This session features contributions that integrate the physical sciences and plant physiology to advance understanding of how microclimate variation influences plant functioning from molecules to the biosphere. Topics may include model development and testing, observational or experimental data, and interdisciplinary approaches that quantify or predict microclimate dynamics or physiological responses to climate extremes. Submissions focusing on energy balance, canopy structure, heat tolerance or acclimation, or novel modelling or measurement techniques are particularly encouraged.
To address climate change and the growing frequency of heatwaves and droughts, several dual-land solutions have been proposed - including agroforestry, agrivoltaics, and downstream hedgerow systems - which integrate trees, photovoltaic panels, or hedgerows with agricultural crops. At a short time scale, such configurations protect crops from excessive sunlight and strong winds, while at a longer time scale, they improve water conservation, thus enhancing crop thermoregulation during heatwaves and droughts (Barron-Gafford, et al., 2019). To accurately predict the level of protection provided, two key challenges arise: (1) modeling the impact of hedgerows, trees, or panels on the microclimate; and (2) assessing how the modified microclimate influences vegetation energy and water balances.
To this end, the considered approach leverages the Computational Fluid Dynamics software code_saturne, which enables three-dimensional simulations of how obstacles alter the microclimate quantities. Vegetation effect on airflow is represented using source and sink terms following (Katul, et al., 2004, and Vernier, et al., 2026b), while the soil–plant–atmosphere continuum model developed by A. Tuzet is used to estimate plant energy and water balances, together with photosynthesis, and water stress (Tuzet, et al., 2003, and Vernier, et al., 2026a) (see Figure below). More recently, three-dimensional energy, water, and radiation balances at the leaf-agglomerate scale have been implemented into code_saturne to better simulate the influence of trees on the microclimate, and improve the accuracy and details of tree temperature estimations.
The key drivers of plant temperature are simulated: incident radiation, convective exchange coefficient, stomatal conductance, together with air temperature and humidity. As illustrated in the Figure below, two heterogeneity scales are observed: a large one at the canopy level, and a small one at the tree level. On the one hand, trees attenuate wind speed by a factor of three between the inflow and the canopy flow, increasing convection resistance from approximately 15 s/m at the first trees with respect to the inflow to approximately 30 s/m for a tree at the center of the canopy. Alongside an approximate 1°C increase in air temperature, the first trees with respect to the inflow are about 2°C cooler than those located at the center of the canopy. On the other hand, part of each tree absorbs radiation while another one remains shaded, either by its own structure or by neighboring trees. This results in heterogeneous stomatal conductance at the tree scale, and, consequently, differences in plant temperature of more than 5°C.
The next step consists in evaluating how combining trees, crops, hedgerows, and photovoltaic panels can help mitigate the impacts of heatwaves and droughts on agricultural production. Simulations of such systems are compared to measurements conducted at experimental agrivoltaic power plants, integrating photovoltaic panels above grapevines and apple trees, or obtained from agricultural fields located downstream of hedgerows. The ultimate goal is to optimize the geometry of panels, hedgerows, and trees to maximize their protective benefits, thereby boosting agricultural productivity and strengthening resilience to climate change.
How to cite: Vernier, J., Edouard, S., Dupont, E., Trotin, V., Combes, D., and Massin, P.: 3D plant modeling to better assess heat impacts on vegetation in heterogeneous microclimates., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4226, https://doi.org/10.5194/egusphere-egu26-4226, 2026.
