in other regions of the planet and drought events are increasingly frequent, on the other, socio-economic changes have led to partial land abandonment, with effects on the composition and distribution of plant species.

The main objective of this study is to analyze the impacts of extreme heat and drought events on the functioning of two different ecosystems in the Alps, a European larch forest (Larix decidua Mill.) and an abandoned subalpine pasture dominated by Nardus stricta, both located in the Aosta Valley region (Italy) at about 2100 m asl and thus experiencing the same climate conditions. The eddy covariance method was used to measure the carbon and water fluxes between the ecosystem and the atmosphere. Radiometric vegetation indices (eg. NDVI), and field observations related to plant phenology were used to explain the role of timing in determining the carbon and water fluxes impacts. Finally, functional traits of plant species were used to interpret the divergent ecosystem responses from an adaptive perspective. The results show that the different heat and drought events observed during the ten-year study period (2012-2022) had a variable impact on the different ecosystems monitored, also based on the timing of the extreme event in relation to the phenology of the vegetation and the presence/absence of the snowpack, with impacts generally more severe for the grassland compared to the forest. The contrasting responses observed will be discussed by exploring the linkage between the functioning of the whole ecosystem and the adaptive strategies of individual plant species.

How to cite: Galvagno, M., Oddi, L., Cremonese, E., Filippa, G., Migliavacca, M., and Wohlfahrt, G.: Divergent responses of mountain forests and grasslands to heat and drought events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3858, https://doi.org/10.5194/egusphere-egu23-3858, 2023.

09:00–09:10
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EGU23-11200
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ECS
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On-site presentation
Nine Douwes Dekker, Elise Pendall, Liz Hamilton, Josep Barba, Johanna Pihlblad, Robert Mackenzie, Angeliki Kourmouli, Sirwan Yamulki, Vincent Gauci, and Sami Ullah

In this research we consider the response of soil respiration under elevated CO2 (eCO2) in an oak-dominated temperate forest. We hypothesised that under elevated CO2 (550 ppm) soil moisture would increase as a result of reduced stomatal conductance, which would in turn lead to higher soil respiration. Continuous measurements were performed on three pairs of plots near Stafford (United Kingdom). Respiration was measured diurnally for 2 minutes each time, using the LI-COR 8100A set-up, and the rate of respiration (flux rate) was calculated SoilFluxPro software. Next, an empirical model was fitted to the dataset based on hourly averages of the flux rates, soil temperature, and soil moisture. Three respiration collars per plot were averaged, thus accounting for spatial variability within the site. Model parameterization and gap filling were conducted on individual plots to calculate annual rates for 2019-2021. Cross-validation was performed by using 80% (randomly selected) of each dataset for training and the remaining 20% for testing the data against the parameters obtained by the empirical models. Preliminary results suggest that annual respiration rates were significantly higher for the eCO2 across all pairs in 2019. However, 2 out of 3 pairs in 2020 and 2021 showed significantly higher respiration for the aCO2 plots compared to eCO2, which is not in line with our hypothesis. Relationships with soil moisture and temperature help to explain what drives the difference in these fluxes. Our findings show that the relationship between higher CO2 concentrations in the atmosphere and soil respiration is not a straightforward one, which is of interest when considering the role of forest C-cycling on a global scale.

How to cite: Douwes Dekker, N., Pendall, E., Hamilton, L., Barba, J., Pihlblad, J., Mackenzie, R., Kourmouli, A., Yamulki, S., Gauci, V., and Ullah, S.: Inter-annual variability in the response of soil respiration to elevated CO2 concentrations in the atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11200, https://doi.org/10.5194/egusphere-egu23-11200, 2023.

09:10–09:20
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EGU23-14993
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ECS
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On-site presentation
Mar Albert-Saiz, Marcin Strozecki, Anshu Rastogi, and Radoslaw Juszczak

The global carbon cycle is highly affected by peatlands as they accumulate up to 40% of the soil carbon (C) stored globally. Gross primary productivity (GPP) is a key driver of this accumulation, it determines the amount of atmospheric CO2 sequestered into biomass. One of the most widespread techniques to measure CO2 exchange with the atmosphere are closed-chamber method, however, this technique is limited to small-scale studies and is dependent on spatial and temporal interpolations. A multi-model approach combining a water table depth (WTD) based model, classic rectangular hyperbolic (RH) models, modified RH models with temperature factors and an exponential model is used to study the effect of climate manipulation in a temperate peatland, selecting in each timestep the best model based on the Akaike Information Criterion corrected, p-value, root mean square error (RMSE) and R2 results.

Climatic conditions are changing rapidly, affecting the peatlands’ capability to sequester and store C, enhancing decomposition and changing vegetation cover and performance. Temperature and precipitation highly impact vegetation performance inducing stress, which is why climate manipulation experiments have increased over time following our concerns about climate change. The effect of temperature on vegetation productivity under warming and reduced precipitation conditions was observed after 3 years of climate manipulation in a temperate peatland. As shown by the partial least-squares regression while during the first year, the variance of GPP explained by temperature was 51% and 59% respectively, it increased to 73% for warming (W) and warming plus reduced precipitation (WP) sites and equally, the correlation between temperature and GPP rose from -0.81 (W) and -0.76 (WP) to -0.85. Additionally, when the annual average values of WTD increased from -19.3 ± 7.4 cm in 2018 to -16.7 ± 6.8 cm in 2021, the effect of 15-day average WTD oscillations in vegetation productivity became minor, from 63% of GPP variance explained by WTD to just 18% as more water was available. The effects are also visible in GPP annual cumulative values, increasing from -671 g CO2-C m-2y-1 and -672 g CO2-C m-2 y-1 in 2019 to -883 g CO2-C m-2 y-1 and -963 g CO2-C m-2 y-1 in 2021 respectively for W and WP sites. It is undeniable that the effect of climate manipulation has induced changes in vegetation composition which produce the changes in temperature and WTD response of GPP and at the same time, the cumulative GPP yearly. The changes in vegetation composition can be observed through the comparison with control plots where the WTD effect remained significant, explaining still in 2021 24.5% of the GPP variance while it is 16% and 13% for W and WP, probably with vegetation less adapted to climate extremes and more WTD-dependent.

This work was supported by the National Science Centre of Poland (NCN) under projects No. 2016/21/B/ST10/02271 and 2020/37/B/ST10/01213.

How to cite: Albert-Saiz, M., Strozecki, M., Rastogi, A., and Juszczak, R.: The increasing effect of temperature on vegetation productivity under climate manipulation and water table depth alteration in a temperate peatland., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14993, https://doi.org/10.5194/egusphere-egu23-14993, 2023.

09:20–09:30
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EGU23-2946
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ECS
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On-site presentation
Renato K. Braghiere, Joshua Fisher, Kara Allen, Edward Brzostek, Mingie Shi, Xiaojuan Yang, Daniel Ricciuto, Rosie Fisher, Qing Zhu, Richard Phillips, Benjamin Sulman, Brian Steidinger, Nadejda Soudzilovskaia, Jing Liang, Kabir Peay, and Thomas Crowther

Most Earth system models (ESMs) do not explicitly represent the carbon (C) costs of plant nutrient acquisition, which leads to uncertainty in predictions of the current and future constraints to the land C sink. While plants acquire nutrients through different uptake pathways, such as from mycorrhizae, direct root uptake, retranslocation from senescing tissues, and biological fixation in the case of nitrogen (N), they usually have different associated C costs. Determining the amount of nutrients acquired through each uptake pathway and the associated C cost could increase understanding of the global C and nutrient cycles, as well as the predictive skills of ESMs.

