Juan Carlos Baca Cabrera

Fructan stores constitute the most important reserve carbohydrate pools of cool season (C3) grasses, but it is largely unknown how the variation of atmospheric CO2 concentration ([CO2]) between past and projected future levels affects their function in source (photosynthesis) – sink (growth and respiration) relationships. This study addressed this question with perennial ryegrass (Lolium perenne L.) grown at [CO2] of 200, 400 or 800 μmol mol-1 with growth-limiting nitrogen fertilization. Sixty-six days-old vegetative stands were labelled with 13CO2/12CO2 mixtures for 7 days and the 13C-tracer dynamics in whole-shoot sucrose, fructans, glucose and fructose pools evaluated with a four-pool compartmental model of central carbohydrate metabolism. Increasing [CO2] from 200 to 800 μmol mol-1 increased shoot mass 1.6-fold and fructan concentration from 35% to 50% of dry weight, while decreasing the nitrogen nutrition status of stands. Conversely, [CO2] had no effect on the half-lives of water-soluble carbohydrate pools (fructans, ∼7.7 days; sucrose, glucose and fructose, 2.3-4.5 hours). Carbon cycling through the fructan pool was enhanced by [CO2], increasing the mean residence time of carbon in the carbohydrate system from 9 to 14 days between 200 and 800 μmol mol-1 [CO2]. Sucrose resynthesis from breakdown products of fructans (fructose) was extensive and corresponded to 65% and 113% of concurrent sucrose neo-synthesis (or sucrose consumption in growth and respiration) at 200 and 800 μmol mol-1 [CO2], respectively. These results imply a strong constitutive buffering of sucrose availability in the source-sink system of perennial ryegrass (and likely most other C3 grasses) by fructan metabolism.

Root hydraulic properties affect water uptake in wheat (Triticum aestivum L.) and are strongly influenced by root anatomy, yet how they vary along root axes and differ among cultivars remains underexplored. We investigated crown roots of six German winter wheat cultivars spanning one century of release, sampled from a field experiment. Roots were imaged at different positions along their axis using a high-throughput system (Rapid Anatomics Tool), and the resulting anatomical traits were coupled to the GRANAR–MECHA model to estimate radial and axial hydraulic conductance. Longitudinal anatomical gradients were pronounced: tissue dimensions, metaxylem number, and apoplastic barriers decreased from the base onwards, resulting in radial conductance increasing and axial conductance decreasing with distance from the base. Cultivar differences were also apparent: modern cultivars had smaller tissues and fewer metaxylem vessels, reducing both axial and radial conductance and lowering whole-root water uptake capacity (∼20–30%). By integrating field sampling with high-throughput image analysis and modeling, this study establishes an integrated phenotyping approach linking root anatomy to hydraulic function and uncovering anatomical traits relevant for water uptake. The results show that longitudinal gradients and cultivar-associated anatomical differences contribute to variation in hydraulic properties and persist along fully mature root segments.

Accurate representation of soil and plant hydraulic processes is crucial for predicting forest water and carbon fluxes under variable climate conditions. At the Forest Research sites across Germany, we applied an Ensemble Smoother with Multiple Data Assimilation (ESMDA) coupled with the Community Land Surface Model (eCLM; https://github.com/HPSCTerrSys/eCLM) to optimize soil and vegetation parameters. Site-specific observations included soil moisture, evapotranspiration (ET), and dynamic canopy conductance, with the latter derived from sap-flow measurements. Across all sites, ensemble simulations were performed for 2012 – 2024 using 120 ensemble members in which key parameters controlling soil hydraulics, photosynthesis, stomatal behavior, and plant hydraulics were perturbed.We tested several data assimilation configurations. Assimilating soil moisture alone improved simulated soil water content, reducing RMSE by 5–50% across soil depths, but had limited impact on ET, gross primary production (GPP), or net ecosystem exchange (NEE). In contrast, assimilating both soil moisture and ET further constrained vegetation parameters, resulting in modest improvements in ET, GPP and NEE, while maintaining a large ensemble spread that captures a high percentage of observations. Optimized soil and plant hydraulic parameters also enhanced the representation of seasonal plant water stress, capturing summer stress dynamics more realistically in both wet and dry years, with stronger hydraulic limitation during dry years.These results indicate that correcting soil water availability alone is insufficient to improve plant water use and photosynthesis. Including ET and canopy conductance observations provides additional constraints, strengthening the interactions between soil moisture, transpiration, and carbon uptake. This demonstrates that multi-variable data assimilation is needed to effectively reduce uncertainty in both soil and plant hydraulics, and that direct physiological measurements, such as sap-flow, can further enhance model predictions of both water and carbon fluxes.

