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Amazon forest – a natural laboratory of global significance

The Amazon forest is the world’s largest intact forest landscape. Due to its large biodiversity, carbon storage capacity, and role in the hydrological cycle, it is an extraordinary interdisciplinary natural laboratory of global significance. In the Amazon rain forest biome, it is possible to study atmospheric composition and processes, biogeochemical cycling and energy fluxes at the geo-, bio-, atmosphere interface under near-pristine conditions for a part of the year, and under anthropogenic disturbance of varying intensity the rest of the year. Understanding its current functioning at process up to biome level in its pristine and degraded state is elemental for predicting its response upon changing climate and land use, and the impact this will have on local up to global scale.
This session aims at bringing together scientists who investigate the functioning of the Amazon and comparable forest landscapes across spatial and temporal scales by means of remote and in-situ observational, modelling, and theoretical studies. Particularly welcome are also presentations of novel, interdisciplinary approaches and techniques that bear the potential of paving the way for a paradigm shift.

Convener: Laynara F. LugliECSECS | Co-conveners: Eliane Gomes-AlvesECSECS, Laëtitia Brechet, Carlos Alberto Quesada
Presentations
| Tue, 24 May, 15:55–18:25 (CEST)
 
Room 2.95

Tue, 24 May, 15:10–16:40

Chairpersons: Laynara F. Lugli, Eliane Gomes-Alves

15:55–15:58
Brief welcome and introduction to the session structure (Basin wide patterns)

15:58–16:08
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EGU22-1203
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solicited
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Highlight
Paulo Artaxo et al.

Amazonia is under significant stress from both deforestation and climate change. Multiple pieces of evidence show that the links between the hydrological and carbon cycles are fast changing. Deforestation is increasing in Amazonia, and in 2021, about 13,35 km² of forests were converted, a value 22% larger than 2020. On the deforestation side, the government's recent public policies favor illegal occupation of public lands and invasion of indigenous territories protected by the Brazilian constitution. Deforestation brings forest degradation to the edges of deforested areas, increasing carbon emissions. The impact of climate change is less clear, with changes in the hydrological cycle and increased temperature, promoting forest degradation that makes parts of the Amazon Forest become a carbon source.

The Amazonian forest is a very complex system with multiple anthropogenic and climate change pressures. It is hard to know where a possible Amazonian tipping point could be and which variables or values could be the indicators for this possible tipping point. The role of intensified climate extremes is another critical variable, with Amazonia under increased intense droughts/inundation cycles in the last 30 years. Remote sensing measurements show that vapor pressure deficit is increasing for both perturbed Eastern and at the pristine Northern Amazonia. Several different studies show that the carbon uptake by undisturbed forests is not equilibrating the carbon emissions by deforestation for parts of Amazonia. CO2 emissions associated with deforestation are increasing. The MapBiomas system provides detailed land-use change maps linked to meteorological information to apportion carbon emissions to forest degradation or deforestation. The role of soil emissions is not fully quantified for the overall Amazonia. We are developing a basin-wide system using big data strategies with machine learning, artificial intelligence, and other advanced techniques to address drivers for land-use changes in Amazonia and carbon and methane emissions and sinks. Flooded areas in Amazonia show significant methane emissions, and the effects of increasing floods and droughts cycles have an important impact on methane emissions. First results will be presented, with CO2 and CH4 ground-based and remote sensing measurements in Amazonia, coupled with MapBiomas land-use change maps.

How to cite: Artaxo, P., Toledo Machado, L. A., Menezes Franco, M. A., Barbosa de Albuquerque, I. M., Rizzo, L. V., Shimbo, J., Alencar, A., Trumbore, S., and Silva, J. R.: Deforestation and climate change: The multiple pressures over Amazonian forests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1203, https://doi.org/10.5194/egusphere-egu22-1203, 2022.

16:08–16:15
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EGU22-8935
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ECS
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Highlight
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Chandrakant Singh et al.

The tropical terrestrial ecosystems naturally exist as alternative stable states, commonly referred to as forest and savanna ecosystems. However, these ecosystems, especially forests, are currently threatened by the risk of drought-induced forest-to-savanna transitions across the tropics and subtropics. Therefore, a better understanding of ecosystem dynamics and characteristics behind these alternative stable states is crucial in predicting their response to future hydroclimatic changes. Previous studies have analyzed these alternative stable states against precipitation predominantly based on space-for-time substitution. However, such a substitution provides a partial picture of ecosystem adaptation dynamics and associated ecosystem structural change over time. 

Here, we empirically study the transient state of tropical ecosystems and their hydroclimatic adaptations by examining remotely sensed tree cover and root zone storage capacity over the last two decades in South America and Africa. Tree cover represents the above-ground ecosystem structure's density, and is derived directly from MODIS satellite data. Whereas root zone storage capacity is the maximum amount of soil moisture that the vegetation can access for transpiration is derived using daily precipitation and evaporation data. 

