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 manipulative 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 and nutrient dynamics, ecosystem microbial activity, nutrient cycling or plant-soil interactions.
Orals: Wed, 6 May, 08:30–12:30 | Room N1
High-latitude ecosystems play a central role in the global carbon cycle, yet their responses to climate warming remain one of the largest sources of uncertainty in Earth system projections. Most models assume that warming accelerates nitrogen (N) cycling, alleviates plant N limitation, and enhances vegetation productivity, thereby buffering warming-induced soil carbon (C) losses. This paradigm implies that nutrient feedbacks stabilize ecosystem C storage under rising temperatures. However, growing experimental evidence challenges this assumption.
In this talk, I synthesize results from long-term soil warming studies along natural geothermal gradients in subarctic ecosystems to reassess how warming reshapes C–N coupling, nutrient retention, and ecosystem resilience. Across years to decades of sustained warming, we observe large and proportional losses of soil C and N, despite increased microbial activity and N mineralization. Crucially, enhanced N availability does not translate into sustained plant growth or long-term ecosystem C gains.
Our findings reveal a mechanistic shift in ecosystem functioning under warming: increased microbial metabolic costs and carbon limitation reduce microbial biomass and weaken key nitrogen stabilization pathways. Microbial and fine-root N pools, critical short- and long-term N reservoirs in cold ecosystems, decline with warming, particularly during winter and snowmelt periods when plant uptake is low. Seasonal increases in plant N uptake during the growing season are too small and too transient to compensate for these losses. This leads to an effective “opening” of the N cycle, increased N losses, and stoichiometrically coupled soil C losses.
Although microbial communities eventually reorganize toward more conservative N cycling under long-term warming, this physiological adjustment stabilizes fluxes rather than restoring depleted soil C and N stocks. As a result, early warming-induced losses may be effectively irreversible, even under later ecosystem acclimation.
Taken together, these results suggest a fundamental conceptual shift: warming does not simply accelerate biogeochemical cycles but erodes the mechanisms that retain nutrients and carbon in high-latitude soils. This challenges the widespread assumption that nitrogen feedbacks buffer carbon losses and highlights the need to explicitly represent microbial physiology, nutrient retention, and seasonal asynchronies in Earth system models to improve predictions of carbon–climate feedbacks.
How to cite: Marañon, S.: When Nitrogen Retention Fails: Carbon Losses in a Warming Arctic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7186, https://doi.org/10.5194/egusphere-egu26-7186, 2026.
The West Antarctic Peninsula is among the fastest-warming regions on Earth and may be approaching a climatic tipping point [1,2]. Ongoing warming threatens the stability of frozen ground and permafrost, with potentially important consequences for terrestrial carbon and nutrient cycling. In Antarctic terrestrial ecosystems soil microorganisms represent the dominant biological drivers of biogeochemical processes. However, their role in regulating carbon turnover and greenhouse gas production during summer thaw remains poorly constrained. Here, we present observations from eight terrestrial sites along the West Antarctic Peninsula, where the last seven years have been the warmest on record [2]. Soil surface temperatures ranged from 2.3 to 17.1 °C (mean 8.5 °C). We combined shotgun metagenomics with soil geochemistry, geological context, and interstitial soil gas composition and isotopic fingerprint to characterize microbial taxonomic and functional diversity and its environmental controls. Microbial community composition and metabolic potential differed markedly among sites and showed a strong relationship with soil temperature. Metagenomic data reveal widespread genetic potential for the degradation of complex and refractory organic matter, indicating that Antarctic soil microbial communities actively contribute to carbon mobilization and greenhouse gas production under sustained warming. By integrating microbial, geochemical, and geological observations, this study provides new process-level insights into terrestrial ecosystem responses to climate change in polar regions. Our results offer empirical constraints on microbial-driven soil carbon dynamics that are currently underrepresented in ecosystem and Earth system models, highlighting the need to explicitly account for Antarctic soil microbial processes when predicting future biogeochemical cycling in a warming climate.
- Masson-Delmotte, V. et al. (eds) IPCC (Cambridge University Press, 2021).
- Gorodetskaya, I.V., Durán-Alarcón, C., González-Herrero, S. et al. npj Climate and Atmospheric Science 6, 202 (2023).
How to cite: Brusca, J., Gallo, G., Bradley, J., and Giovannelli, D.: Microbial controls on soil carbon mobilization under global warming along the West Antarctic Peninsula, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7608, https://doi.org/10.5194/egusphere-egu26-7608, 2026.
Soil respiration (Rs) is the largest terrestrial flux of carbon dioxide (CO2) to the atmosphere, with tropical forests contributing disproportionately to global Rs. Rising temperatures associated with climate change are expected to substantially alter tropical soil carbon (C) cycling by stimulating microbial activity and accelerating organic matter decomposition and influencing plant and root respiration. However, the extent to which warming alters the relative contributions of autotrophic (Ra) and heterotrophic (Rh) respiration remains poorly constrained. Distinguishing these sources is necessary to understand the mechanisms underlying their responses. Radiocarbon (14C) analyses provide a powerful approach for resolving respiration sources and assessing the age of respired C. Here, we used 14C measurements to examine how experimental warming alters source contributions at the Tropical Responses to Altered Climate Experiment (TRACE) in Puerto Rico, where infrared heaters increase understory and surface soil temperatures by 4°C above ambient conditions. Surface soil gas samples were collected for 14C analysis of Rs, soil incubations were used to constrain the Rh end-member, and atmospheric samples represented the Rₐ end-member. All gas samples were purified for CO2, graphitized, and analyzed by accelerator mass spectrometry. Soil respiration in control plots exhibited a modern radiocarbon signature, whereas warmed plots showed significantly higher Δ14C values, indicating increased contributions from decades-old C (“bomb C”). The Rₕ end-member also became significantly older under warming. Isotope mixing models revealed a pronounced shift in source contributions, with Ra decreasing and Rh approximately doubling under warming. These results indicate that increased temperatures enhanced microbial decomposition of older soil C, altering the balance between autotrophic and heterotrophic respiration. Such warming-induced shifts in respiration sources are not detectable from measurements of total CO2 fluxes alone and highlight the importance of source partitioning for assessing the vulnerability of tropical soil C under sustained warming. These findings also provide critical constraints for improving Earth system model representations of tropical soil C-climate feedbacks.
How to cite: Cruz-Pérez, R., Barreto-Vélez, T., Ortiz-Iglesias, D. A., Rubio-Lebrón, L. C., McFarlane, K., Cavaleri, M., Reed, S., Wood, T. E., and Kaye, J.: Effect of experimental warming on sources of soil respiration in a tropical forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23021, https://doi.org/10.5194/egusphere-egu26-23021, 2026.
Ecosystem respiration (ER) is the largest source of biogenic CO₂ to the atmosphere, and its temperature sensitivity (Q₁₀) is key to land–climate feedback. However, despite decades of studies finding that Q₁₀ varies considerably across space, time, and biomes, the drivers controlling this variation remain unclear. Here we show that Q10 variability of can be unified within a common hydrothermal framework. Using data from 142 eddy covariance sites around the world, we reveal that Q₁₀ exhibits unimodal responses to soil moisture. At each site, Q₁₀ first increases with soil moisture, peaks at a threshold (SMₜₕ), and then declines. This SMth is ecosystem-specific, which emerges from coordinated plant–soil–microbial interactions, shaped by long-term hydroclimatic regimes and soil physical constraints. Global mapping of SMₜₕ shows that about 25% of the planet’s vegetated land currently has a soil moisture level that exceeds SMₜₕ, including many carbon-rich peatlands and tropical forests, where moderate drying could enhance temperature sensitivity and carbon loss. Our findings establish that moisture thresholds offer an ecological framework that unifies the regulation of carbon fluxes through water and heat. Incorporating this framework into Earth system models will fundamentally improve predictions of carbon–climate feedback under accelerating hydroclimatic change.
How to cite: Zhang, Q., Wang, S., Zheng, Q., Wang, J., Yi, C., and Niu, S.: Soil moisture thresholds for the temperature sensitivity of ecosystem respiration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4617, https://doi.org/10.5194/egusphere-egu26-4617, 2026.
