BG3.18

EDI
Forest methane (CH4) and nitrous oxide (N2O) cycles

Exchange of greenhouse gases (GHGs) such as methane (CH4) and nitrous oxide (N2O) in forest ecosystems has traditionally focused on gas flux measurements from soil or between biosphere and atmosphere in the surface layer only. However, it has become evident that trees may play an important role in the net exchange of these GHGs in forests. Trees can contribute to ecosystem exchange by uptake and transport of soil-produced CH4 and N2O to the atmosphere, in-situ production and consumption of both gases in plant tissues, and alternation of carbon- and nitrogen-turn-over in adjacent soil. However, the contribution of these individual processes to the net ecosystem GHGs exchange is still unclear and seems to depend on many aspects as tree species, forest ecosystem type, environmental parameters and seasonal dynamics. Interactions between soil, vegetation and the atmosphere exert a crucial role controlling the global budget of these gases.
This session seeks to bring together scientists working on the exchange of CH4 and N2O in forest ecosystems at any relevant scale, and from the full climatic and hydrological forest range. We therefore welcome contributions on (i) production and consumption processes in soils and plant tissues; (ii) gas transport processes in soil-tree-atmosphere continuum; (iii) gas flux measurements on the forest floor, cryptogams, tree stems or at leaf and canopy level; (iv) micrometeorological measurements using flux towers, satellite, or modelling approaches that seek to integrate our understanding of CH4 and N2O exchange in forest ecosystems.

Public information:

Dear colleagues and friends,

We are going to have a session dinner together on Wednesday, May 25 2022, from 8 p.m.

at the Brandauers Bierbögen (https://www.bierig.at/bierbogen/; The tables are reserved on Martin Maier).

The session dinner will be together with our colleagues from the session

SSS8.3 "Soil gases : production, consumption and transport processes".

We are looking forward to meeting you all in Vienna or online next week.

Katerina, Josep and Jukka

 

 

 

 

Co-organized by SSS9
Convener: Katerina Machacova | Co-conveners: Josep BarbaECSECS, Jukka Pumpanen
Presentations
| Wed, 25 May, 13:20–14:50 (CEST)
 
Room 3.16/17
Public information:

Dear colleagues and friends,

We are going to have a session dinner together on Wednesday, May 25 2022, from 8 p.m.

at the Brandauers Bierbögen (https://www.bierig.at/bierbogen/; The tables are reserved on Martin Maier).

The session dinner will be together with our colleagues from the session

SSS8.3 "Soil gases : production, consumption and transport processes".

We are looking forward to meeting you all in Vienna or online next week.

Katerina, Josep and Jukka

 

 

 

 

Presentations: Wed, 25 May | Room 3.16/17

Chairpersons: Katerina Machacova, Josep Barba
13:20–13:25
13:25–13:35
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EGU22-8813
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solicited
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Highlight
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Virtual presentation
Sylvia Toet, Ruochan Ma, Will Barrop, Ben Keane, James Stockdale, Roxane Andersen, Russell Anderson, Niall McNamara, Georgios Xenakis, Sirwan Yamulki, and James Morison

Forests are often considered to be able to play a significant role in tackling global warming. To fully understand their potential in mitigating climate change and to develop more accurate ecosystem GHG flux budgets and process-based models of forests, we require more knowledge of methane (CH4) and nitrous oxide (N2O) exchange in forests, their underlying processes, environmental controls and responses to forest management. In recent years, it is becoming evident that not only soils but also the trees themselves may significantly contribute to CH4 and N2O fluxes in forest ecosystems.

Our research mainly focussed on greenhouse gas (GHG) exchange in temperate UK forests on both mineral and organic soils. We will primarily concentrate on CH4 fluxes as N2O fluxes were often relatively low in these forests and, by including CO2 fluxes, we will put them into the context of the overall ecosystem GHG exchange. A range of flux methods at different scales were used in our field studies to be able to capture the often high temporal and spatial variability of the GHG exchange between the atmosphere and either soils, tree stems or entire trees aboveground, and to identify potential drivers of the fluxes. The impact of management practices including clear fell, drainage and the resulting micro-topography, and forest-to-bog restoration on CH4 fluxes from organic soils following the first forest rotation will also be described. We regularly used novel automated and chamber approaches and technologies, and the advantages and limitations of the different flux approaches and their use to upscale fluxes to the landscape scale will be evaluated.