We found that ecosystems at high (>75%) and low (<10%) tree cover adapt to changing precipitation by instigating considerable subsoil investment while experiencing limited tree cover change over time. For these ecosystems, the below-ground investment does not come at the cost of changing the above-ground ecosystem structure. Thus, we deem these ecosystems as stable since ecosystems' adaptive dynamics keep the structural characteristics intact. In contrast, unstable ecosystems at intermediate (30-60%) tree cover were unable to exploit the same level of adaptation as stable ecosystems, thus showing considerable changes to their above-ground ecosystem structure. We also found that ignoring this adaptive capacity of the ecosystem can underestimate the resilience of the forest ecosystems, which we find is largely underestimated in the case of the Congo rainforests. The results from this study emphasize the importance of the ecosystem's temporal dynamics and adaptation in inferring and assessing the risk of forest-savannah transitions under rapid hydroclimatic change.

How to cite: Singh, C., van der Ent, R., Wang-Erlandsson, L., and Fetzer, I.: Two decades of forest monitoring shows instability in the rainforests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8935, https://doi.org/10.5194/egusphere-egu22-8935, 2022.

16:15–16:22
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EGU22-11505
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ECS
Gerbrand Koren et al.

In recent years, the Amazon forest has experienced several major droughts (2010, 2015/16) and floods (2012, 2014, 2021). Extreme events represent a threat to the Amazons important functions, but these perturbations also provide valuable insights into the underlying mechanisms. Here we studied the most recent massive drought and flood events in detail, and quantified their severity and spatiotemporal extent relative to a multi-year baseline.

First, we describe the anomalous hydrological status of these events, by bringing together a large variety of data sets, including in-situ observations and reanalysis products for precipitation, discharge, vapor pressure deficit and soil moisture. During the strong El Niño conditions following the dry season of 2015, the precipitation fell below its climatological values. This was soon reflected in low discharge rates and soil moisture levels, persisting far into the year 2016 for some regions. In contrast, we find anomalously high precipitation over the northern Amazon during the first months of 2021, resulting in high discharge rates,  and  rising river levels that have led to massive floods in downstream regions.

Finally, we quantified the impact of the 2015/16 drought on vegetation using the inverse model CarbonTacker South America (CT-SAM) and remote sensing proxies for photosynthesis. To address the uncertainty in prior emission estimates, we have used a range of different biosphere models (SiBCASA, SiB4), including a biosphere model linked to a detailed hydrological model (PCR-GLOBWB). For the fire flux we used multiple data sets (GFAS, SiBCASA-GFED4), including a modified version based on CO inversions performed with the TM5-4DVAR system. We find that photosynthesis was reduced during the 2015 drought, especially in the drier, southern part of the Amazon. This was followed by a recovery in the first months of 2016, but during the subsequent dry season a secondary impact on photosynthesis was found. The inversely derived net CO2 fluxes do not have the same high resolution as the satellite products, but when assessed over larger scales, a consistent drought signal is derived.

How to cite: Koren, G., Botía, S., Domingues, L. G., Florentie, L., Gatti, L. V., Gloor, M., Harrigan, S., Krol, M. C., Luijkx, I. T., Miller, J. B., Naus, S., and Peters, W.: Extreme droughts and floods in the Amazon forest, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11505, https://doi.org/10.5194/egusphere-egu22-11505, 2022.

16:22–16:29
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EGU22-8966
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ECS
Shujiro Komiya et al.

The vegetation and soils of the Amazon contain large amounts of carbon that may be vulnerable to loss given ongoing climate and land use change in the Amazon basin. Previous studies predicted that the Amazon rainforest would start to act as a net carbon source to the atmosphere by 2030-2040, and that it has switched from being a sink to source over the last decade. Using data from eddy covariance and vertical carbon dioxide profile measurement systems installed at the 80 m walk-up tower in the Amazon Tall Tower Observatory (ATTO) site, located in well-preserved central Amazon upland rainforest, we assessed net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco) for the period 2014-2019. The NEE results indicate that the central Amazon upland rainforest was carbon neutral or a source during this 6-year period. Seasonal GPP variations were related to soil water availability and vapor pressure deficit. The strong 2015-2016 El Niño event decreased both GPP and Reco due to the unusually long dry period, but also contributed to carbon flux dynamics in post El Niño periods. In the 2017-dry season, we measured higher dry-season GPP compared with the other years, which we hypothesize was triggered by photosynthesis activation in sub-canopy and understory trees. This is supported by the minimum green crown fraction at upper canopy trees, indicating more light availability in lower canopy trees, and the higher fraction of absorbed photosynthetically active radiation, both recorded during the dry-season of 2017. Our results show that the ground-based measurement setup at ATTO is well suited to investigate the local carbon fluxes on seasonal to interannual time scales.

How to cite: Komiya, S., Carioca de Araújo, A., V. Lavric, J., Nelson, B., Sörgel, M., Weber, B., Botia, S., Gomes-Alves, E., Walter, D., de Oliveira Sá, M., Wolff, S., M. Pinho, D., Kondo, F., and Trumbore, S.: Seasonal and interannual variations of carbon fluxes at the Amazon Tall Tower Observatory site in 2014-2019, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8966, https://doi.org/10.5194/egusphere-egu22-8966, 2022.

16:29–16:36
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EGU22-12016
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ECS
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Highlight
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Michel Valette et al.