Here, we integrate a plant productivity-optimizing nutrient (N and phosphorus (P)) acquisition model (Fixation & Uptake of Nutrients, FUN) into the Energy Exascale Earth System (E3SM) Land Model (ELM) to simulate the global C and nutrient cycles (Braghiere et al., 2022). We benchmarked the model with observations (in-situ, remotely sensed, and integrated using artificial intelligence), and other ESMs from CMIP6; we found significant improvements in present C cycle variables estimates. We also examine the impact of mycorrhizal spatial distributions on the global C cycle, since most plant species predominantly associate with a single type of mycorrhizal fungi and uncertainties in mycorrhizal distributions are non-trivial, with current estimates disagreeing in up to 50% over 40% of the land area (Braghiere et al., 2021). Global Net Primary Productivity (NPP) is reduced by 20% with N costs and 50% with NP costs, while modeled and observed nutrient limitation agreement increases when N and P are considered together. Even though NPP has been growing globally in response to increasing CO2, as soil nutrient progressively becomes more limiting, the costs to NPP for nutrient acquisition have increased at a faster rate. This suggests that nutrient acquisition will increasingly demand a higher portion of assimilated C to support the same productivity.

Braghiere, et al. (2022) doi.org/10.1029/2022MS003204

Braghiere, et al. (2021) doi.org/10.1029/2021GL094514

How to cite: Braghiere, R. K., Fisher, J., Allen, K., Brzostek, E., Shi, M., Yang, X., Ricciuto, D., Fisher, R., Zhu, Q., Phillips, R., Sulman, B., Steidinger, B., Soudzilovskaia, N., Liang, J., Peay, K., and Crowther, T.: ­­Carbon Costs of Plant Nutrient Acquisition Improve Present-Day Carbon Cycle Estimates and Limit CO2 Fertilization Effect, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2946, https://doi.org/10.5194/egusphere-egu23-2946, 2023.

09:30–09:40
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EGU23-6649
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ECS
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On-site presentation
Qing Sun, Sebastian Lienert, and Fortunat Joos

Nitrous oxide (N2O) is a greenhouse gas and ozone-depleting agent that is predominately emitted from the land biosphere, linking to the yet only poorly understood carbon-nitrogen cycle. The seasonal cycle of the tropospheric N2O mixing ratio (aN2O), measured at globally distributed air sampling sites, offers an observational model constraint. Recent studies attribute the aN2O seasonality to exchange with N2O-depleted stratospheric air. Yet, how land biosphere N2O fluxes contribute to the seasonal amplitude, phasing, and amplitude growth of aN2O has not been well understood at global scales.

Here we apply surface-atmosphere fluxes from global simulations of the Nitrogen/N2O Model Inter-comparison Project (NMIP) and the Bern3D ocean model to atmospheric transport matrices to simulate aN2O at air sampling sites. Land N2O fluxes from eight NMIP models show broad agreement on seasonal phasing. In contrast, seasonal amplitudes of regionally averaged fluxes differ severalfold across models. For example, seasonal amplitudes range from 2.2 to 5.4 TgN yr­-1 (median: 3.7) for 20oN-40oN and from 1.1 to 4.5 TgN yr­-1 (2.3) for 40oN-60oN during 2001 to 2020. The amplitudes for these two regions increased on average by 155% and 84%, respectively, over the industrial period. The increase predominantly results from anthropogenic activities, e.g, fertilizer application. The seasonal amplitude of regional ocean-atmosphere fluxes (0.2 to 1.1 TgN yr-1) and their changes are comparably small.

The NMIP land fluxes result in seasonal amplitudes of aN2O on average ranging from 0.27 to 0.84 ppb (observed: 0.23 to 0.91 ppb) at six selected stations (Alert and Barrow, Ascension Island, Ragged Point, and Samoa, and Cape Grim). The model spread in aN2O amplitude is up to 0.55 ppb and, thus, large in comparison with observations. The contributions from Bern3D ocean fluxes to aN2O seasonality at the six stations (0.13 to 0.26 ppb) are generally smaller than from land. Substantial data-model mismatches in aN2O seasonal amplitudes and phasing are likely due to neglecting stratospheric fluxes in our models.

Our results demonstrate significant contributions of land biosphere N2O emissions to aN2O seasonality. Model uncertainties in land biosphere fluxes translate into large uncertainties in aN2O seasonality, calling for land biosphere model improvements. In situ aN2O observations, in combination with atmospheric transport and chemistry models, potentially provide a novel top-down constraint for global land biosphere models towards improved projections of C-N coupling, the land carbon sink, and atmospheric CO2 and N2O.

How to cite: Sun, Q., Lienert, S., and Joos, F.: The seasonal cycles of land biosphere N2O fluxes and atmospheric N2O, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6649, https://doi.org/10.5194/egusphere-egu23-6649, 2023.

09:40–09:50
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EGU23-3822
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ECS
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On-site presentation
Cheng Gong, Silvia Caldararu, Jan Engel, Julia Nabel, and Sönke Zaehle

Terrestrial ecosystem acts as important carbon dioxide (CO2) sinks and nitrous oxide (N2O) sources. Ecosystem green-house-gas fluxes could further lead to a climate feedback, which are highly correlated with the C-N coupling. However, magnitudes of such composited feedbacks as well as contributions by individual ecological processes remained certain uncertainties. Here, we applied a terrestrial biosphere model QUINCY with fully C-N-coupling to comprehensively examine responses of CO2 and N2O fluxes to future climate changes and quantify contributions by individual processes. Our results showed that the trade-offs in CO2 and N2O still led a negative feedback (-3386.9 Tg CO2 yr-1) averaged over 2050-2100 under the SSP 5-8.5 scenario relative to SSP 1-2.6 scenario, however, which varies from -1761.7 Tg CO2 yr-1 to -5012.1 CO2 yr-1 with a high or low climate sensitivity to CO2 increases.  Further process analysis showed that the CO2 fertilization effects on ecosystem climate feedbacks were equivalent for high and low climate sensitivity, but the higher climate sensitivity led to less carbon sequestration on tropical plants as well as higher N2O emissions. The climate feedbacks attributed to individual soil processes, including decomposition, nitrification, denitrification and nitrogen biological fixation, were also comprehensively quantified. This finding suggests that reducing the uncertainties in climate sensitivity estimates could be of great significance to better predict future terrestrial ecosystem green-house-gas fluxes as well as corresponding climate feedbacks.

How to cite: Gong, C., Caldararu, S., Engel, J., Nabel, J., and Zaehle, S.: Higher climate sensitivities weaken negative climate feedbacks of terrestrial ecosystem through carbon sequestration and nitrous oxide emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3822, https://doi.org/10.5194/egusphere-egu23-3822, 2023.

09:50–10:00
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EGU23-6448
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ECS
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On-site presentation
Nina Raoult, Philippe Peylin, and Peter Cox

Predicting the responses of terrestrial ecosystems to future global change strongly relies on our ability to accurately model global scale vegetation dynamics and surface CO2 fluxes. However, terrestrial biosphere model carbon cycle processes remain subject to large uncertainties, partly because of unknown or poorly calibrated parameters. 

We can use the unprecedented amount of in situ and Earth Observation data to optimize these model parameters, as well as the considerable advances in parameter estimation techniques. Most of these techniques use Bayesian data assimilation approaches, which allow for objective calibrations of key model processes and parameters against observations, reducing the associated uncertainty. However, calibrating against present-day observations does not necessarily give us confidence in the future projections of the model, given that they are likely to exceed historical and present-day conditions. The relatively shorter timescales of present-day observations mean these cannot be directly used to create constraints on changes in the Earth System over the next century. Instead, we need to develop methods to translate short-term constraints into reductions in long-term projection uncertainty, bridging the gap between contemporary model optimisations and future predictions.

In this presentation, we will discuss two experiments highlighting how we can use parameter estimation to reduce model uncertainty and translate this information into constraints on future climate.