How to cite: Toet, S., Ma, R., Barrop, W., Keane, B., Stockdale, J., Andersen, R., Anderson, R., McNamara, N., Xenakis, G., Yamulki, S., and Morison, J.: Greenhouse gas exchange in temperate forest ecosystems in the UK - A quest for key components and drivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8813, https://doi.org/10.5194/egusphere-egu22-8813, 2022.

(Hemi-)boreal zone
13:35–13:41
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EGU22-3922
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ECS
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On-site presentation
Lukas Kohl, Salla Tenhovirta, Markku Koskinen, Anuliina Putkinen, Marjo Patama, Tatu Polvinen, Ivan Marmarella, T. Matthew Robson, Maria Dominguez, Bartosz Adamczyk, and Mari Pihlatie

Methane production in plant foliage under aerobic conditions remains a cryptic and poorly constrained component of the global methane cycle. While several in-vitro studies reported light-dependent production of methane from plant biomolecules, thus far no studies have investigated methane fluxes at plant shoots during diel cycles. Here, we show that methane emissions from Scots pine shoots follow a distinct diurnal pattern and we demonstrate how these cycles allow estimating an upper limit of shoot methane emissions from ecosystem-atmosphere methane fluxes measured by the eddy covariance method. We present data from three measurement campaigns in forest, garden, and greenhouse settings that quantified methane fluxes of the shoots of Scots pine saplings and adult trees using manual and automated shoot chamber flux measurements systems, two distinct of trace gas analysers (Los Gatos Research UGGA, Picarro G2301). Despite the methodological differences, all campaigns found average methane flux rates between 0.05 and 0.20 nmol g-1 foliar dry weight h-1 in all campaigns. In the garden and greenhouse campaigns, where 24-hour measurement campaigns were possible, shoot methane fluxes exhibited pronounced diurnal cycles with a strong light dependent emission during daytime and low fluxes (mostly below the detection limit) during nighttime. Based on these strong light-dependent diurnal cycles, we were able to calculate an upper limit for shoot methane emissions at the ecosystem level. For this, we quantified the light-dependent and light-independent components of ecosystem-atmosphere methane fluxes measured by eddy covariance, with the light-dependent component tentatively indicating shoot-level methane fluxes. The monthly averages of the so-quantified light-dependent component accounted for 0.0-0.4 nmol methane m-2 sec-1 (range of monthly averages), which corresponds to ~0-1 nmol methane g-1 foliar dry weight h-1. This component is approximately 10-fold higher than shoot-level fluxes, indicating that other processes beside shoot emissions may contribute to light-dependent methane emissions. Nevertheless, even this higher estimate of shoot methane emissions correspond with the low end of the range reported by Keppler et al. (2006; 0.75–55 nmol g-1 d.w. h-1) and fall within the range reported by Fraser et al. (2015; 0.03–2 nmol g-1 d.w. h-1). Taken together, our results show how combining shoot and ecosystem level measurements can help constraining shoot emissions sufficiently for incorporating these fluxes in regional and global methane budgets. Taken together, our results show how combining shoot and ecosystem level measurements can help constraining shoot emissions sufficiently for incorporating these fluxes in regional and global methane budgets.

References:

Keppler, F., Hamilton, J., Braß, M. et al. Methane emissions from terrestrial plants under aerobic conditions. Nature 439, 187–191 (2006). https://doi.org/10.1038/nature04420

Fraser, W. T., Blei, E., Fry, S. C., et al.. Emission of methane, carbon monoxide, carbon dioxide and short-chain hydrocarbons from vegetation foliage under ultraviolet irradiation. Plant, cell & environment, 38(5), 980–989 (2015). https://doi.org/10.1111/pce.12489

How to cite: Kohl, L., Tenhovirta, S., Koskinen, M., Putkinen, A., Patama, M., Polvinen, T., Marmarella, I., Robson, T. M., Dominguez, M., Adamczyk, B., and Pihlatie, M.: Shoot methane emissions follow pronounced diurnal cycles that allow constraining aerobic methane production at the ecosystem-level, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3922, https://doi.org/10.5194/egusphere-egu22-3922, 2022.