Whilst the deforestation rate of the Brazilian Amazon has decreased drastically over the 2005-2015 period, thanks to an ambitious program to fight deforestation, since then, forest degradation resulting from logging and wildfires became the major source of aboveground biomass losses and the Brazilian Amazon turned into a net carbon source. This could be partially explained by a decoupling of fire occurrence and deforestation, historically one of the key drivers of the fire regime in the region. Moreover, since 2015, deforestation rates and associated fires are rising again, and new deforestation frontiers are opening in previously unaffected areas in the central and western Amazon.

Fires in the Brazilian Amazon are closely related to climate and agriculture: fires are used to transform forests into pastures or cropland, and subsequent burns are used to maintain grass productivity. When nearby rainforests are sufficiently dry, deforestation and agricultural fires escape and can cause large wildfires. Local communities’ fire management practices impact greatly the likelihood of these escaping fires, but also bear a cost. High mortality rates after even low-intensity fires lead to fuel accumulation and canopy damage, increasing the vulnerability of forests to subsequent burnings. Coupled with a regional reduction of precipitations due to climate change and deforestation, the Amazon forest could be threatened by a cycle of massive dieback and increased fire activity. Thus, it is crucial to understand the drivers of different types of fires in the region and how to prevent them. Of particular interest is the role played by the policies deployed after 2004 to reduce deforestation rates in the region and their recent weakening.

Building on previously published literature on the drivers of fire regimes and deforestation in the region, data were collected on potential drivers of fire regimes related to climate, agricultural expansion, ecosystem integrity, infrastructure, populations, environmental policies and land conflict. MODIS Active-Fire dataset was used as a response variable, and also classified into deforestation fires, agricultural fires and forest fires thanks to deforestation and land use data in a second step of the study. A spatiotemporal modelling approach, relying on the Log Gaussian Cox process and R-INLA package, has been adopted to assess the relative influence of different drivers of fire regimes in the Brazilian Amazon for the 2006-2020 period. Preliminary results on the drivers of fire regime in the state of Para for the last four years show a powerful influence of drivers related to agricultural expansion (especially ranching), integrity of the forest cover, presence of rural settlements and environmental policies. Different protection regimes have varying influences on the fire regime, with sustainable use areas being the less efficient. Law enforcement efforts seem to have an inhibitory effect on fire occurrence and protected area downgrading, downsizing and degazettement favour them.

How to cite: Valette, M., Mills, M., Woods, J., Kountouris, Y., and Singh, M.: Assessing social and ecological drivers of fire regimes in the Brazilian Amazon in the context of changing forest governance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12016, https://doi.org/10.5194/egusphere-egu22-12016, 2022.

16:36–16:37
Transition to smaller scale natural variations

Tue, 24 May, 17:00–18:30

Chairpersons: Laynara F. Lugli, Eliane Gomes-Alves

17:00–17:07
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EGU22-2592
Luca Mortarini et al.

A central constituent of the ATTO project  is the deployment of an array of sonic anemometers to measure vertical profiles of means and second-order moments of the wind velocity vector. The two instruments used are the Campbell Scientific Instruments CSAT-3B and the Thies Ultrasonic Anemometer 3D. The accuracy of the vertical profiles of turbulent quantities critically depensds on an absence of bias between the measurement levels; however, dedicated intercomparisons of the sonic anemometers used in ATTO have not been previously performed.  The main objective of the experiment was to check how close the sonic anemometers designated to be installed respond to the same atmospheric conditions, and to develop confidence in interpreting the measured data. 

How to cite: Mortarini, L., Dias, N., Quaresma Dias, C., Brondani, D., Acevedo, O., Manzi, A., de Oliveira, P., Tsokankunku, A., Rossato, F., Araújo, A., Soergel, M., and Nobre Quesada, C. A.: The ATTO Micrometeorological Intercomparison Experiment (ATMIX), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2592, https://doi.org/10.5194/egusphere-egu22-2592, 2022.

17:07–17:14
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EGU22-3731
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ECS
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Akima Ringsdorf et al.

The tropical rainforest is the largest source of VOCs to the global atmosphere [1], where they are oxidized primarily by the hydroxyl radical (OH) [2]. In-situ measurements of OH are rare, especially from tropical forests, but indirect OH estimates can be made using VOC concentrations measured from aircraft or towers. For this it is necessary to measure the vertical change in concentration of a specific VOC with a known OH rate coefficient, within a known reaction time. In this study volatile organic compounds (VOC) were measured on the Amazon Tall Tower Observatory (ATTO) from 3 heights (80, 150 and 325 m) above the Amazon rainforest with a PTR-TOF-MS 4000 (IONICON Analytik GmbH). Typically to estimate OH, the convective timescale of the boundary layer is taken as the approximate reaction time. However, here we have developed a new method to determine the vertical transport based on the dynamic time warping technique. Median averaged transport times from 80 m to 325 m ranged from 105 to 15 minutes with decreasing values throughout the day from 06:00 to 15:00 as thermal and shear driven convection increases. We apply this method to determine effective OH concentrations between 80-325 m using isoprene and its oxidation products (methyl vinyl ketone, methacrolein and ISOPOOH) and compare these empirically derived values to values from the large-eddy simulation DALES [3]. The timescales of turbulent mixing and OH chemistry are similar, so both govern the vertical change in concentration.

[1] Guenther, Alex. “Biological and Chemical Diversity of Biogenic Volatile Organic Emissions into the Atmosphere.” ISRN Atmospheric Sciences 2013 (2013): 1–27. https://doi.org/10.1155/2013/786290.