The first demonstrates how we can use manipulation experiments to increase our confidence in optimized parameters. We use data from two nitrogen-limited sites from the Free Air CO2 Enrichment experiment to optimize model parameters. The optimization is performed against ambient and elevated CO2 conditions simultaneously, giving us a better insight into nitrogen limitations on CO2 fertilization at these sites.

The second demonstrates how we can combine local model calibration with the emergent constraint approach. Using a parameter perturbation ensemble, we identify an emergent relationship between the optimal temperature for photosynthesis in tropical forests, and the projected amount of atmospheric CO2 at the end of the century. We combine this with a constraint on the optimum temperature for photosynthesis in tropical forests derived from eddy-covariance measurements and parameter estimation techniques to reduce the likely range of future atmospheric CO2 in a coupled climate-carbon cycle model under a common emissions scenario.

How to cite: Raoult, N., Peylin, P., and Cox, P.: Using parameter estimation to reduce future climate-carbon cycle projection uncertainty, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6448, https://doi.org/10.5194/egusphere-egu23-6448, 2023.

Coffee break
Chairpersons: Benjamin Stocker, Karin Rebel
10:45–10:55
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EGU23-9973
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On-site presentation
Rossella Guerrieri, Alessandra Teglia, Dario Ravaioli, Matteo Bucci, Emma Scisci, Enrico Muzzi, and Federico Magnani

The ability of forests to continue absorbing atmospheric CO2, and hence mitigating climate change, is constrained by global change drivers, such as increasing nitrogen deposition induced by anthropogenic activities. N input from atmospheric deposition can positively affect forest productivity in N-limited temperate and boreal ecosystems. However, under N saturation conditions, a cascade of negative effects can be observed, leading to tree growth decline, increase in soil acidification and N loss pathways, and nutrient imbalance. Experimental simulations of N deposition have been extensively used to directly determine whether atmospheric N input contributes to alleviating N limitation and to understand ecosystem responses. However, the majority of these experiments have considered soil N applications, often applying N doses several order of magnitude higher than ambient deposition, thus not mimicking realistic changes in atmospheric deposition. Moreover, soil applications exclude a priori atmosphere-canopy exchange processes, including direct canopy N uptake. In this context, the experiment established in a mature and eutrophic Fagus sylvatica L. forest in Italy represents a unique resource for advancing understanding on forest responses to global change. At this site, four different treatments have been carried out since 2015: control, canopy (30 kg ha-1 yr-1) and soil (30 and 60 kg ha-1 yr-1) N applications, with doses reflecting more realistic changes in atmospheric deposition (about twice and three times as much as ambient deposition). We asked whether the two experimental approaches (canopy vs. soil applications) can lead to different responses in terms of i) tree growth and intrinsic water-use efficiency (the ratio between photosynthesis and stomatal conductance) and ii) ecosystem nitrogen processes (including plant-microbe interactions). For this purpose, we combined dendroecological analyses (the measure of ring widths and stable carbon isotope composition, δ13C) with the measure of foliar nutrient concentrations and stable nitrogen isotope composition (δ15N) in different forest samples, including foliar, litter, soil main root and ectomycorrhizal root tips. On-going δ13C analyses will provide insight regarding the physiological mechanisms underpinning growth changes in relation to different treatments. Whereas, δ15N in different forest samples will help to elucidate differences in ecosystem N processes between the two approaches, i.e., N retention within the system or increasing N loss pathways and other nutrient limitations due to N saturation. 

How to cite: Guerrieri, R., Teglia, A., Ravaioli, D., Bucci, M., Scisci, E., Muzzi, E., and Magnani, F.: Responses of mature forests to nitrogen deposition: insights from a nitrogen manipulation experiment in Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9973, https://doi.org/10.5194/egusphere-egu23-9973, 2023.

10:55–11:05
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EGU23-10303
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ECS
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On-site presentation
Yunpeng Luo, Petra D`Odorico, Sung-Ching Lee, Xuanlong Ma, Mirco Migglivacca, Matthias Peichl, Benjamin Stocker, and Arthur Gessler

Anthropogenic nitrogen (N) deposition and fertilization in the past decades shifted the ecosystem stoichiometry with potentially profound impacts on vegetation activity and ecosystem functioning. Current N-addition experiments mostly focus on leaf-level or individual plants at the plot scale, whereas studies investigating the responses of vegetation dynamics to N-addition at the landscape level are lacking. It is especially unclear how ecosystems with different water availability (water-limited versus water-surplus) respond to elevated N input. We compared vegetation dynamics and ecosystem functioning in two unique ecosystem-scale N addition experiments – one Mediterranean tree-grass ecosystem and one boreal evergreen forest. At each site, one pair of landscape-scale N addition was set up by adding N onto the footprint area of one eddy covariance (EC) tower, with another EC tower without N addition used as a control. We hypothesize that their different water availability can exert different responses in vegetation phenology and gross primary productivity (GPP).  Since the start of the experiments, we found that the fertilized treatments in both experimental sites have had higher amplitudes of GPP and more rapid green-up and leaf senescence compared to the control. However, phenological transition dates (PTDs) defining the start and end of the growing seasons (SOS, EOS), derived from GPP at the two sites show different patterns. During the green-up period, SOS was similar between the fertilized and control treatments at the Mediterranean site since the vegetation green-up here was mainly controlled by the timing of precipitation. In the boreal forest, however, the fertilized treatment was greening slightly later than the control. In the leaf senescence period, the fertilized treatment senesced earlier in the Mediterranean ecosystem compared to the control. In contrast, the fertilized treatment delayed in EOS compared to the control in boreal forests.  We propose that increased leaf area index and canopy greenness in the fertilized (based on the observed increasing evapotranspiration) compared to the control treatment in both ecosystems, along with different vegetation composition, probably contributes to the divergent response of EOS at the two sites with different water availability. This study underscores the necessity to take different water availability into account when evaluating the effects of N addition on vegetation dynamics. 

How to cite: Luo, Y., D`Odorico, P., Lee, S.-C., Ma, X., Migglivacca, M., Peichl, M., Stocker, B., and Gessler, A.: Divergent phenology response to nitrogen addition between a Mediterranean and a boreal forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10303, https://doi.org/10.5194/egusphere-egu23-10303, 2023.

11:05–11:15
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EGU23-2202
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On-site presentation
Tea Thum, Outi Seppälä, Holly Croft, Silvia Caldararu, Amanda Ojasalo, Cheryl Rogers, Ralf Staebler, and Sönke Zaehle

Understanding the interactions between atmosphere and vegetation in changing climatic conditions is important so that we can predict the carbon sequestration potential of ecosystems. Helpful tools here are the terrestrial biosphere models (TBMs), since they include detailed ecophysiological process descriptions, e.g. the manifold interactions between the carbon and nitrogen cycles. However, the modelling of the nitrogen cycle poses challenges and having observational constraints on nitrogen cycle is crucial. Current remote sensing products offer estimates of leaf chlorophyll (Cab), that is related to the nitrogen cycle. In this study we want to assess how useful Cab observations are at site scale to constrain a TBM.

 

In this work we are studying a temperate mixed forest, Borden, located in Canada. We use a TBM QUantifying Interactions between terrestrial Nutrient Cycles, QUINCY, to model this site. From the site we have long-term (20 years) flux tower and LAI (from PAR measurements) observations together with leaf level observations of leaf chlorophyll (Cab), leaf nitrogen, and photochemical parameters of maximum carboxylation rate (Vcmax) and maximum potential electron transport rate (Jmax). 

 

The QUINCY model was predicting too late leaf senescence, which we tuned using the site level data. The amount of leaf nitrogen was originally quite successfully simulated by QUINCY, but the amount of simulated Cab was too low. Matching the simulated Cab values with the observations did not have a pronounced effect on the GPP. Additionally, the development of LAI and Cab were originally fully coupled in QUINCY, whereas the observations showed a delayed development of Cab compared to LAI. When we implemented this decoupling between LAI and Cab, an improvement of simulated GPP compared to the observations was found. Also then the simulated Vcmax and Jmax showed better correspondence to the observations. 