The ecological importance of variation in both leaf microclimates and leaf energy balance traits in determining leaf temperatures and transpiration rates has been recognized for over fifty years. However, although leaf temperature emerges at the leaf or branch scale, most studies rely on either macro- (regional) or meso- (plot) scale estimates of air temperature, which may meaningfully differ from leaf temperatures. Critically, feedbacks between microclimate and energy balance leaf traits (e.g. leaf width, stomatal regulation, leaf absorptance of shortwave radiation) on forest temperature responses are generally ignored. Here we investigate whether such feedbacks might be important by testing for covariance between leaf energy balance traits and microclimate in a tropical forest in central eastern Amazonia. We use a unique dataset of leaf traits (400+ leaves from 39 individual trees of 10 most abundant species) accessed via climbing techniques across height and light gradients from the bottom to the top of the canopy. We ask: (1) is there covariance of leaf traits with microclimate (e.g. are leaves in light gaps narrower, with smaller boundary layers, and hence more tightly coupled to air temperature, than shaded leaves)?; and (2) if so, what impact may this covariance have on the distribution of leaf temperatures in the forest canopy? Using generalized linear mixed models, we found substantial covariance of leaf widths with both height and light (proxies for microclimate variation), with height and light strongly interacting to affect leaf width (and so leaf temperature via boundary layer conductance). We then used energy balance modeling to compare simulated leaf temperatures with and without covariance of leaf width and microclimate. This work shows that leaf-environment interactions have significant effects on leaf temperatures with important implications for forest temperature sensitivity and function.
How to cite: Prohaska, N., Ziccardi, L., Wang, Y., Silva Campos, K., Restrepo-Coupe, N., Stark, S., and Saleska, S.: Co-variation of leaf traits and microclimate across canopies: does it matter for forest function?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18686, https://doi.org/10.5194/egusphere-egu26-18686, 2026.
Recent advances in stomatal optimization theory propose that under extreme heat, plants may prioritize thermal regulation over instantaneous carbon gain, leading to a decoupling of stomatal conductance (gs) from photosynthesis (A). In this framework, transpiration (E) is maintained to facilitate evaporative cooling even as A declines. However, the thermal benefit of transpiration is physically constrained by the leaf boundary layer and its sensitivity to wind speed, a factor often overlooked in standard leaf gas exchange measurements.
We explore how leaf cooling capacity is modulated by the boundary layer conductance in irrigated grapevines exposed to a temperature gradient (20°C to 40°C). Using a commercial portable gas exchange system with adjustable fan speeds, we investigate a range of aerodynamic coupling conditions. Parallel measurements with filter-paper replicas were used to independently quantify the boundary-layer conductance, and to establish a reference temperature (Tref) across fan speeds. These measurements allow us to estimate the thermal return on investment (ROI) of transpiration, defined as the reduction in leaf temperature per unit water loss (Tref-Tleaf)/E, and examine its relationship with boundary layer conductance.
By applying a unified stomatal model, we assess whether the model parameter g1, proportional to the marginal water cost of carbon gain (λ), remains constant across treatments. Finally, we propose the hypothesis that the efficacy of evaporative cooling is aerodynamically regulated, such that the thermal ROI is maximized under low-wind conditions where thick boundary layers enhance the relative contribution of latent heat. Conversely, we aim to demonstrate how high-wind conditions, typical of standard gas-exchange cuvettes, may decrease the thermal ROI by allowing convective heat exchange to dominate. We discuss how these mechanisms might mask the adaptive significance of "wasteful" water-use strategies in decoupled canopy environments.
How to cite: Asensio, D., Yousaf, A., Tagliavini, M., and Wohlfahrt, G.: Aerodynamic control of stomatal optimality: Exploring thermal cooling returns under varying leaf-to-air coupling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2140, https://doi.org/10.5194/egusphere-egu26-2140, 2026.