[2] Lelieveld, Jos, Sergey Gromov, Andrea Pozzer, and Domenico Taraborrelli. “Global Tropospheric Hydroxyl Distribution, Budget and Reactivity.” Atmospheric Chemistry and Physics 16, no. 19 (2016): 12477–93. https://doi.org/10.5194/acp-16-12477-2016.

[3] Vilà-Guerau de Arellano, J., X. Wang, X. Pedruzo-Bagazgoitia, M. Sikma, A. Agustí-Panareda, S. Boussetta, G. Balsamo, et al. “Interactions Between the Amazonian Rainforest and Cumuli Clouds: A Large-Eddy Simulation, High-Resolution ECMWF, and Observational Intercomparison Study.” Journal of Advances in Modeling Earth Systems 12, no. 7 (2020): 1–33. https://doi.org/10.1029/2019MS001828.

How to cite: Ringsdorf, A., Edtbauer, A., Vila-Guerau de Arellano, J., Williams, J., and Lelieveld, J.: Determination of OH radical concentrations between 80-325 m over the Amazon rainforest using BVOC measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3731, https://doi.org/10.5194/egusphere-egu22-3731, 2022.

17:14–17:21
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EGU22-8810
Luiz A. T. Machado et al.

This study combines ground-based gas phase, particle, and rainfall measurements at the ATTO site to study the impact of rainfall events on greenhouse and reactive gas concentrations and discuss how this process is relevant for producing new particles. Measurements of CO2, CH4, CO, O3, NO, and NO2 concentrations were collected from the surface to 79m using a tower at the ATTO site in the central Amazon forest northeast of Manaus, Brazil. Particle size distribution was measured by an SMPS and rainfall by a rain gauge at the top of the tower. Data collection started in 2012, and this analysis covered the period up to 2020. The 30-minute interval dataset was used to study how convective events modify the concentration of these gases. During the rainfall events, CO2, CO, and CH4 concentrations decrease, though CH4 varies less with height than CO and CO2. The daily cycle of NO2 presents an interesting characteristic showing distinct daily evolution for the concentration in the upper and lower levels. The decrease in NO2 concentration in the upper level and the increase near the surface in the afternoon, which is the typical time of rainfall events, indicate that a specific process occurs near the surface. With the joint analysis of gas-phase observations with ultrafine particles and rainfall data, it was possible to evaluate the interesting physical-chemical processes occurring during the rainfall events that might be important for particles nucleation. The time of rainfall events was defined as the first-time rain rate reaching 3 mm/hours, a typical value of the beginning of convective rainfall events. Interestingly, during rainfall events, there is a significant injection of O3 above and inside the canopy, and at this moment, its concentrations can increase by 300%. At the same time, NO decreases, and NO2 increases its concentration, suggesting a reaction between NO and O3 forming NO2. The concentration of NO2 follows the increase in particle concentration smaller than 20nm. This result opens new perspectives on the role of new particle formation related to rain and vertical mixing in the Amazon.

How to cite: Machado, L. A. T., Pöhlker, C., Harder, H., Andreae, M. O., Artaxo, P., Botia, S., Cheng, Y., Franco, M. A., Kremper, L., Komiya, S., Lavric, J., Leliveld, J., Hang, S., Quesada, C. A., Pöhlker, M., Trumbore, S., Walter, D., Williams, J., Wolff, S., and Pöschl, U.: Amazonas Rainfall Modifying Gas Concentration and Forming Nucleation Particles Near the Surface, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8810, https://doi.org/10.5194/egusphere-egu22-8810, 2022.

17:21–17:28
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EGU22-11693
Hella van Asperen et al.

Methane (CH4) is one of the most important anthropogenic greenhouse gases. Despite its importance, natural sources of methane, such as tropical wetlands and termites, are still not well understood and a large source of uncertainty in the tropical CH4 budget. The Amazon rainforest is a key region for the (global) CH4 budget but, due to its remote location, local CH4 concentration and flux measurements are still rare.

Fieldsite ZF2 (60 km NW of Manaus, Brazil) is located in pristine tropical rain forest. At this fieldsite, a Spectronus FTIR-analyzer (measuring CO2, CO, CH4, N2O & δ13CO2) was installed at the foot of the K34 tower, set up to measure different heights above and below the canopy continuously. In addition, by use of a Los Gatos portable analyzer (measuring CO2 & CH4), additional semi-continuous concentration measurements were performed at the valley tower (studying the nighttime build up of valley CH4), above the igarapé  (capturing the CH4 ebullition bubbles leaving the water surface), and on the plateau (studying the spatial horizontal heterogeneity of CH4 concentrations within the canopy). Furthermore, the portable analyzer was used for soil, water, termite mound, and termites flux measurements.

By combining tower and flux chamber measurements, the role and magnitude of different ecosystem sources could be assessed. We observed that, while soils in the valley are a small source of CH4 (0.1 to 0.2 nmol CH4 m-2 s-1), overall the soils of this ecosystem are expected to be a net CH4 sink (-0.3 to -0.5 nmol m-2 s-1 ). Estimated total ecosystem CH4 flux, based on nighttime concentration analyses of the tower data, indicate that the ecosystem is a net CH4 source (~1 to 2 nmol CH4 m-2 s-1). We propose that the net CH4 emission of the ecosystem is driven by local emitting hotspots, such as the valley stream and standing water, termites and termite mounds (~1 nmol CH4 m-2 s-1), anoxic soil spots and decaying dead wood.