 

Assessment of the long-term behaviour of the model at the site showed that the model was able to capture the drought-induced drawdown of carbon fluxes taking place in 2007. The observations showed an increase in the component fluxes of carbon during the time period, but this was not replicated by the model. The start of season (SOS) and end of season (EOS) were estimated from both the simulated and observed GPP and LAI using a simple threshold method. The model was more successful in capturing the changes in the growing season metrics estimated by LAI than by GPP. The model was predicting too late onset of GPP in many years, but captured largely the interannual variation of SOS in observed GPP. 

 

This study paves the way for work using remotely sensed leaf chlorophyll in evaluation and improvement of the QUINCY model.

How to cite: Thum, T., Seppälä, O., Croft, H., Caldararu, S., Ojasalo, A., Rogers, C., Staebler, R., and Zaehle, S.: Using leaf chlorophyll observations to improve carbon cycle modelling at a temperate mixed forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2202, https://doi.org/10.5194/egusphere-egu23-2202, 2023.

11:15–11:25
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EGU23-14426
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ECS
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Highlight
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On-site presentation
Clara Steller, Vincent Humphrey, Erich Fischer, and Reto Knutti

Because long-term observations are sparse and heavily affected by inter-annual variability, the detection of forced trends in land carbon uptake has been remarkably difficult. While changes in aggregated monthly or yearly carbon uptake have been heavily studied, changes in the diurnal cycle of carbon uptake remain uninvestigated. Here, we evaluate long-term changes in three-hourly Net Ecosystem Production (NEP) and the contribution of different times of the day to long-term changes in the terrestrial carbon sink. We first show that between 1950 and 2014, five CMIP6 models show a significant increasing trend in the diurnal NEP amplitude (DNA). Second, we show that DNA trends have a much higher signal-to-noise ratio compared to trends in NEP itself, and linearly scale with long-term annual NEP. Evaluating these model-based results against observations, we show that positive DNA trends are also found at a majority of observational eddy-covariance sites between 1990 and 2022. The positive correlation between DNA and long-term NEP is also confirmed by these observations. Our results reveal a widespread but previously undocumented emergent climate signal in terrestrial carbon exchange at the diurnal scale with the potential to serve as a new observational constraint for Earth system models.

How to cite: Steller, C., Humphrey, V., Fischer, E., and Knutti, R.: The Rising Pulse of Land Carbon Uptake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14426, https://doi.org/10.5194/egusphere-egu23-14426, 2023.

11:25–11:35
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EGU23-10124
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On-site presentation
Damiano Zanotelli, Dolores Asensio, Michaela Schwarz, Fadwa Benyahia, Albin Hammerle, Ahmed Ben Abdelkader, Flavio Bastos Campos, Torben Callesen, Carlo Andreotti, Leonardo Montagnani, Massimo Tagliavini, and Georg Wohlfahrt

Heat waves are predicted to increase in frequency and intensity, endangering the productivity of agroecosystems including grapevines. In this work, we analyzed the effects of the long and intense heat wave (HW) occurring in July 2022 on the eco-physiological performance of a vineyard located in northern Italy (Caldaro, Province of Bolzano). The vineyard hosts two white grape cultivars (Sauvignon Blanc and Chardonnay on SO4 rootstock) with an average planting density of 6,500 vines ha-1 and is equipped with a drip irrigation system. The interrow alleys are covered by grasses or cover crops. Summer 2022 showed a continuous daily temperature increase from the second week of July and peaked in a heat wave lasting 8 days (DOYs 196-203) with maximal Tmax= 38 and average Tmax= 36°C. The HW period was then interrupted by summer storms and rain. 

The methodology included continuous monitoring of NEE (-NEP), Reco, GPP, ET and energy fluxes by eddy covariance method. Continuous measurements at the plant scale included sun-induced chlorophyll fluorescence, active chlorophyll fluorescence, and sap-flow rates. Periodically, leaf gas exchange, leaf water potential and chlorophyll content were also recorded. The period considered for the analysis stretched from July 1 to August 11.

There was a general mild decreasing trend of GPP when the air temperature increased in July, reaching the minimum values during the HW (< 10 g C m-2d-1). Leaf photosynthesis also slightly decreased during the HW in both varieties down to values of 6-7 µmol CO2 m-2s-1. Interestingly, even during the HW, GPP always markedly increased the day after irrigation water was supplied (5 irrigation events were performed in July with a total of approximately 45 L/vine).

Reco decreased when the air temperature increased, but a few days before the end of the HW it increased again, a process that was even more pronounced following the rainy period after the HW when negative values of NEP were recorded.

Vineyard ET and vine transpiration did not show a clear response to the HW, while they both increased each time vines were irrigated, suggesting that most ET in that period derived from vine transpiration and not from the vineyard alleys. Interestingly, after the end of the HW, vineyard ET did not increase despite the increased soil moisture occurring also in the alleys. The energy partitioning was unaffected by the HW, with the Bowen ratio dropping below 0.4 after the irrigations. Continuous monitoring of active chlorophyll fluorescence showed a slight increase in NPQ parameter (measured only on Chardonnay leaves) in the last and hotter days of the HW, while Fv/Fm was not affected by the higher temperatures.

In conclusion, despite the exceptional (for the cultivation area) intensity of the 2022  HW, the vines showed good tolerance to heat stress. We speculate that irrigation played an important role in the vines’ performance. The NEP, however, decreased during the HW and especially after its end due to soil-moisture triggered increasing Reco, which shifted the vineyard from sink to source of atmospheric CO2.

How to cite: Zanotelli, D., Asensio, D., Schwarz, M., Benyahia, F., Hammerle, A., Ben Abdelkader, A., Bastos Campos, F., Callesen, T., Andreotti, C., Montagnani, L., Tagliavini, M., and Wohlfahrt, G.: Vineyard water and carbon dioxide exchange during a heat wave, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10124, https://doi.org/10.5194/egusphere-egu23-10124, 2023.

11:35–11:45
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EGU23-6684
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On-site presentation
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Xiao Ying Gong, Wei Ting Ma, Yong Zhi Yu, and Xuming Wang

Water-use efficiency (WUE) is a key determinant of carbon and water fluxes at scales ranging from individual plants to continents and thus a key driver of hydro-climatic changes and carbon models. Multiple lines of evidence suggest that WUE of plants increases with atmospheric CO2, pointing to potential changes in physiological forcing of global carbon and hydrological cycles. Although the increase in forest WUE with atmospheric CO2 is widespread, declines in tree growth have been observed in different forests. These controversial results highlight the need to re-evaluate the historical trend of forest WUE.

13C signatures (i.e., δ13C) of plant organic matter is a useful tool for estimating WUE at temporal scales ranging from days to centuries. This estimation relies on photosynthetic 13C discrimination models that have different assumptions about the components of isotope discrimination. Mesophyll conductance is a key uncertainty in estimated WUE owing to its influence on diffusion of CO2 to sites of carboxylation.

We developed a 13C-based WUE model that takes into account the effect of mesophyll conductance and tested its performance with experimental data. We applied this model to 464 δ13C chronologies in tree-rings of 143 species spanning global biomes. Adjusted for mesophyll conductance, mean sensitivity of WUE to atmospheric CO2 (0.15 ppm ppm-1) was considerably smaller than those estimated from conventional modelling (0.23-0.30 ppm ppm-1). Our results showed a 10-ppm gain in WUE during the 20th century. Ratios of internal-to-atmospheric CO2 (ci/ca) in leaves maintained constant over time but differed among biomes and plant taxa. Our results also suggest that ratios of chloroplastic-to-atmospheric CO2 (cc/ca) are constrained over time, but this result is associated with the sensitivity of gs /gm ratio to CO2 which need further evaluation.

