The functional role and genetic control of many root anatomical and architectural traits are poorly understood. Our research focuses on characterizing root traits for enhanced stress tolerance and identifying genetic mechanisms controlling the expression of root traits. We have identified a candidate gene for root cortical aerenchyma formation which mapped to a root cortex-expressed bHLH transcription factor gene. A bHLH121 Mu transposon mutant line and a CRISPR/Cas9 loss-of-function mutant exhibited reduced root cortical aerenchyma formation, whereas an overexpression line exhibited significantly greater root cortical aerenchyma formation when compared to the wildtype line in many environments. Overall functional validation of the bHLH121 gene’s importance in root cortical aerenchyma formation provides a functional marker to select varieties with improved soil exploration and thus yield. Characterization of these lines under suboptimal water and nitrogen availability in multiple soil environments revealed root cortical aerenchyma is plastic in response to abiotic stress. Our results suggest that phenotypic plasticity is highly quantitative and plasticity loci are distinct from loci that control trait expression in stress and non-stress conditions. The identification of genes and functional phenotypes of root traits will facilitate efforts for the development of novel nutrient and water efficient crop varieties.

How to cite: Schneider, H.: Genetic Control and Phenotypic Plasticity of Root Cortical Aerenchyma in Maize, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6403, https://doi.org/10.5194/egusphere-egu24-6403, 2024.

Crop breeding to increase below-ground production and inputs of organic matter into soil has been attracting increasing attention as a potentially effective strategy to enhance soil organic matter (SOM) stocks and thus the quality of soil and sustainability of arable cropping systems. We used the new soil-crop model USSF (Uppsala model of Soil Structure and Function) to investigate the potential for increasing SOM whilst maintaining or improving yields by modifying the root system of winter wheat in terms of below-ground allocation of carbon and key root traits. USSF combines physics-based descriptions of soil water flow, water uptake and transpiration by plants, with a simple (generic) crop growth model and a model of soil structure dynamics and soil organic matter turnover that considers the effects of soil physical protection and microbial priming. 

The USSF model was first calibrated against field data on soil water contents and both above-ground and root biomass of winter wheat measured during one growing season in a clay soil in Uppsala, Sweden. Based on five acceptable calibrated parameter sets, we created four model crops (ideotypes) by modifying root-related parameters to mimic winter wheat phenotypes with improved root traits. Long-term (30-year) simulations of a conventionally tilled monoculture of winter wheat were then performed to evaluate the potential effects of cultivating these ideotypes on soil water balance, soil organic matter stocks and grain yields.

Our results suggest that exploiting winter wheat varieties that allocate more assimilate to the root system would not in itself have any positive effect on soil organic matter storage and would also decrease grain yields. In contrast, deeper root systems or root systems that are more effective for water uptake were predicted to slightly increase grain yields, as well as increasing SOM stocks in the soil profile by ca. 3 to 5%. Combining all three improved root traits showed even more promising results: compared with the baseline “business-as-usual” scenario, SOM stocks in the soil profile were predicted to increase by ca. 7% in a 30-year perspective (as an average of the five parameter sets) without negatively impacting yields.

How to cite: Coucheney, E., Kätterer, T., Meurer, K., and Jarvis, N.:  Improving the sustainability of arable cropping systems by modifying root traits: a modelling study for winter wheat, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12359, https://doi.org/10.5194/egusphere-egu24-12359, 2024.

Root water uptake is a pivotal process in the regulation of water movement within the soil-plant-atmosphere continuum. At a specific atmospheric demand, root water uptake is determined by the architecture of the root system and the hydraulic properties of individual roots and root segments. In agricultural settings, root traits are affected by management practices, including breeding. Specifically for wheat, the most important European crop, a decrease in root system size has been observed in modern varieties compared to historical ones¹, and differences in root hydraulic properties between cultivated and wild species have been documented². However, an assessment on the long-term evolution of root hydraulic properties with breeding is still absent.  

Here, we investigated the effect of breeding on root hydraulic properties of wheat and its implications for root water uptake at the plant scale. For this, an experiment encompassing six wheat cultivars spanning over a century of breeding history was conducted. We measured the number of root axes (crown roots and seminal roots) of plants grown in the field during the tillering phase (BBCH <30) and the root hydraulic conductivity of young plants grown in hydroponics (<12 days, no crown roots), using the pressure chamber technique.