 

How to cite: van Asperen, H., Warneke, T., De Araújo, A., Forsberg, B., Ferreira, S., Alves-Oliveira, J., Ramos de Oliveira, L., de Lima Xavier, T., Sá, M., Teixeira, P., Pires, E., Moura, V., Komiya, S., Botia, S., Jones, S., Lavrič, J., Trumbore, S., and Notholt, J.: Tropical forest CH4 budget: the importance of local hotspots, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11693, https://doi.org/10.5194/egusphere-egu22-11693, 2022.

17:28–17:35
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EGU22-13294
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ECS
Pâmella Assis et al.

Soils of tropical forests generally have low fertility, therefore nutrient cycling has great importance in these ecosystem functions, once these soil elements are essential for vegetative tissue and plant metabolic processes. Understanding and quantifying the processes that involve nutrient acquisition, storage, and output in plants, and their relationship with forest productivity and biomass, is essential to characterize the ecosystem nutrient dynamics and understand how global environmental changes, such as the increase in CO2 can affect forest processes. Therefore, we investigated the nutrient dynamics of a terra firme forest in Central Amazonia, near Manaus, Brazil through the quantification of stocks, flows, and nutrient use efficiency in different compartments to estimate forest nutritional balance. We quantified the biomass stocks in the forest compartments – fine root, leaves, litterfall and stems – and their macro (N, P, Ca, Mg e K) and micronutrients (Fe, Mn e Zn) content. We estimated the nutrient fluxes through productivity rates, the nutrient stocks, and the nutrient efficiency, the inverse of nutrients concentration. Most of this information was available from the AmazonFACE (Free-Air CO2 Enrichment) baseline data. The study area has 8 permanent plots monitored since 2015 with periodic field collections and monitoring. We hypothesized that the macronutrient that cycles more efficiently in the ecosystem will potentially be the most limiting element to forest net primary productivity, adding to a better understanding of nutrient allocation and cycling, and greater accuracy in predictions from global vegetation dynamics models. The total forest biomass (above and belowground) in our study site was 200.85±0.52 Mg C ha-1 and the productivity 9.79±0.22 Mg C ha year-1. These results are higher than previous studies reported in the amazon forest. Ecosystem nutrient flow was greater in leaves > litter standing crop > fine roots > stems. On the other hand, ecosystem nutrient stocks were greater in stems > leaves > fine root > litter standing crop.  Our preliminary results show that phosphorus stock and flow are lower than other macronutrients, being, therefore, cycled more efficiently than other elements studied here. This suggests that phosphorus is potentially the macronutrient that most limits net primary productivity. For nitrogen, we observe a low-efficiency use, which was expected since this element is abundant in Central Amazon soils;  for potassium an intermediate efficient use, so the order of stocks and flows is N > K > P. For micronutrients nutrient efficiency use was as follows: zinc > magnesium > iron. These results suggest that phosphorus could be considered the most limiting macro nutrient to forest net primary productivity while zinc availability could also play a role. Our estimates of nutrient stocks and flows for a Central Amazon forest would improve our understand different nutrient dynamics and demands that impact biogeochemical cycles and functioning of these forests.

How to cite: Assis, P., Lugli, L. F., Aleixo, I., R. Bachega, L., Garcia, S., Santana, F., and Quesada, C. A.: Ecosystem nutrient budget in a Central Amazon forest: the role of nutrient stocks and flows in biogeochemical cycling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13294, https://doi.org/10.5194/egusphere-egu22-13294, 2022.

17:35–17:42
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EGU22-13341
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ECS
Pedro Ivo Lembo Silveira de Assis et al.

Leaf phenology impacts carbon, nutrient, and hydrological cycles from local to global scales. In central Amazon rainforest, the timing of leaf flush and abscission promotes a seasonal change in leaf age composition of the upper canopy. It has been singled out as the most important driver of photosynthetic capacity (PC) seasonality. However, limitations concerning on two important issues must be raised: 1) canopy leaf age temporal variation has not been directly assessed and 2) this approach has an empirical assumption that canopy leaf area should be fully replaced after 12 months. The first issue implies PC to be obtained by flux-towers measurements to estimate leaf age composition of the upper canopy. So, it is not a reliable representation of age distribution of the upper canopy. The concerning about the second issue relies on that tropical rainforest trees are known to present different leaf phenological patterns (e.g. deciduousness and evergreenness) which are correlated to leaf lifespan (LL), like for a year or more. Besides, leaves presenting higher LL show differences on PC compared to those of short ones, both in their maximum PC and its decay rate while aging. That means if leaves from plants with different leaf phenological pattern have the same age (e.g. in months), they will differ on their PC. Therefore, there is a necessity to elucidate leaf phenological patterns and unravel temporal changes on leaf age composition of upper canopy and LL variability. From August 2016 to November 2019 at the Amazon Tall Tower Observatory (ATTO), tagged leaves were censused monthly on ten upper canopy branches per tree (n = 36 trees). Temporal variation of storage, flush and abscission of leaves were recorded. Chronological ages were only possible for leaves flushing during the study period. Similarly, LL was obtained from leaves when both flush and abscission date were observed throughout the monitoring period. Around 80% of the trees flushed new leaves massively during the dry season. Eight of them (22%) fell into brevi-deciduous category while twenty-eight (78%) into evergreenness. Canopy leaf quantity proved to be nonseasonal as expected. On the other hand, seasonal change in leaf age composition of the upper canopy was confirmed. Still, it sheds light on its complex and diverse stratification. In the last month of monitoring, leaf age ranged from 0 to 43 months with only half of the leaves being younger than a year. Thus, leaf flush and leaf abscission present a seasonality. However, at least almost half of them have a lifetime longer than a year. This result suggests that half of the leaves from upper canopy are being neglected by the models. The LL presented a bimodal distribution (n = 2552 leaves) with two peaks around one year and two years, respectively. This suggest there are annual and biannual leaf phenological patterns between upper canopy trees. However, individual trees still show a bimodal distribution of LL frequency. This implies LL should not be used as a leaf functional trait to define plant functional groups.