Over the last century, a general increase in forest WUE across the globe has been confirmed. However, our study shows that forest WUE may have not increased as much as previously suggested and that projections of CO2 fertilization may need to be adjusted accordingly.

How to cite: Gong, X. Y., Ma, W. T., Yu, Y. Z., and Wang, X.: Overestimated water-use efficiency responses to rising CO2 revealed by tree-ring 13C record, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6684, https://doi.org/10.5194/egusphere-egu23-6684, 2023.

11:45–11:55
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EGU23-8575
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On-site presentation
Tchodjowiè Israel Kpemoua, Pierre Barré, Sabine Houot, and Claire Chenu

The influence of dry-wet cycles (DWC) on soil organic carbon (SOC) decomposition is still debated given the somehow controversial results observed in the literature. The objective of this study was to evaluate the effects of DWC on SOC mineralization relative to various moisture controls in 7 treatments from two long-term French field experiments presenting contrasted SOC concentrations. We conducted a laboratory incubation to quantify CO2 emissions upon four soil moisture scenarios: continuously wet (WET), continuously moderately wet (MWET), continuously dry (DRY) and dry-wet cycles (DWC). We also calculated the SOC mineralization that would correspond to the average water content in DWC (mean_DWC). Our results showed that across all treatments the daily carbon mineralization rate increased with soil moisture (WET>MWET>DRY). In DWC scenario, mineralization rates fluctuated with the changes in soil moisture. As soils dried, daily mineralization rates decreased and the subsequent soil rewetting, to pF 1.5, caused a rapid mineralization flush or "Birch effect". However, these flushes did not compensate for the low mineralization rates in the drying phase as the cumulative mineralization was not higher in the DWC scenario compared to the mean_DWC which was the scenario with equivalent water content as the DWC. We also observed that not accounting the CO2 emissions in the drying phase could lead to an overestimation of the effect of DWC. We recommend to measure continuously the soil respiration during dry-wet experiments and to compare the CO2 emitted in DWC with a control that has a water content equivalent to the average water content in DWC. In addition, we questioned the importance of the effect of dry-wet cycles on overall soil respiration.

How to cite: Kpemoua, T. I., Barré, P., Houot, S., and Chenu, C.: Accurate evaluation of the Birch effect requires continuous CO2 measurements and relevant controls, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8575, https://doi.org/10.5194/egusphere-egu23-8575, 2023.

11:55–12:05
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EGU23-1576
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Virtual presentation
Gangsheng Wang

Soil carbon (C) and nitrogen (N) cycles and their complex responses to environmental changes have received increasing attention. However, large uncertainties in model predictions remain, partially due to the lack of explicit representation and parameterization of microbial processes. One great challenge is to effectively integrate rich microbial functional traits into ecosystem modeling for better predictions. Here, using soil enzymes as indicators of soil function, we developed a competitive dynamic enzyme allocation scheme and detailed enzyme-mediated soil inorganic N processes in the Microbial-ENzyme Decomposition (MEND) model. We conducted a rigorous calibration and validation of MEND with diverse soil C-N fluxes, microbial C:N ratios, and functional gene abundances from a 12-year CO2×N grassland experiment (BioCON) in Minnesota, USA. In addition to accurately simulating soil CO2 fluxes and multiple N variables, the model correctly predicted microbial C:N ratios and their negative response to enriched N supply. Model validation further showed that, compared to the changes in simulated enzyme concentrations and decomposition rates, the changes in simulated activities of eight C-N associated enzymes were better explained by the measured gene abundances in responses to elevated atmospheric CO2 concentration. Our results demonstrated that using enzymes as indicators of soil function and validating model predictions with functional gene abundances in ecosystem modeling can provide a basis for testing hypotheses about microbially-mediated biogeochemical processes in response to environmental changes. Further development and applications of the modeling framework presented here will enable microbial ecologists to address ecosystem-level questions beyond empirical observations, toward more predictive understanding, an ultimate goal of microbial ecology.

How to cite: Wang, G.: Soil enzymes as indicators of soil function: a step toward greater realism in microbial ecological modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1576, https://doi.org/10.5194/egusphere-egu23-1576, 2023.

12:05–12:15
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EGU23-10109
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ECS
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On-site presentation
Chun Chung Yeung, Olalla Diaz Yanez, and Harald Bugmann

Current models of soil biogeochemistry are facing difficulties to match the observed amount and composition of soil organic carbon (SOC). An important omission is that nitrogen (N) can directly and interactively affect microbial decomposition processes, rather than merely being a nutrient for plant production and a passive subordinate of C flow based on stoichiometric coupling. In the past decades, many litter manipulation studies have shown that SOC stocks do not increase significantly in response to experimental increases of litter C input. Moreover, many N fertilization studies showed that SOC accrual is predominantly driven by changes in heterotrophic respiration instead of litter production; i.e., soluble N directly affects multiple processes such as the activities of various C-cycling enzymes, microbial growth (e.g., via carbon use efficiency, CUE), and necromass production.

In order to reconcile empirical insights with simulated patterns of SOC and N dynamics, we developed variants of the Century soil submodel coupled with the stand-scale forest gap model ForClim. We implemented equations to capture neglected processes, including 1) the effect of available N on lignin decomposition; 2) the effect of available N on low C:N substrates (e.g., protein) degradation; 3) the effect of available N on microbial CUE dynamics. We tested the full combination of model variants comprising new or alternative equations against multi-level observational patterns, over large gradients of climate and fertility in Swiss forests.

The models reconcile that factors affecting C output (decomposition) predominantly control the site-to-site variation of equilibrium SOC stocks, instead of factors affecting litter C input. We further identified the individual processes essential for shaping the geographical pattern (across different climates, forests, and soil types) of the amount and composition of SOC. We conclude that taking into account the direct effects of available N on microbial processes is essential to improve the realism and accuracy of soil models under global change (i.e., reconciling the mainstream theory of plant-derived vs. microbial-derived SOC accumulation pathways), thus avoiding the need of frequent parameter tuning inherent in “C-centric” models.

How to cite: Yeung, C. C., Diaz Yanez, O., and Bugmann, H.: Nitrogen availability as a master control of plant-derived vs. microbial-derived soil carbon accumulation – insights from a novel model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10109, https://doi.org/10.5194/egusphere-egu23-10109, 2023.

12:15–12:25
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EGU23-5716
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ECS
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On-site presentation
Gregory Jones, Athanasios Paschalis, and Bonnie Waring

Currently, few scalable, cost-effective CO2 removal (CDR) strategies exist to mitigate anthropogenic climate change. Enhanced rock weathering (ERW) is a strategy in which finely ground silicate rock reacts with atmospheric CO2 and produces weathering products that are transported to the ocean for long-term storage. Despite detailed knowledge of chemical weathering and its role in the carbon cycles at geologic timescales, few data display the efficacy of ERW for CDR at timescales appropriate for climate mitigation. To address this, we use the first large-scale field trial of ERW combined with tree planting at an afforestation experiment in mid-Wales. A factorial experimental design will enable us to determine the influence of basalt application and tree functional type on rock weathering and nutrient cycling parameters, such as soil pore water pH, alkalinity, cation concentrations and soil carbon. Here, we focus on the description and installation of the experiment, its monitoring protocol, and data analysis from the first two years of the site observations. We also outline how the data can be introduced into a mechanistic eco-hydrological model. Ultimately, we aim to synthesize these findings to inform predictions of global regions where ERW could be most effective for CDR.

How to cite: Jones, G., Paschalis, A., and Waring, B.: Harnessing enhanced rock weathering in a forestry context, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5716, https://doi.org/10.5194/egusphere-egu23-5716, 2023.