Average root hydraulic conductivity (per root surface area) did not differ among cultivars, but a pronounced decrease in the number of root axes was observed in the most recent cultivars. Based on these observations, simulations with the whole-plant 3-D model CPlantBox were performed, indicating a higher whole-root system conductance in the oldest cultivars at the end of the tillering phase, associated with a higher number of tillers and root axes. This suggests an evolution of wheat cultivars towards more conserving root water uptake strategies, a feature of special importance under water-limited conditions.

References 

• ¹Zhao et al. (2005). 10.1111/j.1744-7909.2005.00043.x
• ²Fradgley et al. (2020). 10.1007/s11104-020-04585-2 

How to cite: Baca Cabrera, J. C., Vanderborght, J., Behrend, D., Gaiser, T., Nguyen, T. H., Boursiac, Y., and Lobet, G.: Evolution of root hydraulic properties of wheat with breeding and its influence on root water uptake: insights from a field experiment and modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7991, https://doi.org/10.5194/egusphere-egu24-7991, 2024.

Soil moisture in forested regions displays considerable spatial and temporal variability within the soil-plant interaction. The high frequency of drying and wetting cycles exacerbates the uncertainty in this already complex relationship. Recent studies in forest hydrology have frequently postulated that soil physical properties and precipitation partitioning induce soil water content (SWC) variability. However, in-situ evidence for this linkage is scarce. To support the notion of SWC patterns corresponding to these two elements, a transect-based method was utilised. It clarifies the variation in soil moisture on a small scale and facilitates the identification of specific patterns with the distance from the tree stem. An intensive monitoring of SWC (52 profiles) and precipitation, including throughfall and stemflow, has been carried out in the near-natural beech forest in north-eastern Germany since 2022. It covers three study sites that are stocked over a terminal moraine and are classified as wet, intermediate and dry on the basis of the soil moisture gradient. The result stipulates increase of the SWC away from the stem during drying cycles at the dry study site. However, this appears to be the reverse for the wet site. During the wetting phase, soil moisture at intermediate and dry sites exhibited homogeneous variation, although the wet site experienced an increase in soil moisture by stem distance. Therefore, uncovering the distance from stem, root density distribution and canopy structure as possible controlling factors.  It is concluded, that within soil-plant interaction both soil physics and precipitation define the patterns of soil moisture variation during wetting cycles. Conversely, soil retention characteristics mainly anticipate water fluxes in the soil during drying periods.

How to cite: Azekenova, A., Feger, K.-H., and Julich, S.: What impacts the soil moisture dynamics in the near-natural beech forest?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-978, https://doi.org/10.5194/egusphere-egu24-978, 2024.

Rooting depth is critical for plants to acquire water and nutrient efficiently. However, when progressing deeper into the soil, a growing root must overcome physical obstacles such as stones and zones with different mechanical impedance (like hard pans and aggregates) which results in tortuous trajectories and a reduced ability to reach deeper soil horizons. We have developed different model systems which consists of roots growing in artificial substrates made of a customized arrays of stiff or deformable obstacles which the root can either bypass or penetrate based on the resistance of the obstacle. High-throughput imaging systems were used to capture time lapse data and image analysis techniques were used to track root responses to obstacles. In the presence of rigid obstacles, only a limited number of growth responses were observed with a transition from vertical to oblique trajectories observed as a function of size and distance between physical obstacles. When obstacles were deformable the likelihood of penetration could be predicted from factors such as the incidence angle, the length of the root that can bend freely, and the degree to which previous obstacles compress and anchor its base. Overall, our results showed that primary root growth in heterogeneous substrates is largely deterministic and can be predicted from the maximum curvature a root can bend, the spatial arrangements of obstacles and the mechanical stress anchoring the base of the root.

Keywords: root, soil, mechanical impedance, heterogeneity, biomechanics

How to cite: Yao, J., Barès, J., Kolb, E., and Dupuy, L.: The biomechanics of path of least resistance of roots in heterogeneous substrates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1452, https://doi.org/10.5194/egusphere-egu24-1452, 2024.

The SWAP model allows studying the behavior of agricultural systems at different spatial and temporal scales, addressing climate change adaptation and mitigation issues.

In recent years, it has been used in the viticultural sector to study the soil-plant-atmosphere (SPA) relationships in vineyards and to define and support the terroir concept and its resilience under climate change.