How to cite: Lembo Silveira de Assis, P. I., Martins, G. A., Sanches, I., Nelson, B. W., Sá, M., Kesselmeier, J., and Manzi, A. O.: How does leaf phenology define upper canopy functional structure in a central Amazon upland forest? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13341, https://doi.org/10.5194/egusphere-egu22-13341, 2022.

17:42–17:45
Transition to the experiments in the Amazon

17:45–17:52
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EGU22-9067
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Highlight
Anja Rammig and David Lapola and the AmazonFACE team

The rapid rise in atmospheric CO2 concentration over the past century is unprecedented. It has unambiguously influenced Earth’s climate system and terrestrial ecosystems. Plant responses to rising atmospheric CO2 concentrations are thought to have induced an increase in biomass and thus, increased the carbon sink in forests worldwide. Rising CO2 directly stimulates photosynthesis (the so-called CO2-fertilization effect) and tends to reduce stomatal conductance, leading to enhanced water-use efficiency, which may provide an important buffering effect for plants during adverse climate conditions. For these reasons, current global climate simulations consistently predict that tropical forests will continue to sequester more carbon in aboveground biomass, while several lines of evidence point towards a decreasing carbon sink strength of the Amazon rainforest in the coming decades, potentially driven by nutrient limitation, droughts or other factors. Mechanistically modelling the effects of rising CO2 in the Amazon rainforest are hindered by a lack of direct observations from ecosystem scale CO2 experiments. To address these critical issues, we have been developing a free-air CO2 enrichment (FACE) experiment in an old-growth, highly diverse, tropical forest in the Brazilian Amazon and we present our main hypotheses that underpin the AmazonFACE experiment.  We focus on possible effects of rising CO2 on carbon uptake and allocation, phosphorus cycling, water-use and plant-herbivore interactions, and discuss relevant ecophysiological processes, which need to be implemented in dynamic vegetation models to estimate future changes of the Amazon carbon sink. We also report recent results from the open-top chamber experiments on understorey saplings under rising CO2 and phosphorus fertilization, recently conducted at the AmazonFACE site. We give an overview over phosphorus uptake strategies and potential modelling approaches.

How to cite: Rammig, A. and Lapola, D. and the AmazonFACE team: AmazonFACE – Assessing the response of Amazon rainforest functioning to rising atmospheric CO2 concentration, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9067, https://doi.org/10.5194/egusphere-egu22-9067, 2022.

17:52–17:59
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EGU22-2869
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ECS
Iokanam Pereira et al.

Tropical forests play a key role in the flux of terrestrial carbon (C). However, recent studies show tropical forest are losing over the years the ability to sink C from the atmosphere, one of the best explanations for that is the climate change caused by humanity in the last centuries and accelerating slightly every year. One of the ways to understand the changes in C fluxes in forest ecosystems in the short, medium, and long term are the Earth system models (ESMs). Nevertheless, simulations demonstrate that ESMs are not able to represent the decline in C sink by tropical forests in recent decades. Experiments that fertilize the atmosphere with carbon dioxide (eCO2) are essential to reduce uncertainties in future ESM projections about the possible effects of eCO2 on the carbon cycle. Open top chamber (OTC) allow the exposure of understory vegetation to eCO2 allowing the control and monitoring of the microenvironment in which they are inserted. Here, we describe the OTC system currently operating in the Amazon Free-Air CO2 Enrichment research program (AmazonFACE) in a mature forest in Central Amazonia, the analysis period is from 01/01/2020 to 12/31/2020. Each OTC is 2.40 m in diameter by 3.00 m in height, in which the concentration of CO2 ([CO2]) is monitored minute-by-minute using infrared gas analyzers, allowing the spatial and temporal control of [CO2]. The operation consists of keeping the [CO2] in the treatment OTCs (i.e., with eCO2) ≈ 200 µmol. mol1 above the [CO2] of the control OTCs (i.e., without eCO2) in the daytime (between 6:00 am - 6:00 pm). The [CO2] measurements on the treatment and control OTCs show that the desired concentration was successfully delivered, +262.4 ± 25.5 µmol / mol (mean ± SD) of the desired setpoint, i.e., 31 % above setpoint target. The eCO2 in the treatment OTCs worked 91% of the analyzed operational time, the remaining time was wasted with engineering failures (3%) and problems with the supply of CO2 (6%). The system was able to maintain the [CO2] above the setpoint, showing that the system configuration is capable of exposing understory vegetation even in a highly complex environment. The results demonstrate that the in-situ OTC system presented can be reproduced in different types of ecosystems, allowing better knowledge about metabolic processes that occur between atmosphere-plant-soil.