Posters on site: Fri, 28 Apr, 14:00–15:45 | Hall A

Chairpersons: Benjamin Stocker, Sönke Zaehle, Teresa Gimeno
A.241
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EGU23-203
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ECS
Dilip Naidu, Ashwin Seshadri, and Sumanta Bagchi

Climate plays a vital role in the carbon (C) uptake through vegetation productivity (Gross Primary Production; GPP) that is crucial to the persistence of the land as a carbon sink, thereby resulting in negative land-climate feedbacks. Large uncertainties persist in understanding the role of climate variability on this C flux, which influence future projections using Earth System Models (ESMs). One important source of uncertainty arises from the temporal variability in the carbon influx, and this includes effects of autocorrelation—i.e., similarity in observations with time-lag due to temporal structuring (“memory”) in the underlying dynamics. Evidence of the presence of memory in C uptake through GPP arises from field-based measurements through eddy covariance flux towers, but these lack widespread spatial distribution across environmental conditions and ecosystems. Therefore, estimating memory in the C cycle and its drivers on the global scale is important to our understanding of the global C cycle. For this, we used remotely sensed long-term GPP data from MODIS over the past two decades (2001-2021), to estimate long-term memory in C cycling through C-uptake by vegetation. Additionally, we also examined how the climate variables – temperature and precipitation- that are known to drive C influx, influenced the memory in C-uptake. We find that memory occurs in satellite-based estimates of GPP, corroborating field-based measurements. Interestingly, the memory in the C cycle was not limited to either short- or long-term but consisted of both these characteristics across different timescales. Climate variability through temperature and precipitation influenced memory and their effects are heterogeneous across ecosystems. With climate variability predicted to increase in the near future, our results suggest that these effects are likely to be consequential for the memory in C-uptake and, ultimately on the dynamics of the global C cycle. Therefore, estimating the memory in C cycle and its variation, is crucial for understanding as well as predicting the C-influx, under present and future climate change scenarios. 

How to cite: Naidu, D., Seshadri, A., and Bagchi, S.: Climate-driven changes to the long-range fluctuations in vegetation production: Consequences for the global carbon cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-203, https://doi.org/10.5194/egusphere-egu23-203, 2023.

A.242
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EGU23-2939
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ECS
Sayuri Sagisaka and Carl P. Mitchell

The methylation of mercury by anaerobic microbes in wet soils and sediment significantly increases its bioaccumulation potential into wildlife. Methylation is also counter-acted by demethylation processes, with the balance between methylation and demethylation processes ultimately controlling the amount of methylmercury in a system. Given that microbial activities are intricately linked with temperature, climatic changes should impact mercury methylation and demethylation processes, but this is not well-characterized in mercury research. In this presentation, I will discuss the outcome of better understanding mercury methylation and demethylation processes and rates in boreal wetland soils, as affected by temperature. To examine this, we have included a series of controlled, closed-system, flow-through experiments using boreal wetland soils from both forest-impacted and unimpacted wetlands in dark growth chambers across a range of realistic temperatures (5, 10, 15, 20, 25 °C). Mercury methylation and demethylation processes were examined in soil cores using enriched mercury isotope incubations and analyzed against measures of microbial activity and soil/water chemistry. Results from this study are expected to allow us to begin modeling mercury cycling processes with respect to climate and other environmental changes.

How to cite: Sagisaka, S. and Mitchell, C. P.: Mercury methylation and demethylation on impacted wetland soils: effects of temperature, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2939, https://doi.org/10.5194/egusphere-egu23-2939, 2023.

A.243
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EGU23-2953
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ECS
Linxin Liu, Ke Zhang, and Giovanni Forzieri

Understanding how terrestrial ecosystem water use efficiency (WUE) responds to climate change is critical to accurately representing the carbon-water cycle processes. However, the dynamics of WUE under seasonal climate variations and biome-specific characteristics remain still unclear. In this study, we integrated two satellite-based retrieval algorithms to estimate gross primary productivity (GPP) and evapotranspiration (ET). Such indexes served as input to quantify ecosystem WUE (GPP/ET) and explore its dynamics during the dry and wet seasons from 2001 to 2018 in China’s key tropical to subtropical transitional zones, i.e., Yunnan Province. Results show large spatial heterogeneity and seasonal difference in WUE over the observational period. During the dry season, the increasing trends in GPP and ET have led to contrasting WUE patterns in forest and non-forest biomes, leading to positive and negative WUE trends, respectively. During the wet season, the declining trends in GPP occurring in combination with opposite trends in ET, have caused decreasing WUE consistently across all biomes except croplands, likely further modulated by human factors. The observed changes in WUE appear primarily driven by variations in air temperature (Ta) and vapor pressure deficit (VPD) during both dry and wet seasons. Overall, these results provide a valuable case for a better understanding of the carbon-water interplay in tropical-subtropical transitional zones and provide new insights to improve our capacity to predict the terrestrial ecosystem’s response to climate change.

How to cite: Liu, L., Zhang, K., and Forzieri, G.: Recent variations in ecosystem water use efficiency to seasonal climate variability in China's key tropical-subtropical transitional zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2953, https://doi.org/10.5194/egusphere-egu23-2953, 2023.

A.244
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EGU23-3972
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Silvia Medina Villar, Ana de Torre Sáez, Antonio Manuel Montoya Ruíz, Paloma de las Heras Puñal, and M. Esther Pérez Corona

Biological invasions may affect diversity in different ways. In the case of exotic invasive plants, as soon as they arrive to a new ecosystem they may directly compete for resources with native plants, make the native environment toxic for native plants or modify soil properties in a way that hinder native plants. The exotic invasive trees, Ailanthus altissima and Robinia pseudoacaica, are listed as 20 of the most harmful exotic invasive species in Spain, but their mechanisms of impact are still not clear. In this study we investigated the extent to which these exotic invasive trees may affect understory native plants via soil modifications. In a riparian forest, we collected soils around exotic (A. altissima and R. pseudoacaica) and native trees (Populus alba) trees. Half of the soils were supplemented with activated carbon (AC) to reveal possible effects via the release of phytotoxic compounds from the invasive trees to the soil. We added seeds of native herb species (target species), Trifolium repens and Dactylis glomerata, to pots containing the different soils. We moistened the soils to favor seed germination. The emergence of plants was counted daily, and the aerial biomass reached by the plants was also measured. Independently of the addition of AC, compared to native soils, those of the exotic invasive trees negatively affected the target species. The biomass of T. repens and the emergence speed of D. glomerata was lower in A. altissima soils than in native soils. The emergence speed of T. repens was affected by both exotic soils. The effects produced by the exotic trees may be attributed to changes in soil properties but not to the release of phytotoxic compounds.

How to cite: Medina Villar, S., de Torre Sáez, A., Montoya Ruíz, A. M., de las Heras Puñal, P., and Pérez Corona, M. E.: Exotic invasive trees affect germination and growth of understory plants via soil modifications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3972, https://doi.org/10.5194/egusphere-egu23-3972, 2023.

A.245
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EGU23-5871
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ECS
Laura Dobor, Peter Petrík, Ina Zavadilová, Ladislav Šigut, Dóra Hidy, Nándor Fodor, Zoltán Barcza, Tomas Hlásny, and Katarína Merganičová

Approximately 30% of anthropogenic carbon dioxide emissions are removed from the atmosphere annually by land-based carbon sinks, mainly forests. Extreme weather events such as droughts and heatwaves are expected to be more frequent and severe in the future affecting the carbon-water balance of ecosystems. Although empirical studies elucidate many of these processes, some questions cannot be addressed directly and require constructing in silico representations of real ecosystems. Process-based ecosystem models have recently received increased recognition due to their structural improvements and the increasing success of reproducing complex feedback mechanisms of carbon and water cycles.