This contribution presents the results relating to the ability of the model to (i) shed light on the relationships between water stress and grape quality characteristics and (ii) evaluate the impact of climate change on the responses of the vineyard system of three vine varieties cultivated in southern Italy (Aglianico, Cabernet sauvignon and Greco).

In each case study, the calibrated and validated SWAP model output has been used to explore the relations between the plant water stress realized during the growing season and vine responses (physiological and productive responses). The identified relations were successively applied to evaluate the climate change (CC, RCP 4.5 and 8.5 ) adaptation of each vineyard system studied. Furthermore, in the case of the Aglianico grapevine, the evaluation of adaptation to CC was spatially extended to a region of southern Italy (Valle Telesina, BN; 20.000 ha) devoted to high-quality wine production, and the resilience of the terroir concept evaluated.

Finally, the strengths and limitations of SWAP application in the viticultural context will be discussed.

Keywords: grapevine, SPA system, terroir, climate change, vine water stress, grape quality.

How to cite: Bonfante, A.: SWAP model potentiality in the viticultural system study and analysis., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9239, https://doi.org/10.5194/egusphere-egu24-9239, 2024.

Understanding spatial variation in soil hydraulic properties is important for comprehending the physical behaviour of soil and for analysing field-scale water flow and solute transfer processes. Tension disc infiltrometers are commonly used for measuring in-situ unsaturated hydraulic properties of soil. In this study, spatial variation in soil hydraulic properties is analysed for an experimental plot at IIT Kanpur, India after harvest of rice crop using tension disc infiltrometer. Measurements were taken at three different depths of 10, 25 and 50 cm and at multiple locations in the field for consecutive supply pressure heads of -12, -9, -6 and -3 cm. The measured data was analysed using HYDRUS-2D model and four Maulem-van Genutchen parameters (θ_s, α, n and K_s) were inversely estimated. The maximum variation was observed in α at the depth of 50 cm. The reduced variability observed in pore size distribution index (n) could be attributed to the flooded irrigation practice in rice. The findings of this study enhance our understanding of soil-water interaction in agricultural settings.

Keywords: Soil hydraulic properties, Tension disc infiltrometer, HYDRUS-2D

How to cite: Vashishth, N., Dey, S., and Ojha, Dr. R.: Spatial variation in soil hydraulic properties in an agricultural field estimated using Tension Disc Infiltrometer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15793, https://doi.org/10.5194/egusphere-egu24-15793, 2024.

In a changing climate, grasslands are expected to experience major shifts in water supply and demand. To date, little is known about how projected future conditions of severe drought, climate warming, and rising CO₂ affect grassland water uptake, and whether adaptations of fine roots affect the capacity to extract water from soil. Using a multifactor global-change experiment in a managed montane C₃ grassland, we studied the individual and combined effects of drought, warming (+3 ℃), and elevated CO₂ (eCO₂; +300 ppm) on root water uptake (RWU) over three growing seasons. RWU was assessed across different layers of the main rooting horizon using diel soil moisture dynamics during non-rain periods. We also investigated treatment effects on fine roots (production, traits), fine-root-to-shoot ratios, and consequences for RWU capacity. By increasing vapour pressure deficit (VPD) and its effect on RWU rates normalized to soil water content (RWU_SWC), warming reduced RWU during hot periods. Under sustained warming, grassland decreased specific root length, and increased root diameters and fine-root-to-shoot ratios. Conversely, eCO₂ slowed RWU_SWC at high VPD, though fine-root adaptations were negligible. Compared to warming alone, future conditions (warming, eCO₂) increased RWU_SWC to a lesser extent and induced no fine-root adaptations, but reduced RWU to a similar degree. Drought reduced RWU (-66–75%) and increased water sourcing from deeper soil layers; however, a hot season amplified any RWU reductions under future conditions by 20%. Altogether, our study demonstrates that (i) RWU in C₃ grasslands declines in a warmer, drier future, though (ii) eCO₂ will mitigate the need for fine-root adaptations, maintaining RWU capacity. However, (iii) rising temperatures will exacerbate RWU reductions under drought. Therefore, hot droughts should have significant repercussions for water dynamics in C₃ grasslands.

How to cite: Tissink, M., Radolinski, J., Reinthaler, D., Venier, S., Pötsch, E. M., Schaumberger, A., and Bahn, M.: Individual versus combined effects of drought, warming and eCO2 on grassland water uptake and fine roots, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3773, https://doi.org/10.5194/egusphere-egu24-3773, 2024.