The AmazonFACE experiment is a large-scale Free-Air CO₂ Enrichment (FACE) experiment designed to assess the responses of Amazonian tropical rainforests to elevated atmospheric carbon dioxide concentrations. As the world’s first FACE experiment in a mature tropical forest, AmazonFACE addresses a critical gap in our understanding of how these ecosystems will function under future climate conditions. The primary objective is to quantify the impacts of elevated atmospheric CO₂ concentration on forest carbon cycling, productivity, nutrient dynamics, biodiversity, and ecosystem resilience. The experiment is currently in the construction phase, with infrastructure installation, site preparation, and system testing actively underway. In parallel, extensive baseline measurements of atmospheric, ecological, and biogeochemical variables are being conducted to characterize pre-treatment conditions. Recent years have seen a growing body of scientific publications, technical reports, and outreach materials that document the experimental design, methodological challenges, and expected research outcomes, and the importance of AmazonFACE for policy making. These contributions highlight the complexity of operating FACE technology in remote tropical environments and the innovative solutions being developed. Once operational, AmazonFACE will enable the assessment of ecosystem responses to elevated CO2 under realistic field conditions. The data generated are expected to substantially improve Earth system models and projections of the global carbon cycle. Overall, AmazonFACE represents a major international research effort with far-reaching implications for climate change science and tropical forest management.
How to cite: Rammig, A., Lapola, D., and Betts, R. and the AmazonFACE Team: AmazonFACE: Current status and scientific objectives of the large-scale Free Air CO2 Enrichment Experiment in the Amazon rainforest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13940, https://doi.org/10.5194/egusphere-egu26-13940, 2026.
The impact of enhanced atmospheric CO2 (eCO2) concentrations on the Amazon forest's capacity to continue acting as a carbon (C) sink largely depends on soil nutrient availability. In particular, phosphorus (P) and the ability of plants to balance the extra CO2 with the additional nutrient demand play an important role in highly weathered tropical soils. We hypothesize that plants may allocate the extra C belowground to different nutrient acquisition mechanisms, thereby alleviating nutrient limitation. Potential changes in nutrient acquisition mechanisms include an increase in fine root productivity, adjustments in root morphological traits, and investment in arbuscular mycorrhizal fungi symbioses that will enhance nutrient foraging capacity. Additionally, the plant community could increase root labile C exudation, which can be utilized by the microbial community as an energy source, leading to increased extracellular enzyme production and enhanced nutrient mineralization. Furthermore, it is important to highlight the litter layer as a significant nutrient source, and root mats growing in the litter layer allow roots to intercept newly mineralized nutrients before they reach the soil.
Here, we increased atmospheric CO2 by ~300 ppm in situ, in a P-depleted Amazonian forest understory using open-top chambers, which not only increased plant C assimilation but also promoted aboveground biomass growth. Therefore, our primary goal was to better understand the mechanisms and adaptations at the root-soil interface that facilitated this positive CO2 fertilization response. Our results show that in the litter layer, eCO2 did not change net root productivity, but increased specific root length, indicating an enhanced foraging strategy. In contrast, in soil, eCO2 caused a decrease in root productivity, but an increase in arbuscular mycorrhizal fungi colonization, which may represent an alternative foraging strategy for plant communities. Simultaneously, eCO2 induced a significant decrease in the soil enzyme C and P stoichiometry, and a decline of the soil organic P fraction. One year later, a decrease in leaf litter P was observed under eCO2, which suggests that the adaptations of litter-based fine roots to eCO2 may have longer-term consequences for litter P recycling.
Taken together, our experiment provides in situ evidence that eCO2 promotes different root responses along the litter-soil continuum, which may alter P availability and intensify competition between plant roots and soil microorganisms. Such multiple spatial adaptations in root P acquisition strategies may strongly regulate plant-soil belowground dynamics and need to be considered to better understand the resilience of the Amazon forest to future climate change.
How to cite: P. Martins, N., Fuchslueger, L., F. Lugli, L., Rammig, A., P. Hartley, I., J. Norby, R., Hofhansl, F., and A. Quesada, C. and the AmazonFACE team: Amazon forest's carbon sink strength depends on plant nutrient efficiency at the root-soil interface, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12993, https://doi.org/10.5194/egusphere-egu26-12993, 2026.
Phosphorus (P) can restrict the capacity of forests to store additional carbon (C) with increasing carbon dioxide (CO2) concentration. Although P limitation is widespread, P addition experiments in mature forests are rare, leaving large uncertainties about whether alleviating P limitation under elevated CO2 (eCO2) will enhance C storage or instead shift limitation toward nitrogen (N). Here, we used a parallel P-fertilization x eCO2 manipulation in a mature forest to investigate the acute nutrient cycling response to P fertilization under eCO2 with a particular focus on N cycling. In April 2023, a mature P-limited Eucalyptus Forest at the Euc-Free Air CO2 Enrichment (Euc-FACE) experiment in Australia, was fertilized with 1.5 g P m-2 following 10 years of CO2 enrichment. We measured soil gross N mineralization and compound-specific depolymerization rates – offering novel insights into microbial metabolic pathways – alongside extracellular enzymatic activities, and nutrient pools in the top 10 cm of soil before P addition, 10 days and two months afterwards. We found that P addition decreased extracellular soil enzymatic activities associated with C-N-P-mining (─ 50%), increased microbial NH4+ retention (immobilization: mineralization ratio; + 23%) and microbial C use efficiency (CUE; + 12%), causing a reduction in plant-available N (─ 30%) independently from eCO2. Under eCO2, P addition stimulated protein depolymerization and C-P enzyme activities. Compound specific analyses revealed increased microbial biosynthesis with P addition via the assimilation of key amino acids such as alanine, glycine and glutamate. These findings indicate that P limitation constrains microbial C-N cycling under eCO2 by diverting microbial C investment toward P acquisition rather than growth. While alleviating P limitation can rapidly stimulate microbial cycling and promotes microbial C retention under eCO2, this response may only be transient, as enhanced microbial growth drives the system towards N limitation.
How to cite: Rumeau, M., Sgouridis, F., A. Macdonald, C., Pisetta Raupp, P., Warren, C., K. Reay, M., MacKenzie, A. R., Ullah, S., and Carrillo, Y.: Phosphorus limitation constrains microbial carbon–nitrogen cycling in a Eucalyptus forest under elevated CO2: evidence from EucFACE, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21587, https://doi.org/10.5194/egusphere-egu26-21587, 2026.
Temperate forests are a significant terrestrial carbon sink and can help mitigate rising CO2 concentrations in the atmosphere. Under elevated CO2 (eCO2) conditions, a higher rate of photosynthesis can drive forest biomass productivity; however, this response can be constrained by the availability of soil nutrients, namely nitrogen (N) and phosphorus (P). To alleviate these deficiencies, increased allocation of carbon (C) belowground could drive processes which can enhance nutrient uptake, thereby supporting the growth of mature forests under eCO2. However, the belowground processes and their interactions with above-ground disturbances (e.g. moth infestation) driving this change remain unclear. These belowground processes may involve fine root biomass growth, soil nutrient cycling, extracellular enzymatic activities, microbial biomass, and their interactions.
Here, we investigated whether eCO2 affects belowground processes and their interaction with disturbances (moth outbreak). The experiment was conducted at the Birmingham Institute for Forest Research Free Air Carbon Dioxide Enrichment (BIFoR FACE) facility, which comprises six experimental arrays surrounding woodland patches of c. 30 m diameter. Three of these arrays are enriched with eCO2 (+150 ppm above ambient), and three are under ambient CO2 levels. Within all six arrays, soil and root samples were collected from the top 0-30 cm covering O, A and B horizons. Fine root biomass stocks, soil N and P levels, root C, N and P content, microbial biomass C, N and P concentration, and extracellular enzymatic activities were quantified from 2017 to 2022.
We found that under eCO2, root biomass and microbial biomass were significantly greater, especially in the O soil horizons. No change in microbial biomass C: N: P stoichiometry was observed, but root P concentrations declined, and root C: N and C:P ratios increased under eCO2. In addition, while ammonium concentrations were significantly greater under eCO2, there was a trend towards lower phosphate and nitrate concentrations under eCO2. Potential C, N and P cycle enzyme activities increased under eCO2, and the LAP: AP ratio declined under eCO2. Overall, the changes observed under eCO2 suggest greater belowground C allocation under eCO2, and changes in nutrient cycling, which may have resulted in P becoming relatively less available than N. However, during the summers of 2018 and 2019, moth outbreaks caused widespread oak defoliation and reduced forest productivity substantially. The available data from this period suggests that soil nutrient availability increased substantially, likely as a result of leaf litter and frass inputs and low tree nutrient uptake following defoliation. Greater soil nutrient availability resulted in microbial biomass N pools and fine roots proliferation in the O soil horizon. These results may suggest that the insect outbreak had substantial impacts on tree responses to eCO2 over an extended time period, potentially controlling whether eCO2 productivity gains were allocated to long versus short-lived tissues.