We used the Biome-BGCMuSo biogeochemical model to simulate pools and fluxes of carbon, water, and nitrogen in vegetation, litter, and soil on a daily scale. The model is under continuous development and in the last few years, the hydrological cycle submodel went through substantial improvements. We examined the model performance regarding water and carbon cycle simulation using the data from an ecosystem station covered by a circa 100-year-old unmanaged beech forest. The site is included in the FLUXNET global network of micrometeorological tower sites and is operated by the Global Change Research Institute of the Czech Academy of Sciences. The extensively tested model can help to understand complex feedback mechanisms under drought events as well as future climatic conditions and estimate future carbon sink potentials in Central Europe. 

In particular, we (i) evaluated the model performance using biomass, leaf area index (LAI) measurements, five-year-long eddy-covariance measurements of net ecosystem exchange (NEE) and evapotranspiration (ET), (ii) developed an efficient benchmark framework that highlighted structural and/or functional errors in the model, (iii) analyzed the simulated carbon and water cycle under drought events (consecutive dry days) occurring different time of the year and (iv) projected the effects of climate change on the forest carbon and water cycle up to 2100 using climate change scenarios from the FORESEE climatological dataset.

We found that the simulated biomass and LAI values are in the range of the observations, NEE and ET are overestimated by 5% and 11% during the vegetation period, respectively. Simulation runs assuming 30-days drought events at different months in five different years caused immediate NEE decrease compared to simulations without drought events. We found the largest NEE difference (up to 10% on the average of five years) in the cases when the drought occurred in July, August, or in September. Simulations driven by climate change scenarios showed that NEE is expected to increase by the of the century, while the ET does not show any significant change in the future. 

How to cite: Dobor, L., Petrík, P., Zavadilová, I., Šigut, L., Hidy, D., Fodor, N., Barcza, Z., Hlásny, T., and Merganičová, K.: Advances and limitations in carbon and water cycle modeling using the Biome-BGCMuSo biogeochemical model in a Central European beech forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5871, https://doi.org/10.5194/egusphere-egu23-5871, 2023.

A.246
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EGU23-7213
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ECS
Emil Andersen, Josefine Walz, Niki LeBlans, Anders Michelsen, Johan Olofsson, and Ellen Dorrepaal

In the Arctic, much of the year is cold and dark and often snow cover is present. Due to these limitations for active photosynthetic growth during such extended period, plants are challenged. However, while their aboveground parts have a clear seasonal bound by available light, the same may not be the case belowground. Here, temperature, moisture, and nutrient availability may be more important for their activity, which may benefit from a thick snow cover. Recent studies have shown that even after senescence aboveground, plant roots continue to grow in arctic ecosystems, but it is not known for how long into the winter they can remain active in nutrient uptake.

To better understand the year-round variation in potential plant N-uptake during a full year in the Arctic, we set up an experiment with non-fertilising 15N-addition (applied as NH4NO3) each month, followed by destructive harvests the month after. 15N-recovery was then measured in aboveground and (attached) belowground parts (separated into plant functional groups), in (unattached) coarse and fine roots, and in microbial biomass as well as in extractable inorganic N. This was done for two sites in northern Sweden differing in precipitation regime and thus snow cover thickness and duration.

Overall, our results show that there is clear potential for plants to take up N all year round, with winter potential for N-uptake matching or exceeding summer levels for evergreen and deciduous shrub as well as graminoid species. Shrubs have slightly reduced uptake of 15N during the autumn (beginning of snowfall) and spring (snowmelt). Difference in 15N-uptake between the sites differing in snow depth was smaller than expected, possibly because snow fall was high for both sites during the measurement year causing the snow depth to reach a critical threshold for decoupling soil from air temperature fluctuations.

Our results suggest that if N is available in the soil and mobile enough to reach the roots, arctic plants will be able to acquire these resources irrespective of the season. It is therefore important to also consider the period outside of the “active growing” season for understanding plant activity and N-relations. Furthermore, the arctic winters are more sensitive to climate change and increasing temperatures will especially impact this season. Without understanding belowground activity in winter, it is therefore hard to predict future outcome of a changing planet.

How to cite: Andersen, E., Walz, J., LeBlans, N., Michelsen, A., Olofsson, J., and Dorrepaal, E.: Plant roots are also hungry for nitrogen in winter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7213, https://doi.org/10.5194/egusphere-egu23-7213, 2023.

A.247
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EGU23-8333
Bruno Delvaux and Zimin Li

Acid soils cover approximately 40% of the world's land area and 50% of potential arable land. Net acidification is a natural process occurring wherever annual precipitation exceeds evapotranspiration. It can be accelerated or blocked by the use of fertilizers and amendments. Phytoliths are fine-sized biogenic silica particles that can either dissolve to contribute to the global cycle of silicon (Si) or persist in soils and sediments over millennia

Here, we study the resilience of phytoliths in a loess derived Luvisol maintained as a bare fallow for nearly one century (1929-2019). We compared a control with plots affected by the prolonged use of ammonium sulfate [(NH4)2SO4] or calcium carbonate [CaCO3]. A diachronic dynamic of the kinetic release of dissolved Si (DSi), aluminum (Al) and germanium (Ge) was carried out using a dilute saline solution. Molar Al/Si and Ge/Si ratios were used to identify the DSi source and pH was measured at each kinetic step. Phytolith content was assessed by heavy liquid separation. Extracted phytoliths were separated as not-, little- and highly-weathered by counting dissolution cavities per 100 µm2.

Over the period 1929-2019, pH decreases from 6.0 to 5.7 with no input, from 6.0 to 3.5 under prolonged use of (NH4)2SO4, but increased from 6.0 to 8.5 under systematic liming with CaCO3. Using the total reserve in bases (TRB) as a proxy for the soil Acid Neutralizing Capacity (ANC), we observed that TRB was 110 cmol(+)kg-1 in 1929. TRB (cmol(+)kg-1) decreased to 94 and 84 with no input and (NH4)2SO4, respectively, while it increased to 160 with CaCO3 indicating, respectively: net acidification, accelerated net acidification and net alkalinization.

Clay minerals and phytoliths were the privileged source of DSi under prolonged use of (NH4)2SO4 and CaCO3, respectively. Phytolith content was around 14 g kg-1 in 1929. It slightly decreased over a century with no input and CaCO3 supply, but not under prolonged use of (NH4)2SO4. In addition, the proportions of not-little-highly weathered phytoliths were 26-36-38 % with no input, 21-37-42% with CaCO3 and 42-33-25% with (NH4)2SO4 indicating a better resilience of phytoliths under accelerated acidification.

How to cite: Delvaux, B. and Li, Z.: Net acidification preserves phytoliths over a century in a bare fallow soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8333, https://doi.org/10.5194/egusphere-egu23-8333, 2023.

A.248
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EGU23-9160
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ECS
Zimin Li and Bruno Delvaux

Phytoliths are considered by biogeochemists and soil scientists as an important reservoir of mobile Si in the soil-plant system due to their relatively high dissolution rate. However, they are used in other disciplines as microfossils to reconstruct paleoenvironments because of their stability over millennia. Thus, on one side, phytoliths contribute massively to the continental export of dissolved silica to rivers and oceans, hence to the global silicon (Si) cycle, and, on the other side, they persist in soils and sediments. In addition to phytolith properties, soil processes can enhance their resilience, e.g., surface passivation through aluminum (Al) loading or redox-dependent iron (Fe) coating, pH buffering and aggregation.

Here, we highlight the impact of aggregation on the release of dissolved Si (DSi) from aggregates built up from assemblages including organic matter, phytolith, quartz, clay mineral and Fe oxide. The source of DSi was assessed using Al/Si and Ge/Si ratios in aqueous extracts obtained kinetically.