Vapor pressure deficit (VPD) is rising exponentially as the globe warms, while relative humidity (RH) is comparatively stable. Stomatal responses to VPD are typically studied by manipulating RH, not air temperature, creating uncertainties for future plant productivity. We tested how air temperature and RH impact the stomatal slope parameter (g1), a proxy for water-use efficiency, and whether three stomatal conductance models capture the observed effects of temperature and RH on g1, which were often positive. Only the hydraulics-based Generalized Stomatal Optimization (GSO) model correctly predicted the observed positive RH-g1 trend. Although all models predicted the observed positive temperature-g1 trends, only the GSO model captured its large magnitude as well as its interspecific variation due to differences in hydraulic traits. Our results show that dry VPD (driven by low RH) leads to hydraulic stress that increases water-use efficiency and closes stomata quickly. In contrast, hot VPD (driven by high air temperature) can lead to decreased water-use efficiency if efficient soil-to-leaf hydraulic transport is maintained and thus slower stomatal closure.
How to cite: Potkay, A., Sloan, B., Perry, A., Sperling, O., Hochberg, U., Li, R., Xu, X., Nakad, M., Peters, R., and Feng, X.: Plant hydraulics explain distinct stomatal responses to hot versus dry vapor pressure deficit, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2569, https://doi.org/10.5194/egusphere-egu26-2569, 2026.
Understanding relationships between plant heat tolerance thresholds and the environment currently is hampered by significant variation around the means, which masks potentially important information. Rather than relating to broad-scale climate measures, local adaptation of heat thresholds might occur at finer microclimatic scales, which are particularly variable in thermally extreme, heterogeneous environments, found in many alpine systems. Further, air temperatures frequently over or underestimate leaf temperatures, which are known to influence heat thresholds. Yet, a clear relationship between microclimatic conditions and heat tolerance thresholds has yet to be established. We aimed to determine the influence of prior leaf heat load on leaf photosystem heat tolerance thresholds (Tcrit) for two co-occurring alpine plant species in Kosciusko National Park, Australia: Grevillea australis and Dracophyllum continentis. Measurements were taken on five consecutive days across eight paired sites contrasting in aspect (NW, SE) at Schlink Pass (ridge line) and Mt Stilwell (cold air drainage valley). We found that Tcrit and its relationship with leaf temperature parameters, did not differ between species, locations or aspects. Traditional statistical models found that Tleaf parameters explained some variation in Tcrit; however, when pooling across sites and species, machine learning identified that 85% of the variation in Tcrit was explained by not only maximum, but also minimum leaf temperatures in the four days prior to measurement. This finding suggests that exposure to cold extremes could be conferring cross-tolerance, promoting heat tolerance acclimation. Microclimatic variation is complicated, potentially obscuring patterns that maybe present. To uncover these complex relationships between environmental conditions and plant acclimatory responses, we recommend integrating machine learning techniques with traditional statistical methods.
How to cite: Pottinger, C., Arnold, P., Danzey, L., Nicotra, A., Herdean, A., Leigh, A., and Bird, M.: Machine learning reveals that leaf temperature extremes drive shifts in plant photosystem heat thresholds across marked microclimatic variation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9216, https://doi.org/10.5194/egusphere-egu26-9216, 2026.
Experimental and modelling studies indicate that elevated CO2 (eCO2) can alter leaf thermal dynamics through reduced stomatal conductance and leaf structural trait modifications. These changes weaken evaporative cooling and shift the leaf energy balance toward higher leaf temperatures. However, empirical evidence from mature natural forest ecosystems remains limited. Thermal infrared (TIR) imaging provides a robust approach for continuous, non-contact monitoring of surface temperature in natural ecosystems. Here, we used TIR imagery to quantify canopy temperature in mature Quercus robur at the Birmingham Institute of Forest Research Free-Air CO2 Enrichment (BIFoR-FACE) facility in Staffordshire, central England, during the summers of 2021 to 2023, which included a heatwave in 2022. Elevated CO2 induced structural and physiological shifts in oak leaves, including higher leaf mass per area and lower stomatal conductance, with implications for leaf energy balance and canopy heat dissipation. Across summers, canopies in eCO2 plots were on approximately 1 °C warmer than those in ambient CO2 (aCO2) plots, with the largest differences occurring during high-temperature periods and an increased frequency of exceedance during heatwaves. We additionally assessed photosystem II heat tolerance before and during the 2022 heatwave using chlorophyll fluorescence (maximum quantum yield of photosystem II Fv/Fm). Following the July 2022 heatwave, leaves showed evidence of increased heat tolerance overall, but heat tolerance was reduced in eCO2 compared with aCO2. Together, these findings indicate that eCO2 can elevate canopy temperatures in mature temperate forest canopies and may also alter physiological heat tolerance responses during extreme heat events.