How to cite: Akhtar, H., Hartley, I., Ullah, S., Hamilton, L., Mayoral, C., Grzesik, R., Mackenzie, R., Smith, A., Kourmouli, A., and Reay, M.: Interaction with elevated CO2 and disturbances on belowground processes in a mature temperate forest , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11363, https://doi.org/10.5194/egusphere-egu26-11363, 2026.
Rising reactive nitrogen (N) deposition and corresponding shifting phosphorus (P) availability can alter plant carbon (C) allocation belowground and modify soil fungal communities, with uncertain consequences for decomposition of soil organic matter (SOM) and hence C storage. Ectomycorrhizal (ECM) fungi are a major pathway for plant C to enter soils and can regulate SOM decomposition through opposing mechanisms, either stimulating free-living microbial activity (Priming effect) or suppressing decay via competition with saprotrophs (Gadgil effect). However, how N and P addition shifts the balance between these pathways remains unresolved, particularly in mature forests that are likely nutrient limited.
We investigated hyphal-mediated controls on decomposition under a factorial N and P addition experiment (control, +N, +P, +N+P) in a mature temperate oak forest, using nested in-growth bags containing either oak leaf litter (litter) or tongue depressor fragments (wood). Two outer mesh sizes manipulated hyphal ingrowth, with a 41-µm mesh allowing fungal entry and a 1-µm mesh largely excluding fungi and roots. Because ECM hyphae can forage over large areas and proliferate through nutrient-poor substrates, we expected this manipulation to mainly affect ECM contributions. Microbial respiration, C-based mass loss, hyphal biomass, potentials enzyme activities of peroxidase (PEROX) and phenol oxidase (PHENOX), and substrate-induced respiration were quantified, and fungal communities of wood were profiled by ITS1 amplicon sequencing.
The mesh treatments generated clear differences in hyphal biomass (p = 0.002) without altering bag moisture or pH (p > 0.05). By the second sampling, linear mixed models showed substrate- and nutrient- specific ECM effects on decomposition. For litter, fungal inclusion increased mass loss by 15.83% compared with exclusion bags (p = 0.012) and substrate-induced respiration by 31.82% (p = 0.019), whereas N enrichment decreased microbial respiration by 16.45% (p = 0.030). In contrast, fungal inclusion did not significantly affect wood mass loss (p = 0.562). Instead, N fertilisation reduced mass loss by 37.84% compared with controls (p = 0.048) and was associated with lower oxidative enzyme potentials (PHENOX: p = 0.085, PEROX: p = 0.15). Similarly, PERMANOVA analysis on fungal communities of wood reflect significant effects of nutrient addition (p = 0.002) and ANCOM-BC analysis shows that N addition significantly altered many fungal classes in wood.
These findings suggest that ECM controls on decomposition are substrate-dependent, and that nutrient supply can redirect fungal foraging and competition with saprotrophs. In mature forests, fertilisation may decouple carbon inputs to the mycorrhizal association from decay responses by reducing plant investment belowground and by reshaping fungal communities. This context dependence helps explain why fertilisation experiments often yield inconsistent soil carbon outcomes. Therefore, to improve projections of forest carbon cycling under rising N deposition and shifting P availability, mycorrhizal effects on decomposition should be linked with nutrient availability and substrate quality.
How to cite: Feng, X., Ullah, S., Hamilton, L., Mackenzie, R., Smith, A., Akhtar, H., Tennant, R., Mercado, L., and Hartley, I.: Ectomycorrhizal Decomposition Responses to Nutrient Addition in a Mature Temperate Deciduous Forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9993, https://doi.org/10.5194/egusphere-egu26-9993, 2026.
Global warming has extended the growing season in temperate forests, and this trend is expected to continue. While changes in forest physiological processes enhance our understanding of carbon uptake and phenology, the mechanisms underlying interannual variability in carbon balance across adjacent different forest types under similar monsoon-influenced climatic conditions, particularly in East Asia, remain unclear. This study aimed to identify the ecophysiological and phenological drivers of net carbon uptake based on eddy covariance flux observations from adjacent temperate forest ecosystems in East Asia, affiliated with the KoFlux and JapanFlux networks: evergreen forests and deciduous forests. The interannual variability of net ecosystem production (NEP) in evergreen needleleaf forests (ENF) was generally dominated by environmental controls, particularly water availability and temperature. In contrast, in deciduous forests—including both deciduous broadleaf and deciduous needleleaf forests (DBF and DNF)—interannual variability of NEP was largely regulated by environmental conditions but consistently modulated by phenology, with the timing and duration of carbon uptake playing an additional and critical role across East Asia. The results of this study are expected to have high applicability as a foundational dataset for future improvements in global carbon budget predictions driven by climate change. Not only do they provide scientific data to support future carbon neutral, but they also reveal the interannual variability characteristics of carbon uptake through the integrated consideration of ecophysiological and phenological factors.
How to cite: Hong, J., Lee, H., Kim, S., Lee, M., Park, J., Hirata, R., and Kim, H. S.: Similar Climate, Different Carbon Uptake: Ecophysiological and Phenological Controls on Interannual Variability in Nearby Evergreen and Deciduous Forests of East Asia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18159, https://doi.org/10.5194/egusphere-egu26-18159, 2026.
Boreal forests store approximately one-third of the global carbon (C) pool, and the C sink capacity of Fennoscandian boreal forests has increased steadily over the past century. However, recent evidence indicates a marked decline in C uptake during the last decade, with some areas transitioning to net C sources. The drivers of these changes are complex, involving interactions between forest management and climate change.
Fennoscandian forests have been intensively managed for centuries, with only small remnants remaining virgin. Since World War II, stand-based forestry dominated by clear-cutting and planting has become the prevailing practice, enhancing timber production and tree C uptake. Yet, its long-term effects on soil C dynamics, ecosystem functioning, and resilience remain poorly understood.
The EcoForest project investigates the long-term impacts of clear-cutting on biodiversity, carbon dynamics, and ecosystem functions in Norway spruce (Picea abies) forests along climatic gradients. We established paired plots of mature forests: one previously clear-cut (CC) and one near-natural (NN), matched for macroclimate, topography, and soil properties. CC stands had higher tree density, while NNs exhibited greater structural heterogeneity, light variability, and crown length. Deadwood volume was three times higher in NNs than in CCs.
We monitored tree litterfall continuously for two years and measured soil respiration monthly during one snow-free season. Ground vegetation litterfall was estimated via destructive sampling. CC stands exhibited 12% higher annual soil respiration, 20% greater tree litterfall, and a tendency toward higher total aboveground litterfall (12%), whereas NNs had 45% greater ground vegetation litterfall. Deadwood from CC stands showed higher respiration rates in laboratory assays, likely due to differences in wood properties that, in turn, led to different fungal decomposer communities. Overall, current net soil C balance appears similar between CC and NN stands.
Our findings demonstrate that management history exerts a lasting influence on key ecosystem processes, including litterfall composition, deadwood decomposition, and soil respiration—factors often overlooked in current carbon models that treat forests as homogeneous units. By integrating these dynamics, models can better capture variability in carbon fluxes across clear-cut and near-natural stands. The EcoForest project provides a unique natural experiment, offering critical insights for improving ecosystem models and enhancing predictions of boreal forest carbon balance under future climate and management scenarios.
How to cite: Nybakken, L., Madsen, R. L., Kjønaas, O. J., Kauserud, H., Birkemoe, T., Lunde, L. F., and Asplund, J.: Clear-Cutting and Carbon Balance in Boreal Forests: Evidence from a Natural Experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16065, https://doi.org/10.5194/egusphere-egu26-16065, 2026.
Pyrogenic carbon (PyC), the residues produced by the incomplete combustion of organic matter, is widely reported to play an important role in long term terrestrial carbon storing owing to its potential for millennial scale turnover when incorporated into soils.
The Amazon has been subjected to infrequent anthropogenic fires within the past 10,000 years, as well as more recurrent and higher impact wildfires within the modern period. These fires have contributed PyC to the soil carbon stocks at varying rates across the Amazon basin, as revealed by extensive soil sampling across a range of locations with varying meteorological, soil, vegetation and land use conditions.
This dataset, accompanied by radiocarbon dating, reveals key information about the fire regime of the amazon basin (e.g. fire recurrence). However, some key aspects of the fire and PyC patterns require further investigation to gain further understanding of the Amazon fire regime and its carbon cycling significance. Additionally, research into the carbon cycling significance of PyC in the Amazon is currently limited and requires further assessment, as well as the role it may play under future climate changes.