Aggregation significantly reduced the release of DSi particularly when variable charge components were amorphous. In this case, the source of DSi was unequivocally allophane, the dissolution of which was enhanced by pH below 5 (3.7-4.9). In contrast, in aggregates involving crystalline variable charge, DSi was released from phytoliths. In this case, Fe oxide had a significant effect on DSi release through both the aggregation process and pH control above 5 (5-8). Phytolith preservation in aggregates was effective at low oxide content (20 g kg-1). Yet, the increase in pH enhanced phytolith dissolution.

Soil and sediments may thus contain two pools of phytoliths: fresh and stabilized phytoliths. The first reservoir is an important source of aqueous Si, and contributes actively to the Si soil-to-plant cycle and the DSi transfer to the hydrosystem. Yet, Si can be retrieved from the global Si cycle through phytolith entrapment in aggregates. This process contributes to the second pool of stabilized phytoliths. However, pH buffering significantly affects the impact of aggregation and the source of DSi. Indeed, acidic conditions enhance the dissolution of clay minerals while they decrease the dissolution rate of phytoliths

How to cite: Li, Z. and Delvaux, B.: Impacts of soil aggregation on the mobility of silicon in model variable charge soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9160, https://doi.org/10.5194/egusphere-egu23-9160, 2023.

A.249
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EGU23-10120
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ECS
Jordi Buckley Paules, Athanasios Paschalis, Simone Fatichi, and Bonnie Warring

Climate change is increasingly affecting crop production, boosting crop yields in some parts of the world whilst decreasing them in others. The UK is a prime, albeit condensed example of this variability. This is due to the UK’s noticeable regional heterogeneity when it comes to present and projected future climate. Subsequently, the impact of climate change on UK crop yields is likely to be spatially non-uniform as well as crop-specific. Thus, any blanket approach to agricultural adaptation in light of climate change is likely to be sub-optimal. In light of this, we here propose a quantitative assessment to support regional agricultural policy. We examine how crop-specific yields (e.g., Maize, Wheat, Potatoes…) are likely to vary spatially in the UK towards the end of the 21st century under a worst case RCP 8.5 climate change scenario. To achieve this we use the latest generation convection permitting model projections offered by the Met Office (UKCP18) which allow for climate projections at ecohydrological relevant spatiotemporal scales. These climate projections are then used to drive T&C-Crop, a recently developed process-based ecosystem model with a novel agricultural module.

How to cite: Buckley Paules, J., Paschalis, A., Fatichi, S., and Warring, B.: UK crop yields towards the end of the 21st century under a worst case RCP 8.5 climate change scenario: Using the UKCP18 convection permitting model to drive T&C-Crop, a recently developed process-based ecosystem model with a novel agricultural module., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10120, https://doi.org/10.5194/egusphere-egu23-10120, 2023.

A.250
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EGU23-13968
Tejasvi Chauhan and Subimal Ghosh

Mangroves are vital for resilience of coastal communities against climate extremes. They have high carbon densities and sequestration rates which makes them a promising tool for carbon removal from atmosphere using terrestrial vegetation. However, human activities like deforestation and rapid urbanisation pose a major threat to mangroves globally. Sundarbans in South Asia are the largest continuous mangrove forest in the world and due to rampant degradation by human activities, they have been classified as ‘endangered’ under the Red List of Ecosystems. In addition to physical damage to mangroves caused by climate extremes, human activities change the chemical composition of soil leading to changing nutrient availability for mangroves. The ratio of carbon to nitrogen to phosphorous (also called the Redfield ratio) is critical for coastal vegetation productivity and has an optimum value of 106:16:1. While nutrient availability around most mangroves across the globe has changed because of anthropogenic activities, it is projected to further deteriorate in the future augmenting anthropogenic stress on mangroves. The physiological mechanism of mangrove’s resistance to extreme events and changing nutrient supply is poorly understood. The present study fills this gap by advancing our understanding of the dynamics of Sundarbans mangroves in South Asia under climate extremes and changing soil nutrient composition.

How to cite: Chauhan, T. and Ghosh, S.: Dynamics of Sundarbans mangroves under climate extremes and changing soil nutrient composition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13968, https://doi.org/10.5194/egusphere-egu23-13968, 2023.

A.251
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EGU23-14235
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Nivedita Dubey and Subimal Ghosh

Higher CO2 concentration improves vegetation's water use efficiency by CO2 fertilization effects. However, anthropogenic climate change increases temperature and thus atmospheric water demand and Evapotranspiration globally, which may cause more intense frequent agricultural and ecological droughts. India is an agriculture-dependent country, with most of the population working in the agriculture and allied sector. India is also the second-highest contributor to global greening, having two of the eight global hottest biodiversity hotspots. Studies have shown that the land-atmospheric feedbacks are strong in India, and climate drivers of Indian vegetation productivity vary from those of global tropical regions. However, the effects of changing climate on Indian vegetation are unclear. Here, using the Coupled Model Intercomparison Project, phase 6 (CMIP6) Earth System Models (ESMs), we project the changes in Indian vegetation productivity over India under Increasing CO2 concentrations. We partition the radiative and biogeochemical effects of increasing CO2 concentration and how these effects drive the changes in eco-hydrological processes over India. We also investigate the sensitivity of Indian vegetation in future drought scenarios.

How to cite: Dubey, N. and Ghosh, S.: Changes in Indian vegetation productivity under increasing CO2 concentration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14235, https://doi.org/10.5194/egusphere-egu23-14235, 2023.

A.252
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EGU23-15382
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ECS
Sigrid van Grinsven, Michael Dannenmann, Jürgen Geist, Rebecca Höß, Ingrid Kögel-Knabner, Kaiyu Lei, and Jörg Völkel

Local environments such as soils and waterways, but also landscape-scale environments such as agricultural areas, are often classified as oxic based on the dominant conditions in such systems. Still, anoxic conditions do occur within these “oxic” landscapes, their upland and lowland soils, sediments and creeks at a wide range of spatiotemporal scales, and can represent hot spots and hot moments for greenhouse gas emissions but also carbon storage due to their strongly deviating biogeochemical character.

Within the project “Bavarian landscapes under climate change”, located in the crystalline Bavarian Forest, Germany, we characterize and quantify the role of anoxic spots for greenhouse gas emissions and carbon storage at the scale of agricultural landscapes, including managed grassland and cropland soils, riparian soils and creeks including their special features such as beaver dams. Our focus is on mesoscale anoxic events, at the 1-10 m2 scale, that are the result of temporary conditions, such as flooding or fine sediment deposition. We place these mesoscale events into the context of the whole agricultural landscape and watershed, and characterize the carbon species, gaseous emissions, carbon stocks, and organic carbon degradation dynamics in the different oxic and anoxic parts of our larger system, both aquatic and terrestrial. First results indicate that the enhanced greenhouse gas emissions, but also carbon storage, can be large enough to be relevant offsets of the larger scale (whole stream, riparian zone) carbon dynamics. Ignoring these spatially or temporally relatively small events or locations in upscaling or modeling can thus lead to important underestimations of carbon storage, as well as to offsets of the greenhouse gas balance of an area.

How to cite: van Grinsven, S., Dannenmann, M., Geist, J., Höß, R., Kögel-Knabner, I., Lei, K., and Völkel, J.: The importance of meso-scale anoxic spots and events in oxic environments for carbon dynamics and greenhouse gas emissions from terrestrial, riparian and aquatic ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15382, https://doi.org/10.5194/egusphere-egu23-15382, 2023.

A.253
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EGU23-15823
Decreasing precipitation disproportionally influences ecosystem water yield, risking water supply and shifting limits of forests' survival.
(withdrawn)
Eyal Rotenberg, Fyodor Tatarinov, Jonathan Muller, and dan Yakir