How to cite: Pereira, I., Takeshi, B., Guedes, A., Souza, C., Quesada, C., and Lapola, D.: An open-top chamber system for exposing Amazon understory vegetation to elevated atmospheric CO2, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2869, https://doi.org/10.5194/egusphere-egu22-2869, 2022.

17:59–18:06
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EGU22-8975
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ECS
Gabriela U. Neves et al.

The increase in atmospheric CO2 concentration positively affects plant carbon assimilation and carbon stock in different biomes. However, there are uncertainties regarding how plants in tropical forests, especially in the Amazon rainforest, will respond to this increase, since a large part of the soils in the region present natural low phosphorus (P) availability, which could constrain positive effects of elevated CO2. Here, we investigated if P addition would interfere on leaf primary carbon metabolism and aboveground development responses under elevated CO2. For that, we used 46  seedlings of Inga edulis Mart., a native leguminous nitrogen-fixing species, exposed for 10 months (November 2019 - September 2020) to CO2 and P treatments. Plants grew in pots - half with natural P availability (-P) and half with P addition (+P) -, inside CO2 enrichment chambers - half with ambient CO2 (aCO2) and half with elevated CO2 (aCO2 + 200 ppm; eCO2), - in the understory of a primary forest in Central Amazonia, Manaus, Brazil.  A factorial experimental design was used, with 11-12 plants for each treatment: aCO2-P (control), aCO2+P, eCO2-P and eCO2+P. To assess the carbon metabolism, we measured light-saturated net CO2 assimilation (Asat), leaf respiration in the light (Rlight), leaf respiration in the dark (Rdark) and photorespiration (PR). To assess aboveground development, we measured plant height and diameter, crown height and diameter,  number of leaves and total leaf area. We found that eCO2, regardless of P availability, significantly increased Asat and Rlight, while decreasing Rdark and Asat:Rdark ratio, but it did not affect PR . Those results suggest that seedlings indeed assimilated more carbon under eCO2. However, irrespective of CO2 treatment, +P significantly increased aboveground responses. Under P addition, plants showed greater height and greater crown development (higher crown height and diameter and larger leaves) compared to control or eCO2-only. Plant diameter and number of leaves did not respond to any treatment. We did not find differences between +P seedlings under different CO2 treatments (aCO2+P and eCO2+P), indicating that only P had an effect on these responses. Still, there were substantial changes on some of the aboveground responses between these treatments, particularly in total leaf area which increased 60% (aCO2+P) and 126% (eCO2+P) compared to control. Overall, we observed a distinguished pattern, in which eCO2 mainly affected physiological responses, while P addition consistently affected aboveground development. The lack of response of aboveground components under eCO2 suggests that the extra carbon assimilated was not necessarily used to aboveground development as shown by many studies. Our findings indicate that, in the short-term, eCO2 is highly important in determining changes in plant metabolism whereas it has little impact on growth, even when nutrient limitation is alleviate. However there is still need to understand if such responses will persist in the long-term and in other species, as these processes are key factors in determining forest responses to climate change.  

How to cite: U. Neves, G., R. Ferrer, V., Garcia, S., F. de Souza, V., Domingues, T., Aleixo, I., Tozzi, H., A. C. L. Pequeno, P., P. Martins, N., Guedes, A., S. Pereira, I., C. G. Menezes, J., R. M. Damasceno, A., R. Santos, Y., N. Garcia, M., C. M. Moraes, A., M. Pereira, A. C., Kruijt, B., and A. N. Quesada, C. and the AmazonFACE Team: Short-term responses of Inga edulis Mart. seedlings growing under elevated CO2 and phosphorus addition: understanding potential phosphorus constraints on plant responses to elevated CO2 in the understory of a central Amazon forest     , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8975, https://doi.org/10.5194/egusphere-egu22-8975, 2022.

18:06–18:13
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EGU22-2703
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ECS
Laynara F. Lugli and Carlos Alberto Quesada and the AmazonFACE team