Here, the RothC soil carbon model is used to evaluate:
- The specific conditions required to produce the observed soil organic carbon and PyC stocks per site
- The carbon cycling significance of PyC in the Amazon and under projected climate scenarios
This study uses site specific data (e.g. soil clay levels and site meteorology) as well as a range of modelled fire/PyC scenarios to reconstruct past conditions and evaluate soil PyC up to 2100. The investigation points to Amazon basin PyC stocks in the range of 100-1000’s of megatonnes with a millennial scale turnover rate, indicating that this is a key carbon store that needs to be considered under future climate modelling for the Amazon.
How to cite: Kennedy-Blundell, O.: Simulating pyrogenic carbon in old growth Amazon forest sites with the RothC model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10310, https://doi.org/10.5194/egusphere-egu26-10310, 2026.
The AmazonFACE programme (Free-Air CO2 Enrichment) will subject areas of old-growth forest in the Amazon basin near Manaus to elevated (+200ppmv) CO2 concentrations to determine the effects on vegetation. While elevated CO2 is assumed to have significant fertilisation effects, both increasing productivity and reducing transpiration, this needs to be measured in the field. The fertilisation effects may not be as great as predicted due to limitations from the available nutrients, and soil in this part of the Amazon is known to be poor in phosphorus. The programme will be supported by modelling, including a version of JULES (the Joint UK Land Environment Simulator) called JULES-CNP which includes phosphorus dynamics and its interactions with the nitrogen and carbon cycles. Here this version has been especially set up to work in the forest near Manaus by using observation-based soil chemistry and weather data. JULES shows large increases in productivity (and in litter, soil carbon and respiration from the soil) with elevated CO2 without the phosphorus limitations, but significantly smaller increases in productivity when the phosphorus dynamics and interactions are included. The current JULES setup and configuration can be used with experimental investigation in AmazonFACE to inform future model improvements.
How to cite: Cook, P. A., Betts, R., Nakhavali, M. A., Goncalves De Souza, J., Kurganskiy, A., Mercado, L., and Duran-Rojas, M. C.: Modelling tropical forest responses to elevated CO2 in a nutrient-limited environment: JULES simulations at the AmazonFACE site, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10189, https://doi.org/10.5194/egusphere-egu26-10189, 2026.
The response of net forest carbon uptake to warm extremes remains elusive. The year 2023 was at the time “the hottest year on record” globally, with Canada’s forests experiencing warm anomalies of above 2 °C and unprecedented drought and wildfires, providing a unique case to examine the response of boreal forest net carbon uptake to climate extremes. Here we combine satellite-based atmospheric CO2 flux inversions, and ground in-situ observations of CO2 fluxes and concentrations to investigate Canada’s forest net carbon uptake and its underlying mechanisms in 2023. We find that compared to 2015–2022, the Canada’s forest net carbon uptake was enhanced by 0.28 ± 0.23 PgC, offsetting 38–48% of Canadian wildfire emissions in 2023. This enhanced net uptake was dominated by large ecosystem respiration reductions, mainly attributable to severe root-zone soil moisture deficits and the unimodal temperature response of respiration. However, most dynamic global vegetation models failed to simulate the respiration reductions and the responses to hydrothermal conditions well. This study improves our understanding of boreal forest net carbon uptake in response to climate extremes and highlights an urgent need to improve vegetation models under global warming.
How to cite: Dong, G. and Jiang, F.: Canadian net forest CO2 uptake enhanced by heat-drought via reduced respiration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1550, https://doi.org/10.5194/egusphere-egu26-1550, 2026.
Distributed experimental networks (DENs) provide unprecedented opportunities to quantify how ecosystem responses to global change across gradients. Process-based models have been previously used together with such manipulative experiments to identify knowledge gaps in models. However, experiments suffer from their own limitations in terms of what, and when, measurements can be taken. Models can offer a powerful tool to provide additional information and key insight into different stages of such experiments. Here we demonstrate that DENs and process-based models can serve a bi-directional diagnostic role: testing model fidelity while revealing where experimental design may systematically bias inference
We simulated ‘International Drought Experiment’ (IDE) drought treatments at grassland site lasting over two growing seasons using QUINCY, a land-surface model of coupled C-N-P cycling, and compared simulated aboveground net primary productivity (ANPP) responses with experimental observations. The model can reproduce the observed relationship between ANPP drought response and drought severity, with overlapping slope confidence intervals (experimental: 0.60 [0.30-0.90]; simulated: 0.79 [0.40-1.18]). Mean simulated ANPP reductions (36%) aligned with IDE synthesis estimates (21-38%), although site by site comparison shows a poorer fit.
Beyond this simple model-data comparison, we can use the model to explore aspects of ecosystem behaviour that cannot easily be measured. We performed model simulations over a range of drought intensities for each site and show that multiple sites exhibited a threshold behaviour – abrupt productivity declines over narrow exclusion ranges. Second, 63% of simulated sites displayed growing season shifts (≥1 month) during drought, with 29% in the first year. The interplay between these two mechanisms – threshold like responses and phenological shifts – produced a critical effect: depending on harvest timing, the magnitude and in some cases the sign of apparent ANPP changes varied substantially.
On the basic model evaluation side, site-level mismatches reflect potential structural constraints in the model (coarse plant functional types, absent competition dynamics producing threshold-like responses). Critically, and in addition to simple model evaluation, the widespread prevalence of growing-season shifts (63% of sites) demonstrates that point sampling could systematically bias inference even in well-designed, standardized experiments – a constraint that cannot be detected from the experimental data alone. This demonstrates that models can enhance the information from manipulative experiments and could either be used post-hoc, as in our study, to add insights to experimental data or prior to experiments to guide design and sampling regimes.
How to cite: Daly, L., Caldararu, S., Audrey Abadie, C., Smith, M., and Ohlert, T.: Using process-based models to enhance observations from distributed drought experiments., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9954, https://doi.org/10.5194/egusphere-egu26-9954, 2026.
Tree mortality is increasing globally due to climate extremes, disturbances, and biotic stressors, with profound consequences for ecosystem carbon cycling. However, the extent to which spatial patterns and temporal dynamics of tree mortality influence the functioning of ecosystems as a whole remains poorly quantified.
In this study, we investigate how tree mortality impacts key ecosystem functional properties, focusing on light-saturated gross primary productivity (GPPsat) and maximum net ecosystem production (NEPmax). Ecosystem functional properties were derived from long-term, half-hourly eddy covariance measurements across a range of forest ecosystems. Spatially explicit information on forest cover and tree mortality was obtained from satellite-based predictions of the deadtrees.earth initiative, which integrates drone-based observations with Earth observation data to produce multitemporal mortality and forest cover estimates at global scale.
We assessed whether including tree mortality information in addition to environmental drives improves the explanation and prediction of global and site-level variability in the flux-derived ecosystem functional properties; GPPsat and NEPmax. Model performance and variable importance patterns were compared between scenarios with and without forest cover and mortality dynamics to quantify the added explanatory power.
This study aims to provide the first systematic assessment of how spatially explicit tree mortality information contributes to ecosystem functional properties derived from eddy covariance data, and to evaluate whether integrating tree mortality observations can improve our understanding of the controls of ecosystem productivity and carbon balance under ongoing climate change.
How to cite: Katal, N., Mosig, C., Mahecha, M. D., Lusk, D., Jehle, J. V., Neumeier, P., Pfenning, M., Migliavacca, M., Musavi, T., Nelson, J. A., and Kattenborn, T.: Assessing the role of tree mortality in shaping ecosystem functional properties, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19109, https://doi.org/10.5194/egusphere-egu26-19109, 2026.
Droughts and extreme precipitation alter soil and vegetation functions, but the joint responses of these two ecosystem components are not well understood. To assess how much soil and vegetation responses to precipitation changes are coupled, we collated data from more than 150 precipitation manipulation experiments where both soil (carbon and nitrogen contents, microbial biomass, respiration) and vegetation responses (biomass, nutrient contents, productivity, respiration) were assessed. We found that soil and vegetation responses were sometimes coupled, while often only soil or vegetation responded. If responses were coupled, drought tended to reduce, and increased precipitation enhance, both soil and plant storages and fluxes. In addition, drought and increased precipitation changed more often vegetation and microbial biomass than soil organic matter pools. Several response combinations were underrepresented, indicating a knowledge gap that we need to fill to quantify the coupling of different ecosystem components in the face of extreme events.
How to cite: Manzoni, S., Siegenthaler, M., Talvinen, S., Pallandt, M., Guasconi, D., Li, X., Montenegro, P., Frey, L., Varney, R., Fretzer, I., and Faticov, M.: Are soil and vegetation responses to precipitation changes coupled?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14070, https://doi.org/10.5194/egusphere-egu26-14070, 2026.