13:41–13:47
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EGU22-11466
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Presentation form not yet defined
Mari Pihlatie, Lukas Kohl, Elisa Vainio, Anas Emad, Lukas Siebicke, Ivan Mammarella, and Katerina Machacova

The role of boreal upland forests in the global methane cycle remains poorly constrained. While chamber-based measurements clearly show that the soils of upland forest act as methane sinks, micrometeorological measurements indicate that the same forests are methane-neutral at the ecosystem level. We conducted a measurement campaign covering soil, tree stem, tree shoot, and ecosystem-level flux measurements to test whether upscaled methane fluxes from tree stems and shoots can close the observed gap between the soil and ecosystem fluxes.

The campaign was conducted in a Scots pine dominated upland forest in southern Finland at the SMEAR II Hyytiälä research station between July 1 - Aug 15 2017. It included weekly measurement of methane fluxes at 15 soil locations, 47 stem chambers at the three tree species (Pinus sylvestris, Picea abies, Betula sp.), and 6 shoot chambers, as well as micrometeorological measurement of methane fluxes at 23 m height with two methods, eddy covariance (EC) and true eddy accumulation (TEA). Soil and stem methane fluxes were further upscaled based on a topographical statistical model (Vainio et al., 2021).

Our results show a persistent gap between chamber- and micrometeorological flux measurements. While the soil acted as a moderate methane sink (-1.71 nmol m-2 s-1 ,95% confidence interval -2.03 to -1.39), micrometeorological measurements indicated that the forest was near methane neutral (EC: -0.29±0.24 nmol m-2 s-1; TEA: -0.25±0.16 nmol m-2 s-1). Spatial heterogeneity was a significant factor for soil methane uptake, as the median methane location in the tower footprint showed an approximately 0.5 nmol m-2 s-1 greater uptake than the footprint average. Methane exchange from stems (-0.035 to 0.083 nmol m-2 ground area s-1) and shoots (0.025 to 0.075 nmol m-2 ground area s-1) were at least an order of magnitude smaller than the gap between the soil and ecosystem measurements. While these estimates are associated with significant uncertainties primarily stemming from the upscaling model, it is unlikely that the stem and shoot fluxes act as the missing methane source in this ecosystem.

Overall, results indicate that the gap between soil and ecosystem fluxes results either from a systematic error in micrometeorological flux measurements or from too high uncertainties related to measured fluxes very close to the detection limit of the EC/TEA system. It is also possible that an unidentified methane source exists in these forests. We were, for example, not able to conduct shoot flux measurements at moist sites within the flux tower footprint. We further note that our campaign was conducted during the peak summer months when stem and soil fluxes are expected to be relatively small due to low soil moisture. Nevertheless, our data suggests that a difference between trace gas fluxes at the soil and ecosystem level are not necessarily indicative of stem or canopy processes, and that such differences need to be interpreted with great care.

References:

Vainio, E., Peltola, O., Kasurinen, V., Kieloaho, A.-J., Tuittila, E.-S., Pihlatie, M.: Topography-based statistical modelling reveals high spatial variability and seasonal emission patches in forest floor methane flux, Biogeosciences, 18, 2003–2025, https://doi.org/10.5194/bg-18-2003-2021, 2021.

How to cite: Pihlatie, M., Kohl, L., Vainio, E., Emad, A., Siebicke, L., Mammarella, I., and Machacova, K.: Can tree stem and shoot emissions close the gap in the methane budget of a boreal Scots pine forest during the summer months?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11466, https://doi.org/10.5194/egusphere-egu22-11466, 2022.

13:47–13:53
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EGU22-11588
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Presentation form not yet defined
Salla Tenhovirta, Lukas Kohl, Markku Koskinen, and Mari Pihlatie

Plants can emit methane (CH4) produced by an unknown aerobic, non-enzymatic process, driven by plant stressors like UV-radiation, elevated temperatures and wounding. In ambient spring conditions in Finland, CH4 emissions from the shoots of Scots Pine (Pinus sylvestris) correlated with solar radiation independently of temperature (Tenhovirta et al., in revision). The spring-time shoot CH4 emissions also had a diurnal pattern with the highest emissions during noon. It remains unknown whether these emissions are driven directly by solar radiation or indirectly via its effect on tree physiological processed such as photosynthesis or stomatal conductance. Characterizing the ecophysiology of the CH4 fluxes of tree canopies is a crucial step in order to understand the role of forests in the global CH4 cycle.