How to cite: Hagan Brown, W., Gloor, E., Fyfe, R., MacKenzie, R. J., Curioni, G., Davidson, S. J., Quick, S., Diehl, J. L., and Fauset, S.: Response of canopy temperature and leaf heat tolerance to a heatwave: a study on Quercus robur under ambient (aCO2) and elevated (eCO2) conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14586, https://doi.org/10.5194/egusphere-egu26-14586, 2026.
Amazonian forests have experienced increasingly frequent and intense droughts in recent decades, often associated with El Niño–Southern Oscillation (ENSO). These droughts have triggered complex forest responses—from increased tree mortality, reduced carbon uptake, and structural changes to increased canopy productivity—that cannot be explained by climate variability alone. While drought-related changes in light availability and physiological responses are likely to vary along the canopy profile, a key question is how drought-driven changes in canopy conditions, especially across vertical gradients, impact canopy production. To investigate this, we combined tree climbing techniques and pulse amplitude modulated (PAM) fluorometry to quantify how leaves partition absorbed photon energy across seasons and canopy strata in central Amazonian forests during typical wet and dry seasons, and throughout the 2023–2024 ENSO drought. By conducting extensive in‑canopy sampling , we show that photosynthetic efficiency and photoprotective responses differ significantly across canopy strata during drought. We found that the typical seasonal dry period had little impact on the fates of photons absorbed by leaf light-harvesting centers for a given microenvironment, consistent with multi-scale observations of sustained or high dry season canopy function in the central Amazon. In contrast, during the ENSO drought we found reduced photochemical yield in all canopy strata, with increased photoprotective heat dissipation. We also observed nonlinear relationships between photosynthetic linear electron flow between photosystems II and I and leaf fluorescence, mainly driven by the joint dynamics of PSII open reaction centers (qL) and non-photochemical quenching (NPQ). Finally, we found in situ leaf-level evidence that, in contrast to dry season resilience, drought reduces photosynthesis of large trees, driving shifts in energy partitioning from photosynthesis to photoprotective dissipation. However, yields to leaf fluorescence remained stable during drought, suggesting that extreme drought systematically alters the linkage between fluorescence and carbon assimilation. These results show that drought‐resilience mechanisms strongly modulate photosynthesis and suggest that productivity estimates based on remotely sensed sun‑induced fluorescence (SIF) alone are likely to underestimate drought responses in Amazonian forests.
How to cite: Ziccardi, L., Kramer, D., Gonçalves, N., Restrepo-Coupe, N., Taylor, T., Nelson, B., Campos, K., Siqueira-Silva, A., Prohaska, N., Albert, L., Chen, S., Saleska, S., and Stark, S.: Drought-induced shifts toward photoprotection reduce Amazon photosynthesis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22804, https://doi.org/10.5194/egusphere-egu26-22804, 2026.
Montane forests exhibit complex, heterogeneous microclimatic regimes that challenge the physiological plasticity of canopy and subcanopy species. In a Himalayan subalpine forest, we investigated how topographically mediated light environments shape the expression of photosynthetic traits in co-dominant trees — Quercus semecarpifolia (canopy) and Rhododendron arboreum (subcanopy)—across north- and south-facing slopes. Using leaf-level gas exchange measurements, we identified consistent patterns of light acclimation in Q. semecarpifolia and high-light-adapted R. arboreum. However, shade-acclimated R. arboreum individuals on north-facing slopes displayed idiosyncratic physiological signatures, including positive dark respiration rates (Rd) and negative light compensation points (LCP) — magnitudes theoretically implausible under standard C3 photosynthetic models.