During meta-analyses, a critical stage consists of the numerical extraction of the data from the original publications. While in the medical disciplines, there are often stanard operating procedures on how exactly to extract those numbers that are then expressed as effect sizes. Because in global change ecology, we mostly lack such rules on data extraction, we often rely on the judgement of the researcher. For example, 'micro-decisions' have to be made as to what time window is averaged, or whether species are pooled or not. In an effort to create the over-arching MESI database (see van Sundert et al. 2023 GCB), amalgamating four existing data-bases, we identified a substantial 'researcher effect', which occasionally outweighs the originally observed effect of global change on ecosystems. For instance, we identified a substantial discrepancy between what different meta-analyses found in regards to the effect of rising atmospheric CO2 and warming on below ground biomass, ranging from net negative to net positive effects. Importantly, the meta-analyses are largey based on the same original data. We discuss this issue, which likely exists in other disciplines and show possible ways forward.
How to cite: Leuzinger, S., van Sundert, K., Bader, M., Hu, Y., Chang, S., Dukes, J., Langley, A., and Ma, Z.: The researcher effect can outweigh the original effect in meta-analyses of global change experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15935, https://doi.org/10.5194/egusphere-egu26-15935, 2026.
Regardless of annual rainfall amount changes, daily rainfall events are becoming more intense but less frequent across Earth’s land surfaces. Larger rainfall events and longer dry spells have complex and sometimes opposing effects on plant photosynthesis and growth, challenging abilities to understand broader consequences on the carbon cycle. Cross-scale analyses are ultimately needed to quantify responses of vegetation function to fewer, larger rainfall from different data sources, disentangle the complex driving mechanisms of the plant responses, and scale findings from field to global scales.
Here, we ask, to what degree is global vegetation function sensitive to shifts in daily rainfall frequency and intensity, especially when compared with variations in annual rainfall totals? Is global vegetation function (and terrestrial carbon uptake via photosynthesis) higher or lower in years with less frequent, more intense rainfall?
First, we collate field, model, and satellite studies that investigate the effects of fewer, larger rainfall events, while controlling for annual rainfall amounts. Plant function responses vary between -28% to 29% (5th to 95th percentile) in years with fewer, larger rainfall events compared to nominal years, with the sign of response contingent on climate; productivity increases are more common in dry ecosystems (46% positive; 20% negative), whereas responses are typically negative in wet ecosystems (28% positive; 51% negative) in years with fewer, larger rainfall events. Field scale analyses and analytical models applied to site data reveal that non-linear plant responses to soil moisture are a major mechanism responsible for these differences in sign. Second, using vegetation indices from four different satellites and a statistical approach, we draw similar conclusions about the changing sign of response across dry to wet ecosystems. Furthermore, the satellite analysis reveals that global vegetation is sensitive to daily rainfall variability across 42% of Earth’s vegetated land surfaces. Surprisingly, vegetation is almost (95%) as sensitive to daily rainfall variability as vegetation is to annual rainfall totals.
These findings across scales suggest that daily rainfall variability impacts on terrestrial ecosystems are likely having a substantial impact on the global carbon cycle and food security. Observational results, included mechanisms revealed in these analyses, are pivotal for benchmarking models and an analysis on this topic is ongoing.
How to cite: Feldman, A., Konings, A., Feng, X., Felton, A., Knapp, A., Biederman, J., Gentine, P., Cattry, M., Wang, L., Smith, W., Chatterjee, A., Joiner, J., Poulter, B., and Serbin, S.: Plant responses to rainfall frequency and intensity variations from field to global scales, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5784, https://doi.org/10.5194/egusphere-egu26-5784, 2026.
The air we breathe, the water we drink, the food we eat, and other resources we use, have resulted from interactions between the Earth’s geosphere and biosphere. Understanding these interactions is thus essential for human wellbeing, which is endangered by anthropogenically induced climate and land-use change. While contemporary anthropogenic pressures are unprecedented, the processes and natural laws governing the Earth System remain universal. Interactions between the geosphere (rocks, soils, water, atmosphere and the Earth’s surface) and the biosphere (microorganisms, fungi, plants, and animals) determine how the Earth System responds to change. Past research has largely considered geosphere and biosphere responses to Earth-System change separately. The new cluster of excellence TERRA at the Univesity of Tübingen develops an integrated understanding of how geo-biosphere interactions in terrestrial systems induce and respond to environmental changes, using evidence from both the geological past and the present to improve projections of future global change impacts and assess the effectiveness of mitigation and adaptation strategies. Understanding feedbacks between diversity and stability in the geosphere and the biosphere lies at the heart of TERRA. In particular, we hypothesize that diversity in the geosphere stabilizes the biosphere, and that vice versa biodiversity is key to stabilizing the geosphere.
TERRA represents an interdisciplinary Earth-System-Science approach. We will integrate observational, experimental, and modeling approaches spanning different periods of Earth history, incorporating the full spectrum of geological and biological sciences. We will analyze past geo-biosphere interactions preserved in geological records to elucidate how the Earth System responded to conditions that have not yet been encountered in historical times but may be encountered in the future. A mechanistic understanding of processes will be achieved by studying contemporary geo-biosphere interactions on different spatial scales. The newly established Diversitorium will facilitate field and laboratory experiments where the diversity of one sphere is selectively manipulated to study effects on the other sphere. Synthesis across spatio-temporal scales will be provided by developing and advancing integrative models merging machine learning and process-based approaches. These models will be used to evaluate the effectiveness of mitigation and adaptation measures to cope with global change.
How to cite: Dippold, M. A., Rehfeld, K., and Cirpka, O.: Terrestrial Geo-Biosphere Interactions in a Changing World: Concepts, Challenges, and Opportunities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11533, https://doi.org/10.5194/egusphere-egu26-11533, 2026.
Shrub–grassland (SGL) ecosystems cover over 40% of Earth’s vegetated land and play a crucial role in regulating the global carbon cycle, yet their large-scale responses to recent warming remain poorly constrained. Here we integrate satellite-derived gross primary productivity (GPP) and fire emissions with top-down estimates of net biosphere production (NBP) from OCO-2 XCO₂ inversions using the GCASv2 assimilation framework to quantify latitudinal trends in SGL net ecosystem production (NEP) from 2015 to 2024.
We find a clear latitudinal divergence in carbon dynamics. NEP has increased in equatorial SGLs but declined in mid-latitude regions. In equatorial areas, persistent increases in GPP surpass modest rises in total ecosystem respiration (TER), resulting in net carbon gains. In contrast, mid-latitude ecosystems experience stronger increases in TER, particularly heterotrophic respiration (Rh), than in GPP as temperatures approach the optimal range for Rh (15–23 °C). This imbalance leads to net carbon losses.
These findings reveal nonlinear, hydrothermal-threshold-driven carbon responses across SGL biomes and emphasize the need to incorporate such temperature–moisture constraints into Earth system models to improve projections of future carbon–climate feedbacks.
How to cite: Li, H., Jiang, F., and Dong, G.: Temperature Thresholds Drive Latitudinal Divergence In Herbaceous Ecosystem Carbon Balance, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1555, https://doi.org/10.5194/egusphere-egu26-1555, 2026.
Ecosystem respiration (Re) plays a critical role in the global carbon cycle, but is conventionally modelled with temperature response functions that do not adequately account for the limiting effects of high temperature on Re. Using Re data from the FLUXNET2015 network, we compared the conventional exponential temperature response function with a unimodal function that incorporates these effects. We found that the conventional function significantly underestimates the sensitivity of Re to temperature, potentially leading to overestimation of future carbon emissions. The activation energy (Ea) estimated by the unimodal function averaged 0.97 ± 0.44 eV, substantially higher than the 0.58 ± 0.27 eV calculated by the exponential function. The temperature threshold (Tth) for Re inhibition was identified at an average of 26.58°C across biomes. The largest Re increase occurs under SSP585, reaching 147.85% and 153.81% for the exponential and unimodal functions, respectively, by 2100 relative to Re simulated using the exponential function in 1990. As rising temperatures push ecosystems toward their thermal optimum, greater overestimation beyond the divergence threshold in SSP585 reduces the difference between the two functions compared to SSP245 and SSP370. These findings emphasize an underestimated temperature dependence and inaccurate trends in ecosystem respiration, highlighting the necessity of integrating high-temperature inhibition effects into Re models to improve projections of carbon dynamics.
How to cite: Liu, Z., Chen, J., Chen, B., and Wang, S.: Temperature constraints of terrestrial ecosystem respiration in global biomes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2730, https://doi.org/10.5194/egusphere-egu26-2730, 2026.