To test whether shoot CH4 emissions are driven by tree physiological activity (e.g. stomatal conductance), we conducted a measurement campaign in greenhouse conditions during which Scots pine saplings were exposed to drought. During this 3-month-long campaign, CH4, carbon dioxide (CO2) and water vapour (H2O) fluxes from tree shoots were measured with an automated shoot trace gas flux measurements system (ShoTGa-FluMS)(Kohl, Koskinen et al., 2021). This system is capable of replacing the CO2 assimilated by the shoots, removing transpired water and cooling the chambers to near ambient temperatures. The experimental setup consisted of six 2-3 year old nursery saplings each with a shoot enclosed inside an automated shoot chamber, alternating (a) in closed loop with a Picarro G2301 cavity ring-down spectroscopy (CRDS) greenhouse gas concentration analyser (CH4 and CO2 measurements), (b) in a flow-through setup with a Li-cor 850 CO2-H2O analyser (photosynthesis and transpiration measurements), or (c) flushed with ambient air. The saplings were exposed to a daily 9-hour photoperiod of ~ 600-800 µmol s-1 m-2 photosynthetically active radiation (PAR), and irrigated automatically. Drought was induced by stopping the irrigation and continued to the point where net uptake of CO2 no longer occurred.

Our experiment produced a unique dataset of continuous measurements of shoot-level CH4, CO2 and H2O fluxes over a period of several weeks. Our preliminary results show small but consistent CH4 emissions from the shoots of Scots Pine during daylight, supporting our earlier findings of the dependency of shoot CH4 emissions on light. The data furthermore allows to analyse the effects of drought on tree physiological activity and shoot CH4 fluxes providing much needed process understanding of shoot CH4 emissions from boreal trees.

References

Kohl, Koskinen et al. 2021. An automated system for trace gas flux measurements from plant foliage and other plant compartments. Atmospheric Measurement Techniques 14: 4445–4460.

How to cite: Tenhovirta, S., Kohl, L., Koskinen, M., and Pihlatie, M.: Effects of drought on the methane emissions of the shoots of young scots pine saplings , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11588, https://doi.org/10.5194/egusphere-egu22-11588, 2022.

13:53–13:59
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EGU22-7763
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ECS
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On-site presentation
Methane flux changes during irrigation experiment in boreal upland forest soil - lessons for future experiments
(withdrawn)
Tiia Määttä, Annalea Lohila, Miska Luoto, Mika Korkiakoski, and Timo Penttilä
13:59–14:05
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EGU22-7061
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ECS
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On-site presentation
Carl-Fredrik Johannesson, Klaus Steenberg Larsen, and Jenni Nordén

Methane (CH4) is the second largest contributor to global warming and the importance of reducing CH4 emissions was recently highlighted through the Global Methane Pledge launched in 2021. Forest soils can act both as sinks and sources of CH4, largely depending on the hydrological status of the soil, and both direction and magnitude of CH4 fluxes often vary considerably even across small spatial and temporal scales. Thus, projected changes in precipitation patterns can be expected to affect both total CH4 budgets and the spatiotemporal distribution of sinks and sources. Forest management – for example clear cutting and nitrogen (N) fertilization – also affects CH4 cycling in forests with the potential to turn CH4 sinks into CH4 sources, but little is currently known about the mechanisms and to what extent fluxes are affected by forest management.

In the ForBioFunCtioN project, we have set up an extensive climate and management manipulation experiment across five Norwegian spruce dominated bilberry forest sites spanning from a recent clear-cut to mature managed (80 years) and old unmanaged (140 years) stands. Treatments include warming with open-top chambers, simulated increased precipitation and additions of N fertilizer and biochar in a total of 12 different treatment combinations (n = 144). We utilize state-of-the-art technology (LI-7810 Trace Gas Analyzer, LI-COR®) for measurements of soil-atmosphere and deadwood-atmosphere exchange of CO2 and CH4.

Here, we present the experimental setup and soil and deadwood flux measurements of CO2 and CH4 from June to December 2021. Initial results show that soil CH4 fluxes vary considerably both between and within sites yet indicate short-term responses of CH4 fluxes to addition of biochar and N fertilizer in particular.