These anomalies suggest either (i) physiological re-fixation of respired CO2 under low light, (ii) non-linear error propagation in light response curve (LRC) fitting at extremely low PPFD, or (iii) extreme photoprotective plasticity unique to shade-adapted subcanopy species. Unlike Q. semecarpifolia and light-acclimated R. arboreum on south-facing slopes, these north-facing subcanopy individuals maintained high NPQ under minimal photon flux, indicative of disproportionate energy dissipation mechanisms.
Our findings highlight how fine-scale microclimatic heterogeneity, especially in shaded montane niches, can generate unexpected and complex trait responses that deviate from established photosynthetic theory. These results necessitate refined methodological protocols and physiological models to interpret trait dynamics in low-light, high-humidity microclimates, particularly in the context of rising canopy temperatures and climate extremes. The study offers critical insights into species-specific limitations and compensations under montane microclimatic stress, with implications for predicting forest carbon cycling and resilience under future climate scenarios.
How to cite: Mishra, A., Gupta, R., Joshi, R. K., and Garkoti, S. C.: Idiosyncratic Photosynthetic Traits in a Montane Subcanopy Tree Species Under Low-Light Microclimates Reveal Microclimatic Acclimation Trade-Offs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-859, https://doi.org/10.5194/egusphere-egu26-859, 2026.
Forest canopies provide shade and generally buffer summer extremes in the understory. However, the wind attenuation and water consumption of large trees can sometimes make the understory hotter and drier than an open field. To maintain forest regeneration and biodiversity, it is crucial to identify the factors that cause forest canopies to transition from buffering to amplifying climate extremes. Structural factors such as leaf area index, crown aggregation, and canopy height are important and well-known factors that influence canopy density and understory microclimate. However, other local factors, such as the species composition and vertical complexity of the canopy, topographic convergence and water availability also influence the ability of forest canopies to attenuate summer climate extremes. In this talk, I will present an overview of how these factors influence the buffering or amplification of climate extremes individually and collectively using examples from experimental and physics-based modelling studies. I will also discuss how this influence translates to heat and water stress for understory species and tree seedlings.
How to cite: Ogee, J. and the The ANR project MaCCMic Team: Buffering of microclimate extremes in the understory and its consequences for tree seedling survival, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18728, https://doi.org/10.5194/egusphere-egu26-18728, 2026.
Multilayer canopy models, based on energy balance principles, are appropriate modeling tools for understanding and predicting the effects of hot droughts on forest productivity and leaf damage caused by extreme leaf temperatures. Leaves within canopy vertical layers are exposed to different levels of radiation and momentum flux, resulting in different leaf temperatures and leaf water potentials in the upper, middle and lower canopy. Explicit consideration of these vertical gradients enables more mechanistic predictions without reliance on empiricism and formal model calibration. Here we use two broadleaf forest sites affected by the 2012 American Midwest drought to study the CanVeg2 model’s ability to reproduce the forest canopy responses as measured from eddy covariance towers. This study relies on 3D radiative transfer simulations based on canopy structure information derived from a ground lidar instrument to characterize the radiative forcing on leaves. At both sites the forest productivity was significantly affected by the 2012 drought, as evidenced by the eddy covariance flux tower records. Images from the PhenoCam network show that at one site (Missouri Ozark) there was significant leaf die off, while the other site (Morgan Monroe, Indiana) showed no visual evidence of leaf damage, even though the air temperatures reached were higher at the Morgan Monroe site, why could that be? We will present evidence of the reasons from a modeling perspective, and discuss the conditions under which the canopy microclimate leads to leaf temperatures above critical damage thresholds, as well as where in the canopy leaves reached their highest temperatures for this specific case, and for how long. Using leaf level data on the temperature response of the maximum quantum yield of photosystem II for the species present at both sites, we also present a novel modeling approach to estimate leaf damage levels and its effect on canopy productivity for the rest of the growing season once rains return and the hot drought subsides.