Subtropical forests play a crucial role in the global carbon cycle, yet their carbon sink capacity is significantly constrained by phosphorus availability. Models that omit phosphorus dynamics risk overestimating carbon sinks, potentially undermining the scientific basis for carbon neutrality strategies. In this study, we developed TECO-CNP Sv1.0, a coupled carbon-nitrogen-phosphorus model based on the Terrestrial ECOsystem (TECO) model, which explicitly captures key biogeochemical interactions and nutrient-regulated carbon cycling. The model simulates how plant growth and carbon partitioning respond to both external soil nutrient availability and internal physiological constraints, enabling plant acclimation to varying nutrient conditions. Using observations from a phosphorus-limited subtropical forest in East China, we first evaluated the model’s performance in estimating state variables with empirically calibrated parameters. Compared to the C-only and coupled C-N configurations, the CNP model more accurately reproduced the observed pools of plant and soil C, N, and P. To systematically optimize model parameters and reduce uncertainties in predictions, we further incorporated a built-in data assimilation framework for parameter optimization. The CNP model with optimized parameters significantly improved carbon flux estimates, reducing root mean square errors and enhancing concordance correlation coefficients for gross primary productivity, ecosystem respiration, and net ecosystem exchange. By explicitly incorporating phosphorus dynamics and data assimilation, this study provides a more accurate and robust framework for predicting carbon sequestration in phosphorus-limited subtropical forests.
How to cite: Wan, F., Bian, C., Weng, E., Luo, Y., Huang, K., and Xia, J.: TECO-CNP Sv1.0: a coupled carbon-nitrogen-phosphorus model with data assimilation for subtropical forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7603, https://doi.org/10.5194/egusphere-egu26-7603, 2026.
Under the global trend of increased vegetation growth due to global warming, spring vegetation in South Korea and East Asia has shown a pronounced greening trend since the 2000s. Interestingly, during the same period, soil moisture in South Korea during the summer season has exhibited a distinct drying trend. This study confirms through observations and model experiments that these two trends may not be simply coincidental. Instead, they could be the result of the advancement of vegetation growth onset due to the warming trend, leading to increased spring vegetation and evapotranspiration, subsequently resulting in reduced summer soil moisture. The negative correlation between spring vegetation and summer soil moisture has linearly strengthened from the late 20th century to the present.
In the 2000s, while the variability of summer soil moisture has decreased, the impact of spring vegetation variability on summer soil moisture has been confirmed to increase. CLM5 (Community Land Model 5) Model experiments conducted to verify the mechanism of the changing relationship between spring vegetation and summer soil moisture have shown that an increase in spring vegetation leads to increased evaporation the following month, followed by a decrease in soil moisture the subsequent month, consistent with observations. Furthermore, it has been confirmed that with the projected increase in insolation forcing in the future, the East Asian summer monsoon will intensify, and overall summer precipitation in South Korea is expected to increase. However, it has also been confirmed that the greening trend of vegetation may consistently contribute to the occurrence of summer droughts. Therefore, it is essential to consider the interaction with vegetation when predicting and addressing future drought changes.
How to cite: Kim, H.-N., Kim, M.-S., Woo, S.-H., and Jeong, J.-H.: Possibility of Summer Drought Due to the Recently Reinforced Growth of Vegetation in Spring in Korea , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8464, https://doi.org/10.5194/egusphere-egu26-8464, 2026.
Due to land-use change and the abandonment of mountain pastures, green alder (Alnus alnobetula (Ehrh.) K. Koch; former Alnus viridis (Chaix) DC.) has been reported to invade abandoned grassland in the Alps on a wide scale. Once restricted to north-facing slopes, with high water availability, it is now expanding into sites with impaired water availability. To identify possible restrains for a further expansion of the species, we evaluated drought tolerance using a greenhouse experiment where saplings were exposed to drought periods of different lengths, monitoring transpiration (E) and maximum (Fv/Fm) and effective (ϕ) quantum yield of photosystem II. E declined markedly once volumetric soil water content (SWC) dropped below 10%. After reirrigation E recovered quickly, but remained reduced for several weeks, indicating a post-drought legacy effect. Fv/Fm was rather insensitive to drought showing no significant changes until SWC fell below 5%. However, in correlation with photosynthetically active radiation (PAR), ϕ proved to be a useful indicator to detect moderate drought stress. When the plants were exposed to a second drought period, E reacted more sensitive to reduced soil water availability and was significantly reduced at a moderate SWC of 28%. Fv/Fm also showed an early decline at SWC of 15%, both indicating a short-term adjustment in stomatal regulation induced by the first drought. Plants lost 70% of their leaves after 12 days of SWC < 15% in the first drought. However, about 6 days after re-irrigation they started to grow new leaves. After the second prolonged drought the saplings had lost most leaves and less than a quarter survived the following winter. Green alder has shown the capacity to adapt to moderate drought, indicating a potential to persist on drier sites.
This research was funded in whole by the Austrian Science Fund (FWF) (Grant-DOI: 10.55776/P34706).
How to cite: Gruber, A., Wieser, G., and Oberhuber, W.: Physiological Responses of Green Alder (Alnus alnobetula) to Drought, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17116, https://doi.org/10.5194/egusphere-egu26-17116, 2026.
Interactions between the living and non-living components of the Earth system—the biosphere and the geosphere—are the prerequisites for a habitable planet and provide the resources required by humans. Although the scale of anthropogenic global change is unprecedented, the fundamental laws of nature governing the responses of the geo- and biosphere remain unchanged. The TERRA Cluster of Excellence will investigate how geo-biosphere interactions respond to and influence environmental change. TERRA tests the hypothesis of whether the geosphere’s diversity stabilizes the biosphere and, vice versa, whether biodiversity stabilizes the geosphere – and asks: if this is the case, how? To target this challenge, one primary goal of TERRA will be to generate a discipline-overarching concept on system’s stability, applicable to the geo- and the biosphere, to quantitatively integrate the stability concept into predictive models. Based on that, the quantitative description of diversity-stability interrelationship within and across spheres is the overarching goal of TERRA.
TERRA’s four research themes are organized along the continuum of different temporal and spatial scales. Theme 1 “Geo-Biosphere Interactions in the Geological Past” involves investigations at sites where high-fidelity records of past geo-biosphere interactions are well preserved across key time intervals. In one project, we will focus on the paleo-biodiversity hotspot at the Miocene site Hammerschmiede in Southern Germany. Understanding past Geo-Biosphere Interactions provides the baseline of geo-biosphere interactions without anthropogenic influence, and thus a foundation for identifying and quantifying anthropogenic impacts under contemporary and future conditions.
Theme 2 “Large-Scale Contemporary Geo-Biosphere Interactions” develops a process-based understanding of present-day geo-biosphere interactions on spatial scales on which experimental manipulation is impossible. In our initial projects we aim to disentangle Geo-Biosphere Feedbacks in the FynBOS biome, a mediterranean biodiversity hotspot, and will assess how anthropogenically-enhanced species invasion can be analyzed as “local experiments” to understand self-organizational patterns in novel ecosystems.
Theme 3 focuses on “Small-Scale Contemporary Geo-Biosphere Interactions” to provide mechanistic understanding of feedbacks between the geo and the biosphere on scales small enough to allow well-controlled experiments (µm to 100 m). The central field plots of our Diversitorium infrastructure form a large geodiversity manipulation experiment, modulating mineralogy, texture and climate variability independently. We will, in first projects, also investigate sites with high spatial geological heterogeneity, such as Alpine peatlands, to assess how geodiversity shapes geo-bio-systems and their stability.
Across scales, Theme 4 “Geo-Biosphere Interactions in the Future” shall build and investigate future scenarios based on observational, experimental, and modeling results, guided by the principle of ’past extremes informing the future’. Using machine learning, climate and vegetation modelling, we aim to advance our understanding of past and present vegetation changes identifying the underlying complex and cascading series of biosphere-geosphere feedbacks. Model-based comparison of past and present Earth-System states allows deciphering systematic differences between dynamics under natural conditions and anthropogenic
How to cite: Abdalla, K., Cirpka, O., Rehfeld, K., and A. Dippold, M.: The TERRA approaches to unravel the interactions between the geo- and the biosphere in a changing world, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20330, https://doi.org/10.5194/egusphere-egu26-20330, 2026.