How to cite: Johannesson, C.-F., Larsen, K. S., and Nordén, J.: Forest soil and deadwood CH4 fluxes in response to climate change and forest management, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7061, https://doi.org/10.5194/egusphere-egu22-7061, 2022.

14:05–14:11
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EGU22-7493
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ECS
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On-site presentation
Reti Ranniku, Thomas Schindler, Jordi Escuer-Gatius, Ülo Mander, Katerina Machacova, and Kaido Soosaar

Peatland soils are considered the dominating source of methane (CH4) and nitrous oxide (N2O) to the atmosphere. However, there are high spatio-temporal uncertainties regarding the soil greenhouse gas (GHG) fluxes due to complex dynamics between the soil chemical, physical and biological variables. Although GHG fluxes from peatland soils are relatively well studied, tree stem fluxes have received far less attention and are often overlooked in GHG models and assessments. Moreover, simultaneous year-long measurements of soil and tree stem CH4 and N2O fluxes in peatland forests are missing, as previous studies have primarily focused on the growing season. We aim to determine the seasonal dynamics of CH4 and N2O fluxes in drained peatland forests, as drainage can lead to release of the large amounts of carbon and nitrogen stored in peat into the atmosphere as GHGs.

Our research focuses on tree stems and soil GHG fluxes in the Agali Drained Peatland Forest Research Station in Estonia, dominated by Downy Birch (Betula pubescens) and Norway Spruce (Picea abies) trees. During the weekly sampling campaigns (November 2020–December 2021), we used manual static stem chambers to collect gas samples, which were later analysed for CH4 and N2O in the laboratory using Shimadzu GC-2014 gas chromatography. We measured soil CH4 and N2O fluxes using an automated dynamic soil chamber system connected to a Picarro G2508 analyser.

Preliminary results show that on average, birch stem GHG fluxes were greater than spruce stem fluxes. Birch trees were a net annual source of both CH4 (0.38 ± 0.09 µg C m-2 stem area h-1, mean ± SE) and N2O (0.94 ± 0.32 µg N m-2 h-1). Spruce trees were a net source of CH4 (0.08 ± 0.05 µg C m-2 h-1) but a net sink of N2O (–0.08 ± 0.02 µg N m-2 h-1). Temporal dynamics of birch stem CH4 emissions were characterised by significant emission peaks in November and June. During the rest of the year smaller fluxes with fluctuations between emissions and uptake were observed. Spruce stem CH4 fluxes followed a roughly similar pattern as birch fluxes. However, during the birch emission peak in June, spruce stems showed uptake of CH4. Birch stem N2O emissions remained very small for most of the year, with increased emissions in autumn months and March. Spruce stem N2O fluxes remained very low throughout the year.

Soils were a net annual sink of CH4 (–6.44 ± 0.76 µg C m-2 ground area h-1) and source of N2O (41.68 ± 3.15 µg N m-2 h-1). CH4 was taken up by the soil most of the year, however occasional emissions occurred. A substantial increase in CH4 uptake was observed in June, peaking at –49.53 µg C m-2 h-1 at the end of July, and diminishing towards the end of summer. Hot moments – notably higher daily average emissions compared to the period average – characterised the temporal dynamics of soil N2O emissions.

Further results on soil meteorological and biogeochemical properties will help determine the possible drivers of stem and soil fluxes’ dynamics and their origin.

How to cite: Ranniku, R., Schindler, T., Escuer-Gatius, J., Mander, Ü., Machacova, K., and Soosaar, K.: Greenhouse Gas Dynamics in a Drained Peatland Forest: Annual CH4 and N2O Fluxes from Tree Stems and Soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7493, https://doi.org/10.5194/egusphere-egu22-7493, 2022.