How to cite: Beland, M., Bonan, G., and Baldocchi, D.: Estimating leaf damage from hot drought events and predicting the effects on forest productivity from multilayer canopy models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14569, https://doi.org/10.5194/egusphere-egu26-14569, 2026.
Variation in leaf structure and morphology impacts leaf temperature, leading to differences in leaf and canopy temperatures between species. This is a growing research area, and while the biophysical mechanisms are well described, datasets on leaf temperatures and understanding of the impact of warming on leaf thermal physiology are still developing, especially for African tropical forests. Here we present results from the Trop-heat and Rwanda-TREE projects which looked at leaf energy balance of saplings of eight species growing in common gardens at two elevations in the Nyungwe National Park. We compare leaf-to-air temperature differences for these species growing at mid and high elevation sites with mean temperatures of 22.5 °C and 17.5 °C, respectively. We then quantify how key energy-balance traits (leaf size, absorptance, stomatal conductance) change with warming, and evaluate the extent to which these traits and their temperature acclimation explain the observed leaf temperatures under higher growth temperatures. Together, this improves our understanding of the variation in leaf thermoregulation between Rwandan tree species and how leaf temperature regimes may alter under climate warming.
How to cite: Fauset, S., Hagan Brown, W., Gonzalez-Caro, S., Hartley, I., Johannson, K., Meir, P., Niyigena, E., Restrepo, Z., Rivera, V., Taylor, T., Uddling, J., Wallin, G., and Mercado, L.: The impact of heating on leaf energy balance of Rwandan forest trees: results from an elevation gradient experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21039, https://doi.org/10.5194/egusphere-egu26-21039, 2026.
Forest microclimates play a critical role in shaping biodiversity, ecosystem functioning, and species responses to climate variability. Within forested environments, near-surface air temperatures often deviate substantially from macroclimatic conditions as a result of canopy structure and seasonal vegetation dynamics. Despite growing interest in forest microclimate buffering, the fine-scale and seasonal links between forest structure and temperature regulation remain poorly quantified, particularly during phenological transitions such as spring leaf onset.
Here we show that high-resolution LiDAR-derived forest structural metrics capture rapid canopy development during leaf emergence and robustly explain spatial and temporal variability in forest temperature offsets relative to macroclimatic conditions. We combined repeated UAV-based LiDAR acquisitions conducted throughout spring 2025 with in situ microclimate measurements across four temperate forests in Wallonia (Belgium). Metrics describing canopy density and structural complexity, such as plant area index, rumple index, and canopy height skewness, characterize complementary aspects of structural development during leaf onset.
Together, these structural indicators explain a substantial fraction of the variability in forest temperature offsets and reveal seasonally evolving relationships between canopy structure and microclimate buffering. These results indicate that microclimate buffering is primarily driven by short-term structural dynamics during leaf onset rather than by static canopy properties.
Our findings advance the mechanistic understanding of how phenological dynamics modulate forest microclimates and emphasize the importance of accounting for seasonal structural variability when assessing forest resilience to climate extremes. Given the strong sensitivity of forest species and ecosystem processes to small microclimatic variations, incorporating temporally explicit canopy structure is essential for improving predictions of ecosystem responses under ongoing climate change.
How to cite: Favaro, A., Bastin, J.-F., and De Frenne, P.: Drone-based LiDAR reveals dynamic links between forest structure and microclimate during phenological transitions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10230, https://doi.org/10.5194/egusphere-egu26-10230, 2026.