One of the most important questions that remain open in terrestrial ecology refers to how the Amazon rainforest, the largest tropical forest in the world, will respond to elevated atmospheric CO2. Since a large part of the Amazon grows in soils with very low phosphorus (P) availability, understanding how potential nutrient limitation could impact forests in a changing world becomes crucial. There is strong evidence for a positive effect of elevated CO2 on plant growth but sustaining such a response in the Amazon would require plants to increase their access to P, making it important to understand the effects of elevated CO2 on root P-uptake strategies. To this end, we installed eight Open Top Chambers (OTC) in an understory forest in Central Amazon in Manaus, Brazil, being four control with ambient CO2 (aCO2) and four treatment with +200 ppm CO2 (eCO2). Inga edulis, a common N-fixing tree in the area, was chosen as study species. In each OTC, I. edulis was grown in six pots, three containing control soil from the study area and three containing control soil with 600 mg/kg of P added as triple super phosphate. After two years, plants were harvested and total soil respiration, total root dry mass, root nodulation, root morphological traits (mean diameter, specific root length – SRL, specific root area – SRA and root tissue density – RTD) and potential root phosphatase activity were measured. Total soil respiration was significantly higher in both treatments with eCO2 when compared to treatments with aCO2. Total dry root biomass followed a similar pattern, and root biomass in the eCO2 and P+eCO2 treatments were twice that of the other two aCO2 treatments. Plants invested in more fine roots (< 1 mm diameter) than in coarse roots with eCO2-only, whilst in P+eCO2, both fine and coarse roots biomass increased. No nodules were detected in control plants, whilst almost 75% of plants growing in P+eCO2 and 30% of plants growing in eCO2-only and P-only displayed nodulation. Mean fine root diameter for plants growing in eCO2-only was significantly higher than all other treatments, leading to a significant decrease in SRL and RTD, with no changes in SRA. In both treatments with eCO2, fine root phosphatase activity (expressed per root dry mass and specific area) significantly decreased in comparison to aCO2. However, when extrapolating root phosphatase activity for total fine root biomass, pot-level phosphatase exudation was twice as high in eCO2 than in aCO2 treatments. Our results clearly point to a shift in plant belowground strategies, suggesting an even stronger control of nutrient acquisition mechanisms by eCO2 than P addition. With eCO2, plants allocated much more biomass to fine roots and nodules, rather than increased phosphatase exudation per root-unit. Such trade-off suggests that in this scenario, plants might acquire P directly by exploring higher soil volumes, whilst allocating extra C to N-fixing bacteria. We demonstrate how eCO2 and P availability can shape belowground plant traits pointing to important trade-offs that could determine ecosystem-scale changes in future climate scenarios.

How to cite: F. Lugli, L. and Quesada, C. A. and the AmazonFACE team: The effects of elevated CO2 and phosphorus limitation shaping fine root functioning in Central Amazon forests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2703, https://doi.org/10.5194/egusphere-egu22-2703, 2022.

18:13–18:20
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EGU22-10939
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ECS
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Highlight
Bárbara Brum et al.

The Amazon covers an extensive area of tropical rainforest that directly affects global water and Carbon cycles. The biomass stored in this forest is a result of the dynamic balance between rates of mass gain due to productivity, and losses due to respiration and mortality. In general, these forests concentrate about 70-80% of biomass in the aboveground part, and the regional variation of AGB (aboveground biomass) can be explained by the compositional, structural, climatic and by differences in soil propriety and fertility between East-West gradient in the Amazon basin. This gradient drives a large set of variations in tree growth and mortality, resulting in differences on the forest structure and dynamics. In this context, direct manipulation of nutrients in soils is a powerful tool to investigate which elements limit tree growth and forest productivity. While nitrogen (N) is accumulated along soil development and age, the availability of rock-derived phosphorus (P) and cations may limit the ecosystems' functioning, including the potential increase in the productivity in response to elevation on CO2 concentrations in the atmosphere. To understand these patterns, a long-term, large-scale soil fertilization experiment in Amazonian forests (AFEX) was implemented in the Central Amazon. In 2017, 32 permanent plots were installed in areas of old-growth continuous forest belonging to the Biological Dynamics of Forest Fragments Project (PDBFF), in a full factorial design, with four blocks chosen at random, where 8 plots (each with a size of 50x50 m) were installed with different fertilization treatments for each block. The treatments are: P, N, cations, Control (no fertilization), N+P, N+cations, P+cations and N+P+cations. To estimate the effects of soil fertilization on AGB, we calculated the difference between biomass before and after four years of fertilization (2017 to 2021), using allometric equations performed data from diameter about 5,000 individuals (DAB ≥ 10 cm) measured annually and wood density. We analyzed the data with two different approaches, at the community and at genus level, considering three most abundant genera: Eschweilera, Pouteria and Protium. At community level, our results showed only non-significant trends between AGB in plots where N, P and cations were added. At genus level, we observed that Eschweilera and Protium had a negative relationship to N and Pouteria had a positive trend.  Conversely, only Protium increased AGB with P addition.  Pouteria and Protium was negatively affected by cations, while Eschweilera showed no response. These results indicate that, although overall positive or negative trends in biomass increment appear at the community level, the highly diverse forest studied does not have a homogeneous response to nutrient addition, and that each taxonomic group could potentially be limited by different nutrients. In the long term, we expect that these patterns may change the forest structure, dynamics and composition and, consequently, the stocks of biomass, impacting the functionality of these forests. These results improve our understanding of the role of nutrients affecting forest biomass, and may reduce uncertainties in vegetation dynamics models and predictions on environmental changes.

How to cite: Brum, B., Quesada, C. A., Assis, R., Schietti, J., Aleixo, I., di Ponzio, R., Hartley, I., Andersen, K., Cunha, H. F., Lugli, L., Martins, N., Almeida, R., Pires, M., Pinheiro, N., Moraes, A. C., Camargo, J. L., Ribeiro, G., Takeshi, B., Siebert, L., and Andrade, F.: Effects of soil fertilization on aboveground biomass in an old-growth forest in Central Amazon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10939, https://doi.org/10.5194/egusphere-egu22-10939, 2022.

18:20–18:25
Final remarks and future steps