Forests provide a wide range of ecosystem services, including the provision of natural resources, regulation of atmosphere–land surface interactions, and support of social and cultural activities. Atmospheric deposition of reactive nitrogen (N deposition) represents an important nutrient input to forest ecosystems; however, most nitrogen-addition experiments fail to emulate the chronic, canopy-level inputs that occur under real-world conditions. Across the Alps, total nitrogen deposition has steadily declined since the late 1980s, but current annual deposition remains at medium to high levels (on average ~15 kg N ha⁻¹ yr⁻¹). Understanding how nitrogen deposition affects Alpine forests—particularly against a backdrop of declining inputs—is therefore critical for anticipating future forest functioning and ecosystem service provision. Meanwhile, most existing studies examine the effects of nitrogen deposition on a limited number of forest functions, implicitly assuming that, after accounting for (a)biotic drivers, residual variation in the focal functions is independent of other, unexamined forest functions. Given the complexity of forest ecosystems and the exchange of mass and energy across ecological processes, this assumption of independence of intrinsic interactions among forest functions is likely violated, potentially leading to biased inference. Here, we leverage long-term Swiss forest inventory data spanning broad environmental gradients and jointly model 13 forest functions within a multivariate framework that explicitly captures trade-offs and latent relationships among functions. We show that inference on the effects of nitrogen deposition differs substantially between univariate and multivariate models, including a sign flip of the inferred impact of nitrogen deposition on some key functions (such as bird diversity). Our results highlight the importance of viewing forests as emergent ecosystems and demonstrate that multivariate approaches provide a suitable basis for assessing global change effects. By integrating expert-based evaluations of the relative importance of individual forest functions to different ecosystem services, we further quantify the marginal impacts of historical nitrogen deposition on forest ecosystem services, offering insights directly relevant to forest management and policy.
How to cite: Chen, L., Lever, J., Anthony, M., Grossiord, C., Luo, Y., Niu, S., van der Plas, F., Stocker, B., and Gessler, A.: Investigating the impact of nitrogen deposition on the emergent forest ecosystem, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16694, https://doi.org/10.5194/egusphere-egu26-16694, 2026.
Understanding how rainfall alleviates vegetation water stress is critical for predicting ecosystem functioning in semi-arid regions under future climate conditions. This study quantifies vegetation water stress relief using the Crop Water Stress Index (CWSI) over the past 24 years in the Wanna Munna Flats of the Pilbara Basin, Western Australia, a semi-arid region characterized by a mean annual precipitation of 381 mm, a mean air temperature of 24 °C, and a potential evapotranspiration of approximately 2850 mm.
A modified Run Theory framework was employed to characterize individual stress relief events, defined as deviations of a reconstructed CWSI time series for a representative woody species (Mulga, Acacia aneura) from a reference stress condition (mean CWSI = 0.68). The results indicate that this woody species experiences persistent water stress, with a long-term mean CWSI of 0.52. In total, 191 stress relief events were identified over the 24-year study period.
On average, a relief event persists for 19 days (interquartile range: 8–36 days) and exhibits a relief magnitude of 1.9 CWSI·stress·day (range: 0.7–6.1), generated by 13.4 mm of cumulative precipitation (range: 3.8–42.6 mm) distributed over several days. Event-scale cumulative precipitation is the dominant control on both relief magnitude and duration. However, for comparable annual precipitation totals, higher rainfall intensity reduces stress relief efficiency.
Random Forest analyses further indicate that vegetation growth responses are primarily triggered by stress relief events associated with precipitation exceeding 17 mm, which account for 41.9 % of all recorded events. A pronounced step change in stress relief occurs when event-scale precipitation exceeds 56 mm, although only 42 such events were observed during the 24-year period.
Overall, this study provides a quantitative framework for characterizing water stress relief dynamics and reveals the nonlinear vegetation responses to rainfall in natural semi-arid ecosystems.
How to cite: Liu, Z., Skrzypek, G., Batelaan, O., and Guan, H.: Vegetation water stress relief by rainfall pulses in a semi-arid region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8692, https://doi.org/10.5194/egusphere-egu26-8692, 2026.
Increased diffuse radiation is known to enhance plant photosynthesis instantaneously, yet its role in regulating photosynthetic light acclimation over long-term remains elusive. Using global eddy-covariance observations and the accompanied diffuse and direct radiation measurements, we investigated how diffuse radiation controls canopy-scale light acclimation rates across diverse ecosystems. Our results showed that the maximum photosynthetic assimilation rate (Amax) is on average 40% higher under diffuse than direct radiation, consistent with the instantaneous diffuse radiation fertilization effect. As for light acclimation, we found the acclimation rate driven by diffuse light (1.8 μmol m⁻² s⁻¹ per mol photon m⁻² d⁻¹) is more than twice those under direct light (0.8 μmol m⁻² s⁻¹ per mol photon m⁻² d⁻¹). Statistical analysis showed that diffuse radiation fraction is important in determining canopy-scale light acclimation rate. The benefits from diffuse light on light acclimation weakened under high air temperature and elevated vapor pressure deficit but increased strongly with absorbed light. These findings demonstrate that diffuse radiation enhances ecosystem photosynthesis not only instantaneously but also by accelerating long-term light acclimation. Given ongoing changes in atmospheric aerosol loading and cloud cover, accounting for this photosynthetic acclimation effect of diffuse light is essential for improving predictions of terrestrial carbon uptake under changing atmospheric conditions.
Keywords: Light acclimation rate; FLUXNET; diffuse fertilization effects
How to cite: Gui, X. and Luo, X.: Evidence for widespread and strong canopy photosynthetic acclimation to diffuse light, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8737, https://doi.org/10.5194/egusphere-egu26-8737, 2026.
Climate change and management practices influence crop allocation of carbon (C), and consequently can alter grain yield and the magnitude of C sequestration (or release) from agroecosystems. However, few in situ longitudinal studies are available to quantify these changes. Here, we combined the results from 13 years (from October 2007 to September 2020) of eddy covariance data and detailed crop production measurements to investigate changing climate and C allocation in a typical wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping agroecosystem in the North China Plain. We found that the agroecosystem on average acted as a slight C sink, i.e., net ecosystem carbon balance (NECB) is 36 g C m-2 yr-1) across the study period. Increased CO2 led to a rising trend of gross primary production (GPP, 72 g C m-2 yr-2), ~35% of which led to increased NECB (the slope is 25 g C m-2 yr-2). However, concomitant increases in temperature and decreases in surface soil moisture caused higher partitioning of GPP to autotrophic respiration, leading to lower increases in net primary production and grain yield. Summer maize experienced a greater risk of C source increase, as well as greater grain yield reduction than winter wheat, most likely due to higher temperatures and drought in summer. Overall, our observational evidence suggests that current management and ongoing climate change increase the ability of the agroecosystem to increase NECB, but does not enhance crop production in this intensively managed high yield agroecosystems. However, C allocation strategies are unlikely to maintain constant in the future as multiple climate change factors act on the agroecosystem.
How to cite: Liu, F., Zhang, Y., Shen, Y., and Li, H.: Achieving grain security and carbon neutrality: Challenges from carbon allocation , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9066, https://doi.org/10.5194/egusphere-egu26-9066, 2026.
Climate-induced interannual volatility in crop production poses a growing threat to global food security, underscoring the critical need to enhance agricultural resilience alongside maintaining reliable food supplies. Although soil organic carbon (SOC) sequestration is advocated as a nature-based solution for climate adaptation, quantifying its stabilizing benefits remains constrained by small-scale in-situ trials, simplistic linear assumptions and confounding environmental factors in previous studies.
Here, we integrated two decades (2001-2020) of high-resolution remote sensing data with a two-stage analytical framework to quantitatively characterize the stabilizing effect of SOC across China’s maize and wheat croplands. Vegetation indices (NIRv), Solar-Induced Chlorophyll Fluorescence (SIF), and MODIS gross primary productivity (MODIS GPP) were used as proxies for crop productivity, while their detrended interannual coefficient of variation (CV) served as a measure of stability. First, the generalized additive mixed model (GAMM) and XGBoost model are utilized in parallel to evaluate relationships between SOC content and crop productivity stability. Across model types, results consistently shows that maintaining higher SOC content in croplands is more beneficial for crop to buffer from external volatility. We observed critical thresholds of SOC content (maize: 10.2 – 13.4 g/kg; wheat: 8.6 – 9.9 g/kg), above which high SOC leads to more stable crop productivity. Furthermore, after determining the relationships, we employ causal forest double machine learning models (CF-DML) to isolate the marginal causal effect of SOC. Results indicate that increasing unit (g/kg) SOC can reduce the CV of crop productivity by 1.09% to 2.08% on average nationally. Specially, in regions with lower SOC levels, the marginal benefits of increasing SOC are more pronounced, particularly in areas characterized by lower soil structure and greater climate variability. In these environment-limited croplands, increasing SOC can play a more significant role in maintaining sustainable agriculture.