Chlorophyll fluorescence, emitted mainly in the red and far-red spectral ranges (about 650–850 nm), provides direct information on photosynthetic functioning and plant stress responses. Solar-induced chlorophyll fluorescence (SIF) offers information on photosynthetic activity at the canopy scale under natural light conditions, but its interpretation is strongly influenced by variable illumination and canopy structure. Actively induced fluorescence using LED light sources offers a controlled alternative for fluorescence spectra measurements. LED-induced chlorophyll fluorescence (LEDIF) enables observations under standardized conditions, independent of ambient light variability, and allows more direct access to baseline fluorescence properties linked to plant physiological status. LEDIF is therefore well-suited for studying stress responses in controlled experiments.
In this study, controlled microcosm experiments were conducted on sunflower and wheat following the same experimental protocol to investigate plant responses to drought and heat stress using LEDIF. Plants were subjected to four treatments: well-watered – no heat stressed, well-watered – heat stressed, water-stressed – no heat stressed, and water-stressed - heat stressed. All experiments lasted approximately two months in 2024-2025, with stress applied gradually. Chlorophyll fluorescence was induced using an actively controlled 11-channel multispectral LED illumination system. Broadband fluorescence (650–850 nm) and reflectance spectra (350–850 nm) were recorded above the canopy using a downward-facing VIS–NIR spectrometer positioned between the LED panels, while canopy architecture and leaf area development were monitored using side- and top-view RGB images. LEDIF increased during canopy development of the sunflower plants, after which clear treatment-dependent responses emerged. Sudden heat stress applied to well-watered plants caused a decline in fluorescence comparable to that in gradually drought-stressed sunflower plants. While plants exhibited similar growth during the initial phase, drought induced strong divergence in canopy development, with well-watered plants maintaining healthy canopies and drought-stressed plants showing severe canopy loss. Wheat plants consistently exhibited lower fluorescence intensity than sunflower plants and a stronger temporal decline in LEDIF, reflecting greater loss of green leaf area. Leaf angle changes supported these responses, with water-stressed plants displaying shifts toward flaccid, senescing leaves.
How to cite: Guettala, I., Mészáros, Á., Balogh, J., and Fóti, S.: LED-induced chlorophyll fluorescence during heat and drought stress in microcosm experiments on sunflower and wheat, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12431, https://doi.org/10.5194/egusphere-egu26-12431, 2026.
Due to anthropogenic climate change, temperatures are increasing, placing tropical forests, including mangroves, at increased risk of heat stress. The red mangrove (Rhizophora mangle) is a salt-tolerant tree species, with ecological and social importance in the coastal regions of Panama and many other parts of the Americas. It remains unclear how heat stress interacts with seawater salinity in this species. We hypothesize that elevated temperatures reduces overall biomass accumulation and photosynthetic performance, but increases photosystem II heat tolerance through short-term acclimation, whereas increased salinity reduces these traits.
To address this question, an experimental study is currently being conducted in glasshouses exposed to full solar radiation in Panama, where red mangrove seedlings are grown under two temperature settings: ambient temperature and elevated temperature (+5 °C above ambient). Within each glasshouse, eight seedlings are grown per salinity treatment at four salinity concentrations (<0.5 ppt, 5 ppt, 20 ppt, and 35 ppt) in hydroponic systems. This study will provide insight into how the combined effects of salinity and heat influence biomass accumulation and allocation, photosystem II heat tolerance, photosynthetic gas exchange and ionic content of red mangrove seedlings.
How to cite: Krüger, C. and Winter, K.: Salt and heat: The effects of elevated temperature at different salinities on seedlings of the red mangrove (Rhizophora mangle L.), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13440, https://doi.org/10.5194/egusphere-egu26-13440, 2026.