Plant hydraulic traits regulate water transport in the soil–plant–atmosphere continuum and mediate the coupling between soil moisture availability, stomatal regulation, and ecosystem carbon uptake. Mechanistic representations of plant hydraulics in land surface models, such as the Community Land Model (CLM), improve the accuracy of simulated vegetation fluxes, particularly under drying soil conditions¹, but they also introduce additional parameters that can be difficult to constrain and can strongly influence model outputs. Global ensemble perturbation experiments in CLM have shown that plant hydraulic parameters are among the most influential controls on evapotranspiration, although their relative importance varies across regions². Yet, how the sensitivity of these parameters varies across plant functional types (PFTs) and seasons remains largely unexplored.In this study, we investigated the sensitivity of simulated vegetation water potential and water and carbon fluxes to five key plant hydraulic parameters, including stomatal behavior (medlyn slope), plant and root conductance (kmax and krmax), cavitation resistance (psi50) and root distribution (β) using eCLM (https://github.com/HPSCTerrSys/eCLM). Ensemble simulations were performed for 13 ICOS sites across Europe, covering four climate zones and five PFTs, over the period 2009–2018. The selected parameters were varied within PFT-dependent ranges following previous perturbation experiments²,³, resulting in a total of 336 ensemble members. Variance-based parameter sensitivities (main effects, two-way interaction effects, and total effects) were quantified using the GEM-SA global sensitivity analysis framework based on Gaussian process emulation4. Emulators were trained on monthly averages for each station and each output variable individually.Across simulations, medlyn slope and kmax showed the strongest effects on simulated water and carbon fluxes (ET, Tr, GPP, NEE) with main effects explaining more than 60% of the variance, while two-way interaction effects contributed only marginally. However, parameter sensitivities varied substantially among PFTs, with distinct patterns in the relative importance of dominant parameters for Mediterranean evergreen broadleaf forests, temperate deciduous forests, and evergreen needleleaf forests. Sensitivities also varied seasonally, with the remaining parameters—particularly psi₅₀—becoming increasingly influential under dry summer conditions. Most notably, seasonal shifts in the direction of parameter effects on canopy transpiration were detected at drought-prone Mediterranean sites: higher medlyn slope increased transpiration during spring, but led to reduced transpiration during summer, reflecting earlier stomatal closure under increasing plant hydraulic stress.Our results show that model sensitivity to plant hydraulic parameters varies across PFTs and seasons, reflecting changes in model behavior across environments. These findings motivate further model development and refinement of plant hydraulic and stomatal process representation to ensure consistent performance across seasons, especially during drought.References 1Kennedy et al. (2019). 10.1029/2018MS0015002Kennedy et al. (2025). 10.1029/2024MS0047153Eloundou et al. (2024). 10.5194/egusphere-egu24-160864O’Hagan (2006). 10.1016/j.ress.2005.11.025