Temperate zone
14:11–14:17
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EGU22-6985
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ECS
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Virtual presentation
Natalia Kowalska, Adam Bednarik, and Georg Jocher

Freshwaters (rivers, streams, ponds, reservoirs) are a well-recognized source of methane (CH4) characterised by large spatiotemporal variability. However, the determination of the role of water bodies for net CH4 exchange on forest ecosystem scale is very scarce. Our study aimed to determine the importance of individual emission pathways for total CH4 fluxes from streams and to verify the possible identification and quantification of CH4 fluxes from water bodies on the floodplain forest ecosystem level. In 2020, we measured CH4 fluxes by diffusion and ebullition from a lowland stream flowing through the lowland broadleaf mixed temperate forest at Lanžhot in the Czech Republic (Central Europe). For this purpose, 18 bubble traps were installed at three stream sites and periodically sampled for gas volume and its CH4 content from April to December. Diffusive CH4 fluxes from water were measured at 14 days intervals with a floating chamber connected to a portable GHG analyser. Simultaneously, CH4 exchange was determined on the forest ecosystem scale using the eddy covariance method (EC). We hypothesized initially that due to a relatively small area of water bodies in the EC footprint and a high probability of CH4 consumption by soils, CH4 emissions will be detectable by EC only in case that water bodies will create the potential CH4 emission hotspots in the studied ecosystem. We found that the investigated stream was a significant source of CH4 (mean 260 ± 107 mg CH4 m-2 day-1) with ebullition as a dominant pathway (55 – 85%) of CH4 release throughout the whole monitored time period. Furthermore, first EC results showed that the whole ecosystem is a small but constant CH4 source as we observed an average emission flux of 16 ± 18 mg CH4 m-2 day-1 over the period June to November 2021. In-depth investigations of the potential CH4 sources and sinks within the studied ecosystem should answer the question of how the relative proportion of water surfaces and related CH4 emission corresponds to whole ecosystem CH4 fluxes.

How to cite: Kowalska, N., Bednarik, A., and Jocher, G.: Quantification of methane fluxes from water bodies on the floodplain forest ecosystem level, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6985, https://doi.org/10.5194/egusphere-egu22-6985, 2022.

14:17–14:23
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EGU22-12003
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On-site presentation
Josep Barba, Giulio Curioni, and Vincent Gauci

Tree stems emit CO2 and can exchange CH4 with the atmosphere (either emitting or uptaking), with a significant contribution to the C budgets from local to regional scales. However, there is still a need to better understand the spatial and temporal variability of stem CO2 and CH4 fluxes to quantify the role of vegetation on the C cycle and how these fluxes will behave under future environmental conditions such as atmospheric elevated CO2. An increment of atmospheric CO2 concentrations might result in higher photosynthetic rates, which would spin the C cycle in the trees, potentially increasing stem CO2 emissions due to higher stem respiration and higher soil-derived CO2 contribution. Higher photosynthetic rates might also stimulate fine roots exudation, which could stimulate methanotrophic or methanogenic communities. Additionally, elevated CO2 would increase water use efficiency at the leaf level, reducing the amount of water transpired, and potentially increasing soil moisture, which would favour conditions for CH4 production. In this study, we present one year of monthly measurements of stem CO2 and CH4 fluxes from mature oaks (Quercus robur) growing under elevated CO2 (~150 ppm above atmospheric concentrations) and ambient conditions, in a second-generation FACE experiment (Free Air CO2 Enrichment; BIFoR-FACE UK). Trees growing under ambient conditions emitted 76% more CO2 than those under elevated atmospheric CO2, which was not what we hypothesized. Despite stem CH4 fluxes have been reported in multiple upland ecosystems for lots of tree species, our preliminary results did not show clear evidence of CH4 stem fluxes (emissions or uptake) for the oaks at our study site. Similar measurements in other FACE experiments are needed to determine if our results on the effect of elevated CO2 on stem CO2 and CH4 fluxes could be extrapolated to other ecosystems and species. 

How to cite: Barba, J., Curioni, G., and Gauci, V.: Temporal and spatial effects of elevated CO2 on greenhouse gas fluxes from tree stems in an upland temperate forest, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12003, https://doi.org/10.5194/egusphere-egu22-12003, 2022.

14:23–14:29
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EGU22-4171
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On-site presentation
Katerina Machacova, Thomas Schindler, Ülo Mander, Kaido Soosaar, and Thorsten E. E. Grams

Besides soils, tree stems are known to emit nitrous oxide (N2O) into the atmosphere. However, it seems, stems of some tree species might also take up this important greenhouse gas from the atmosphere under certain conditions. Even though tree leaves dominate the tree surface area, they are entirely excluded from field N2O flux measurements, and their role in forest N2O exchange is still unknown.