Mediterranean forests are increasingly exposed to hotter and drier summers, yet the mechanisms by which mature trees regulate canopy temperature under chronic soil moisture limitation remain poorly constrained. We investigate ecosystem-scale drivers of canopy thermoregulation and consequences for leaf thermal safety margins and function in Quercus ilex in southern France (Puéchabon) and northeastern Spain (Prades), where throughfall exclusion has reduced soil moisture by ~30% for over two decades. Combining continuous micrometeorological measurements with seasonal observations of canopy temperature, gas exchange, sap flow, and thermal tolerance, we ask whether long-term drought acclimation alters canopy-level physiological responses in ways that modify or maintain leaf thermal safety margins. We test the hypothesis that chronic soil moisture reduction leads to reduced transpiration, resulting in warmer canopies during the growing season, but that drought-acclimated trees exhibit altered stomatal sensitivity that mitigates leaf overheating during heat waves. We further assess whether recovery of transpiration following hot periods differs between control and drought-treated trees and whether responses vary between cooler and warmer sites. This work leverages long-term field experiments to improve mechanistic understanding of tree thermoregulation under future Mediterranean climate extremes.
How to cite: Kullberg, A., Heintzelman, C., Milano, A., Vallicrosa, H., Limousin, J.-M., Ogaya, R., Peñuelas, J., Bachofen, C., and Grossiord, C.: Canopy thermoregulation of Quercus ilex under long-term soil moisture reduction across a Mediterranean climate gradient, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5738, https://doi.org/10.5194/egusphere-egu26-5738, 2026.
Accurately representing within-canopy microclimatic processes remains a major challenge for vegetation and climate models. Most Land Surface Models (LSMs) and Earth System Models (ESMs) rely on simplified canopy representations that fail to resolve the effects of vertical gradients of temperature and vapor pressure deficit (VPD), despite their critical role in regulating plant physiology, forest dynamics, and biosphere–atmosphere exchanges. While multilayer canopy models improve the representation of these gradients, they often lack the structural and demographic realism needed to link microclimate to long-term forest dynamics.
Here, we use the individual-based forest model TROLL to compare simulations that include or neglect within-canopy microclimatic buffering, and to assess its influence on physiological fluxes, forest structure, and long-term carbon storage. TROLL explicitly represents individual tree growth, mortality, three-dimensional structure, and competitive interactions, allowing environmental conditions to vary vertically and to be experienced by trees according to their position within the canopy. To disentangle short-term and long-term effects, we decompose ecosystem fluxes over the last decade of the simulations, isolating physiological and structural responses from emergent centennial-scale patterns.
Preliminary analyses suggest that microclimatic buffering affects gross primary productivity (GPP) and transpiration in contrasting ways. These metrics do not always respond in the same direction, with distinct, and sometimes decoupled, responses across vegetation layers, reflecting differences in exposure, hydraulic constraints, and trait-mediated regulation. Aboveground biomass also shows non-intuitive responses to microclimatic buffering, highlighting the limits of interpreting forest functioning from fluxes alone.
Over centennial timescales, simulations including microclimatic buffering lead to forests characterized by lower atmospheric demand, reduced hydraulic stress, and ultimately higher aboveground biomass, despite lower photosynthetic fluxes. These long-term differences emerge from the cumulative effects of short-term physiological regulation and size-dependent mortality, which selectively favors individuals less exposed to thermal and hydric stress.
By explicitly linking microclimatic buffering, ecosystem fluxes, and demographic processes, this study provides a mechanistic explanation for how within-canopy microclimatic heterogeneity can enhance forest carbon storage while dampening ecosystem-level fluxes. Our results highlight the importance of representing microclimatic buffering and individual-level processes to improve predictions of forest resilience under ongoing climate warming.
How to cite: Garisoain, R., Maréchaux, I., Ogée, J., and Chave, J.: How within-canopy microclimatic buffering shapes forest structure and function, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9835, https://doi.org/10.5194/egusphere-egu26-9835, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 2
EGU26-16813 | ECS | Posters virtual | VPS6
Plant heat tolerance across a heteregenous alpine landscape: From distribution to microclimateThu, 07 May, 14:03–14:06 (CEST) vPoster spot 2