Breeding has significantly improved grain yields in winter wheat ( Triticum aestivum L.). Grain yield improvements were previously attributed to changes in biomass partitioning and canopy architecture, largely based on measurements at single time points such as flowering or maturity. However, comprehensive physiological data covering the growth of modern and historic cultivars throughout the growing season remain rare. This study investigated how breeding progress influenced canopy structure and biomass partitioning across six German winter wheat cultivars released between 1895 and 2002. Field experiments were conducted over two seasons to measure aboveground biomass, root biomass, and canopy traits such as leaf area index (LAI) and specific leaf area (SLA) at multiple stages. Root biomass was assessed using large pots that were buried within an already sown field. Results showed differences in biomass partitioning patterns between cultivars and a trend toward a lower root to shoot ratio at anthesis in modern cultivars. Compared with modern cultivars, historic cultivars displayed larger flag leaves, a higher maximum LAI around flowering and a larger SLA, but similar light extinction coefficients. Significant season effects were observed, with reduced shoot biomass and increased root allocation at flowering in 2023, a year with a hot and dry spring, particularly in older cultivars. Yield increases were most strongly associated with harvest index, alongside faster phenological development and changes in biomass allocation across developmental stages. These findings provide stage‐specific insights into cultivar physiology that might help in guiding future breeding strategies.

Root hydraulic properties affect water uptake in wheat ( Triticum aestivum L.) and are strongly influenced by root anatomy, yet how they vary along root axes and interact with cultivar differences remains underexplored. We investigated crown roots of six German winter wheat cultivars spanning one century of release, sampled from a field experiment. Roots were imaged at different positions along their axis using a high-throughput system (Rapid Anatomics Tool), and the resulting anatomical traits were coupled to GRANAR–MECHA to model radial ( K _r ) and axial conductance ( k _x ). Longitudinal anatomical gradients were pronounced: tissue dimensions, metaxylem number, and apoplastic barriers decreased from the base onwards, resulting in K _r increasing and k _x decreasing with distance from the base. Cultivar differences were also apparent: modern cultivars had smaller tissues and fewer metaxylem vessels, reducing both axial and radial conductance and lowering whole-root water uptake capacity (∼20–30%). By integrating field sampling with high-throughput image analysis and mechanistic modeling, this study establishes an integrated phenotyping approach that links root anatomy to water uptake and uncovers anatomical traits relevant to hydraulic function. The results show that longitudinal gradients and cultivar-associated anatomical differences contribute to variation in hydraulic properties and persist along fully mature root segments. Highlight: High-throughput imaging–modeling shows that longitudinal gradients and cultivar-associated anatomical differences along crown roots shape radial and axial conductance, leading to reduced whole-root water uptake capacity in modern winter wheat

Breeding has significantly improved grain yields in winter wheat. Yield improvements were mainly associated with changes in biomass partitioning and canopy architecture. While many studies address physiological differences at harvest or single times during development, data covering the physiology of modern and historic varieties throughout growth are rare. This study investigated how breeding progress influenced canopy structure and biomass partitioning across six German winter wheat cultivars released between 1895 and 2002. Field experiments were conducted over two seasons to measure aboveground and root biomass and canopy traits such as leaf area index (LAI) and specific leaf area at multiple stages. Root biomass was assessed using large pots that were buried within an already sown field. Results showed differences in partitioning patterns between cultivars and a trend towards a lower root to shoot ratio at anthesis in modern cultivars. Historic cultivars displayed larger flag leaves and a higher LAI but similar light extinction coefficients. Significant years effects were observed, with reduced shoot biomass and increased root allocation in the drier year of 2023, particularly in older cultivars. Yield increases were closely related to phenology and partitioning dynamics. These findings provide stage specific insights into cultivar physiology that are essential for calibrating crop models and guiding future breeding strategies.

Root anatomical phenotyping has become a demonstrably essential part of investigating root physiology and in acquiring a holistic understanding of plant development. However, accessible high throughput methods for root anatomical analysis are still lacking. Here, we present the Rapid Anatomics Tool (RAT), a novel, low-cost system for high throughput root anatomical imaging with a shallow learning curve for obtaining high quality images suitable for comparative analysis across a number of plant species. Its efficiency comes from combining blockface-like imaging and stain-free imaging using near-ultraviolet (nUV) autofluorescence utilising a combination of low-cost commercial equipment, readily available mechanical components, and custom designed and 3D printed tools. Using this system, we investigated the anatomy of mature tissue along the axis of wheat crown roots, revealing a tendency of reduction in vascular complexity (expressed through a reduction in metaxylem number, area, and mean area per metaxylem file) from the basal to the distal region of the root. This study highlights the importance of thorough sampling strategies for investigating root anatomy in relation to organ function and introduces an accessible, relatively high-throughput method to support such research.