Our results emphasize SOC’s role in building resilient food systems. This improved understanding can refine the representation of soil carbon in earth system models and highlight the importance of soil carbon sequestration in croplands under climate change.
How to cite: Huang, Y., Shi, Z., and Chen, S.: Non-linear thresholds and spatial heterogeneity define the stabilizing benefits of soil organic carbon on the stability of crop productivity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11436, https://doi.org/10.5194/egusphere-egu26-11436, 2026.
Terrestrial ecosystems currently absorb a substantial proportion of anthropogenic carbon dioxide (CO₂) emissions, yet the persistence of this land carbon sink under accelerating climate change remains largely uncertain. While process-based vegetation models project continued enhancement of carbon uptake through CO₂ fertilization, there are growing observational evidence that suggests that climate extremes, particularly 3oC global warming level, may substantially constrain or reverse these gains through droughts and heatwaves. Recent global carbon budget assessments also show a rapid weakening of the land carbon sink, with dynamic global vegetation model ensembles and atmospheric inversions indicating a large decline in net land uptake between 2022 and 2023. Here we present an observation-constrained, species-specific quantification of global terrestrial carbon fluxes across major terrestrial biomes. We integrate a combination of satellite-derived vegetation indices, a geo-referenced global database of climate-induced tree mortality, and dynamic global vegetation models from the TRENDY intercomparison models to map spatial and temporal variability in carbon uptake, storage, and loss under historical and future climate conditions. Model simulations are forced with regionally downscaled climate projections and explicitly constrained using observed mortality signals to quantify the effects of CO₂ fertilization. Our results reveal a widespread divergence between modelled and observation-constrained carbon fluxes, with some biomes exhibiting a reduced carbon sink. Species adapted to moderately moist climate conditions show strong sink-to-source transitions, while drought-tolerant species exhibit greater resilience but limited long-term sequestration capacity. These findings demonstrate that climate extremes impose substantial limits on terrestrial carbon sequestration. By linking species-level ecological responses with carbon flux dynamics, our study provides a more realistic assessment of the future role of terrestrial ecosystems in regulating the global carbon cycle under ongoing climate change, as well as show species and regions for optimal sequestration.
Key words: Carbon Flux, Carbon Dioxide Removal, Biomes, Dynamic Vegetation Models, Drought, Heatwave
How to cite: Lawal, S. and Stewarts, W.: Mapping Global Carbon Flux in Species across Terrestrial Biomes Under Climate Extremes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14745, https://doi.org/10.5194/egusphere-egu26-14745, 2026.
Global nitrogen deposition has escalated steadily since the 1980s, peaking around 2015 before stabilizing. However, global atmospheric chemical transport models often underestimate their magnitude, limiting the accurate assessment of their impact on terrestrial gross primary productivity (GPP). In this study, we elucidated the drivers of interannual GPP variability and quantified the contribution of nitrogen deposition from 1980 to 2020 using the latest global nitrogen deposition dataset, the TRENDY GPP products, and an interpretable machine learning framework (SHAP). Our findings revealed a consistent expansion in global GPP over the past four decades, averaging 156.95 ± 6.4 Pg C yr⁻¹. Intriguingly, although nitrogen deposition has recently plateaued, its relative influence on GPP has increased. Although climatic factors, primarily temperature and precipitation, dominate interannual GPP fluctuations across plant functional types (PFTs), nitrogen deposition explains 6.5% ± 3.6% of global variability. Notably, its impact is disproportionately pronounced in shrublands, savannas, grasslands, and croplands. Specifically, nitrogen enrichment stimulated GPP in grasslands and croplands but had an inhibitory effect in tropical forests. We identified a non-linear, hump-shaped response of vegetation to nitrogen loading, with an ecological threshold of 13.4 kg N ha⁻¹ yr⁻¹, beyond which the stimulatory effects diminished. Furthermore, the direct effect of nitrogen deposition on GPP outweighed its synergistic interactions with climate and CO₂, suggesting that nitrogen availability independently modulates terrestrial carbon sinks. This study underscores the biome-specific sensitivities to nitrogen loading and highlights the necessity of incorporating nitrogen saturation thresholds into the predictions of ecosystem feedbacks to global change.
How to cite: Chen, S., Chen, B., and Wang, S.: Sensitivity of Global Terrestrial Gross Primary Productivity to Nitrogen Deposition Changes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4148, https://doi.org/10.5194/egusphere-egu26-4148, 2026.
Boreal peatlands are important continental reservoirs of carbon and other elements. Changes in climate, especially increasing temperatures and more variable precipitation, alter oxidation-reduction (redox) conditions and fluxes of atmospheric and aquatic pollutants from peatlands. Here, we measure the effect of warming and elevated carbon dioxide on the speciation of sulfur in boreal peatland soil and outflow water over three years. In whole ecosystem warming experiments, with temperature levels of +0 °C (control), +2.25 °C, +4.5 °C, +6.75 °C, and +9 °C above ambient, water table height was negatively correlated with warming. Warming was correlated with changes in the size of sulfur pools, specifically, sulfur content (weight%) decreased in soils and sulfate (SO 4 2- aq) concentrations increased in outflow. Reflecting the warmer and drier conditions, the percentage of oxidized sulfur in soil, as
measured by X-ray absorption near edge structure (XANES) spectroscopy, increased with warming. Sulfur speciation in soil showed increases in ester-sulfate (R-O-SO 3 - ) content at the expense of organic disulfide (R-S-S-R’) content. In contrast to the soil, the percentage of oxidized sulfur decreased in outflow with warming. The changes in sulfur speciation in outflow were characterized by increased organic monosulfide (R-S-R’, R-S-H) content at the
expense of ester-sulfate. Overall, the peatland sulfur pools are becoming more oxidized in the soil and more chemically reduced in the outflow water in response to soil and air warming. The connection between these opposite redox trends is likely due to enhanced microbial activity in porewaters and outflow with warming. Specifically, we observed that ester-sulfate partitions from soil to outflow waters during heavy rainfall periods (based on weekly
precipitation). We surmise that increases in ester-sulfate in outflow make it available for microbial sulfur reduction processes that are also enhanced at warmer temperatures. Our study indicates that the peatland response to climate warming is complex: oxidation of sulfur in soil and the chemical reduction of sulfur in the outflow water are both correlated with warming. Notably, no significant effect of elevated carbon dioxide on sulfur pools was detected. Our findings are consistent with a net export of organic sulfur from the peatland to receiving surface waters. Furthermore, the overall loss of sulfur from this peatland is consistent with enhanced decomposition and increased plant available nutrients reported previously for this whole ecosystem warming experiment. Warming-induced changes to sulfur pools in peatlands affect the fluxes of other constituents, such as organic carbon and the pollutant methyl-mercury, that have downstream consequences for climate and water quality.
How to cite: Toner, B., Pierce, C., Jedinak, S., Stewart, B., Randall, K., Sebestyen, S., Griffiths, N., and Gutknecht, J.: Sulfur Redox Status in Peatland Soil and Outflow Waters Diverge with Climate Warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21875, https://doi.org/10.5194/egusphere-egu26-21875, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 2
EGU26-17076 | Posters virtual | VPS5
Apple Flowering Response to Climate Variability along the Himalayan Elevation GradientTue, 05 May, 14:18–14:21 (CEST) vPoster spot 2
Apple flowering in the Himalayan region depends on winter chill and spring heat, which are changing under a warming climate. These changes have increased uncertainty in flowering intensity and timing across different elevations. In this study, high-resolution UAV imagery and a YOLOv8-based segmentation model were utilized to map tree-level flowering intensity across three apple orchards situated along an elevation gradient in the northwestern Himalayas. The YOLO model was found to reliably detect flower clusters and showed strong agreement with manual counts, with an R² value of 0.85. This allowed consistent comparison of flowering intensity across sites. The winter chill was estimated using the Dynamic Model, expressed as chill portions derived from ERA5 Land hourly temperature data. Spring heat accumulation was quantified using growing degree days. Flowering varied clearly with elevation. Mid-hill orchards bloomed earlier and showed lower visible flowering during UAV surveys. Higher-elevation orchards bloomed later and exhibited higher flowering intensity. The winter chill was sufficient at all sites. Flowering responses were mainly controlled by the combined effects of chill and spring heat. The results demonstrate that integrating UAV-based deep learning with climate indices provides a practical framework to assess climate-driven changes in apple phenology in mountain environments. This approach can support climate risk assessment and adaptive orchard management in the face of continued warming.
How to cite: Shukla, Y., Gupta, V., and Himanshu, S. K.: Apple Flowering Response to Climate Variability along the Himalayan Elevation Gradient, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17076, https://doi.org/10.5194/egusphere-egu26-17076, 2026.