We aimed to investigate the contribution of leaf fluxes to the forest N2O exchange. We determined N2O exchange of stems and leaves of mature European beech (Fagus sylvatica), and adjacent soil in a typical temperate upland mixed forest in Southern Germany, using non-steady-state chamber methods and a system of scaffold towers reaching the top of tree crowns in 35 m. The measurements were accompanied by a parallel determination of stem, leaf and soil CO2 exchange and numerous environmental characteristics (soil N2O and CO2 concentrations and water content in vertical soil profiles, soil and air temperature).

We found out that the beech stems and especially the leaves were net sinks of N2O from the atmosphere (–1.07 ± 3.47 and –249.9 ± 84.3 mg N2O ha−1 ground area h−1, respectively), whereas the soil was a net N2O source into the atmosphere (24.0 ± 10.8 mg N2O ha−1 h−1). The never studied tree leaves were identified as a key player in ecosystem N2O exchange, taking up in fact 10 times more N2O than the soil emits at the same time. Therefore, native Central European and widely spread European beech trees seem to contribute to forest N2O uptake markedly.

For the first time, we revealed tree leaves being substantial N2O sinks. Our results clearly show that the current and ongoing exclusion of tree leaves from forest N2O flux measurements can lead to a severe underestimation of the overall tree and forest N2O exchange and, therefore, global forest greenhouse gas flux inventories.

 

Acknowledgement

This research was supported by the Czech Science Foundation (17-18112Y) and project SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797). We thank Jan Hrdlička and Thomas Feuerbach for their technical support.

 

 

How to cite: Machacova, K., Schindler, T., Mander, Ü., Soosaar, K., and Grams, T. E. E.: Leaves of mature European beech consume nitrous oxide (N2O) from the atmosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4171, https://doi.org/10.5194/egusphere-egu22-4171, 2022.

(Sub-)tropical zone
14:29–14:35
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EGU22-3300
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ECS
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Virtual presentation
Luke Jeffrey, Charly Moras, Douglas Tait, Mitchell Call, Dylan Laicher, James Sippo, Scott Johnston, and Damien Maher

Tree stem methane emissions are gaining rapid research momentum, with about one-third of all literature in this field published in 2021 alone. Long term and seasonal studies are currently rare, limiting our ability to constrain spatial and seasonal emissions variability, and to resolve the tree stem contribution to the total wetland methane flux i.e. soil, water and trees. Here we present preliminary methane flux data from a lowland Melaleuca quinquenervia forest. We measured emissions in situ along a ~3 m amplitude topo-gradient, encompassing forest in lower, transitional and upper elevation zones. Eight (ongoing) field campaigns at monthly intervals, captured flooded to dry to re-flooded site conditions. We measured the stem fluxes from 30 trees at four stem heights, along with 30 adjacent soil and water CH4 fluxes. Ancillary parameters such as pore water (CH4, DO%, pH, temp, redox, EC), water table depth, and soil moisture (VWC %) were also measured. Tree stem fluxes ranged several orders of magnitude between hydrological seasons and topo-gradient zones (ranging from negligible to 17, 426 mmol ha-1 d-1). Soil fluxes were similar in amplitude and shifted from maximal CH4 emissions during the wet conditions, to CH4 uptake in dry locations. The importance of tree stem flux to the net ecosystem flux (NEF) differed between campaigns and hydrological zones, but were most substantial during flooded conditions and ranged from 36-75% of the NEF in the lower and transitional zones during peak emissions respectively. In the upper zone, the tree stem emissions offset the soil sink capacity by ~50% when the water table was closest to the soil surface. This study shows the importance of quantifying lowland tree stem CH4 emissions to the total wetland flux. This data provides important baseline readings for southern hemisphere and Australian wetland forests, that generally experience dynamic rainfall and soil redox oscillations between flooding and droughts.

How to cite: Jeffrey, L., Moras, C., Tait, D., Call, M., Laicher, D., Sippo, J., Johnston, S., and Maher, D.: How important are annual tree stem methane emissions to the total wetland flux? A seasonal case study of subtropical lowland Melaleuca forest., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3300, https://doi.org/10.5194/egusphere-egu22-3300, 2022.