Wheat (Triticum aestivum L.) plays a vital role in global food security, and understanding its root traits is essential for improving water uptake under varying environmental conditions. This study investigated how over a century of breeding has influenced root morphological and hydraulic properties in 6 German winter wheat cultivars released between 1895 and 2002. Field and hydroponic experiments were used to measure root diameter, root number, branching density, and whole root system hydraulic conductance (Krs). The results showed a significant decline in root axes number and Krs with release year, while root diameter remained stable across cultivars. Additionally, dynamic functional-structural modeling using the whole-plant model CPlantBox was employed to simulate Krs development with root system growth, revealing that older cultivars consistently had higher hydraulic conductance than modern ones. The combined approach of field phenotyping and modeling provided a comprehensive view of the changes in root traits arising from breeding. These findings suggest that breeding may have unintentionally favored cultivars with smaller root systems and more conservative water uptake strategies under the high-input, high-density conditions of modern agriculture. The results of this study may inform future breeding efforts aimed at optimizing wheat root systems, helping to develop cultivars with water uptake strategies better tailored to locally changing environmental conditions.

Plants are increasingly exposed to water stress under climate change, posing significant challenges for accurate simulation of carbon and water fluxes in terrestrial ecosystems. Most land surface models simulate the regulation of water and carbon fluxes in response to soil moisture stress through empirical soil hydraulic schemes. However, these schemes often introduce significant uncertainties in water and carbon simulations. To address this, the Community Land Model version 5 (CLM5) introduced a plant hydraulic stress routine that explicitly models water transport through vegetation via a hydraulic framework, improving the representation of vegetation water potential, root water uptake, and plant water stress1. However, including plant hydraulics introduces additional parameters that are difficult to constrain due to limited field data and high variability. Understanding the influence of these plant hydraulic parameters on water and carbon flux modeling is crucial for model improvement and prediction accuracy.In this study, we used a parameter perturbation approach to investigate the role of plant hydraulic parameters at 14 experimental sites in Europe, representing diverse plant functional types (PFTs) and climate zones. Using CLM5, we performed 128 ensemble simulations per site, systematically varying three key hydraulic parameters: plant- and root-segment maximum conductance (kmax and krmax) and water potential at 50% loss of segment conductance (psi50). The perturbation ranges were informed by previous parameter perturbation experiments2,3. We evaluated: (i) how the model represented plant hydraulic dynamics (i.e., vegetation water status and plant-segment conductances), (ii) the sensitivity of carbon and water fluxes—gross primary production (GPP) and evapotranspiration (ET)—to parameter variation, and (iii) model performance compared to in-situ observations.The results showed that the model successfully captured seasonal variations in plant-segment conductance and vegetation water potential, which were reflected in the seasonal dynamics of GPP and ET. However, at drought-prone sites, the model overestimated ET reductions during summer compared to observations, due to a steep decline in root-segment conductance and stomatal closure. This highlights the need for improved parameterization of psi50 and krmax to better represent plant responses to extreme drought. In addition, ensemble simulations revealed substantial sensitivity of GPP and ET to parameter perturbations, with variations up to 50% in GPP and 30% in ET depending on PFT and climate zone. These results underscore the importance of considering the variability in plant hydraulic properties, particularly kmax and krmax, which span several orders of magnitude.To address these uncertainties, the next steps of this work will focus on refining the parameterization by integrating data on plant hydraulic traits from existing databases4,5. This approach will help constrain parameter ranges across ecosystems and climate zones, particularly for drought-prone sites. Improving the representation of plant hydraulic traits will enhance predictions of ecosystem responses to water stress and the reliability of land surface models under current and future climate scenarios.References1Kennedy et al. (2019). 10.1029/2018MS001500 2Kennedy et al. (2024). 10.22541/essoar.172745082.24089296/v1 3Eloundou et al. (2024). 10.5194/egusphere-egu24-16086 4Kattge et al. (2020). 10.22541/10.1111/gcb.14904 5Baca Cabrera et al. (2024). 10.1002/pld3.582