14:35–14:41
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EGU22-12685
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On-site presentation
Luana Basso, Luciana Gatti, Luciano Marani, John Miller, Manuel Gloor, John Melack, Henrique Cassol, Graciela Tejada, Lucas Domingues, Egidio Arai, Alber Sanchez, Sergio Corrêa, Liana Anderson, Luiz Aragão, Caio Correia, Stephanie Crispim, and Raiane Neves

After a period where atmospheric methane (CH4) levels were nearly steady, its levels have been rapidly raising since 2007, but the main reasons remains uncertain. Increases in wetlands emissions could be one possible reason, mainly at tropical regions like Amazonia, which host some of the largest wetlands/seasonally flooded areas on the globe. Based on 590 lower troposphere vertical profiles of CH4 and carbon monoxide (CO) observations over four sites at Amazon (at the northeast, southeast, northwest-central and southwest-central regions) we estimated that Amazon region contributes with 8% of global CH4 emissions, and wetlands are the mainly CH4 source to the atmosphere (Basso et al., 2021). Vertical profiles are sampled using light aircraft, high-precision greenhouse gas and CO analysis of flask air, fortnightly between 2010 and 2018. We observed an unexpected east-west gradient in CH4 emissions, with higher emissions in northeast Amazon region. The higher emissions are mainly from wetlands and are not explained by biomass burning and anthropogenic emissions (like enteric fermentation), but its causes remains unclear. In the other three sites located further downwind along the main air-stream the CH4 emissions represents approximately 24-36% of what is observed in the northeast region. Our wetlands emission estimates of each region were compared to analogous fluxes from the WetCharts wetland model ensemble (Bloom et al., 2017). The estimates were similar except for the northeast region, where WetCharts does show substantial emissions, but still just 40% of our estimates based on the lower troposphere observations (Basso et al., 2021).

How to cite: Basso, L., Gatti, L., Marani, L., Miller, J., Gloor, M., Melack, J., Cassol, H., Tejada, G., Domingues, L., Arai, E., Sanchez, A., Corrêa, S., Anderson, L., Aragão, L., Correia, C., Crispim, S., and Neves, R.: Regional variability in Amazon methane emissions based on lower-troposphere observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12685, https://doi.org/10.5194/egusphere-egu22-12685, 2022.

Climate gradient
14:41–14:47
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EGU22-13360
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On-site presentation
Vincent Gauci, Sunitha Pangala, Alexander Shenkin, Josep Barba, David Bastviken, Viviane Figueiredo, Carla Gomez, Alex Enrich-Prast, Emma Sayer, Tainá Stauffer, Bertie Welch, Myles Allen, and Yadvinder Malhi

Forests play an important role in the exchange of radiatively important gases with the atmosphere. Previous studies have shown that in both temperate and tropical wetland forests tree stems are significant sources of methane, yet little is known about tree stem trace greenhouse gas dynamics in drier, free-draining soils that dominate global forested areas. Here, we examine methane fluxes on tree stems spanning a climate gradient of upland forests and floodplain forest across 4 locations in the Amazon, Brazil (Cunia, Rios Negro, Solimoes and Tapajos), lowland tropical forest on free-draining soils in Panama, Central America (Barro Colorado Nature Monument), deciduous woodland in the United Kingdom (Wytham, Oxfordshire) and boreal forest in Sweden. We found that trees behaved as both methane sources (near the tree base) and sinks (higher up the tree stem) across tropical, temperate and boreal sites and are highly variable, yet we were able to identify a broad correlation between the size of tree stem methane uptake fluxes and mean annual temperature across the climate gradient. The vertical spatial patterns of flux up the individual measured trees and climate gradient temperature-methane flux relationship together with revised LiDAR derived tree surface allometry permitted global scaling of fluxes in upland forest. Results of this scaling together with the implications of this refined understanding of the global methane cycle under various scenarios are discussed.

How to cite: Gauci, V., Pangala, S., Shenkin, A., Barba, J., Bastviken, D., Figueiredo, V., Gomez, C., Enrich-Prast, A., Sayer, E., Stauffer, T., Welch, B., Allen, M., and Malhi, Y.: Methane source-sink behaviour in upland trees spanning a global climate gradient, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13360, https://doi.org/10.5194/egusphere-egu22-13360, 2022.

14:47–14:50