The upscaling of hydrologic processes at catchment scale from small scale soil hydraulic parameterization has been met with limited success. For example, spatially variable attributes (topography, surface properties, preferential flow paths) affect infiltration and runoff rates, introducing uncertainties that mask the role of soil properties at catchment scales. In contrast, evidence suggests that evapotranspiration (ET) remains controlled by small scale processes (flow of water to roots, capillary pumping to drying surface) that are critically dependent on soil hydraulic properties. This scale invariance of ET offers opportunities for upscaling emergent ecosystem scale ET dynamics from basic soil information.

ET switches from being energy to water limited at a critical soil water threshold when the water flow through the soil matrix can no longer sustain the atmospheric water demand. This transition depends on the soil water characteristics and soil hydraulic conductivity curve (characterized by their nonlinearity and dependence on soil texture), on plant traits (root length density, leaf area, and xylem vulnerability), and on atmospheric conditions (e.g., vapor pressure deficit and wind velocity). Despite the importance of plant hydraulic traits and atmospheric conditions, the large variations in soil hydraulic properties as a function of soil texture, make small scale hydraulic properties the key in controlling ET during soil drying (Lehmann et al. 2008, Carminati and Javaux 2020). It follows that soil moisture thresholds of ET are controlled by water flow in soils and by the soil hydraulic conductivity. Accordingly, small-scale models of water flow to the soil surface and to the roots successfully predict soil moisture thresholds that have been measured at the ecosystem scale.

The question of why upscaling flow equations and properties derived from small sample and single plants to ecosystems proved to be successful is an important one. In contrast to water infiltration and run-off affected by the scale-dependent size of surface heterogeneities, the spatial scale of water flow from soils to roots does not increase with the scale of observation. It is the limiting flow through the soil matrix, with spatial scales of 0.01-0.1 m, which sets the point when plants downregulate transpiration and photosynthesis as the soil dries; a process that is similar to the evaporation from the soil surface.

In conclusion, despite the challenges and uncertainties in applying soil physical laws to larger scale, the application of Buckingham-Darcy law to properly predict matrix flow and evapotranspiration at the ecosystem scale is doable and relevant for understanding drought effects on ecosystem water use and productivity.

Carminati A, Javaux M. Soil rather than xylem vulnerability controls stomatal response to drought. Trends in Plant Science. 2020 Sep 1;25(9):868-80.

Lehmann P, Assouline S, Or D. Characteristic lengths affecting evaporative drying of porous media. Physical Review E. 2008 May 16;77(5):056309.

How to cite: Carminati, A., Wankmüller, F., Delval, L., Baur, M. J., Javaux, M., Wolf, S., Lehmann, P., and Or, D.: Ecosystem scale evapotranspiration is controlled by small scale processes and soil hydraulic properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11972, https://doi.org/10.5194/egusphere-egu24-11972, 2024.

Given the critical role of tropical forests in providing ecosystem services, extensive global efforts have been made to conserve and restore these vital areas. Despite the recognized environmental value of preserved forests, substantial uncertainties persist regarding the impact of reforestation activities on water recharge. While some studies suggest that reforestation might lead to a reduction in surface and groundwater reserves, other research, backed by public opinion, indicates that forest recovery enhances water reserve.

Recognizing this as a crucial scientific and environmental management concern, our study aims to explore the role of de and reforestation on soil hydraulic properties. Combining in situ monitoring of water status and soil physical properties, our study aimed at addressing the following scientific question: how does soil structure evolve with different revegetation stages?

We selected several plots along a hillslope transect in the oceanic forest (Sao, Paulo, Brasil), with different reforestation stages (40 y.o. forest vs deforested pasture).  Deep percolation measurements were conducted using sealed bottom lysimeters. A comparative analysis of soil conditions in contrasted study areas involved soil physical properties such as texture, permeability, and bulk density, along with assessing the seasonal variability of matric potential and soil moisture content.

Our findings reveal that soil infiltration capacity of pasture was lower than under a 40 yr-old forest. We also observed that soil macroporosity  was higher under the forest area than  under the pasture area, potentially influencing infiltration rates and favoring deep drainage in the forest compared to the pasture.

How to cite: Borma, L., Sakagushi, F., Demetrio, W., Pupin, B., Ventura, D., Meneghetti, C. D., Devoie, B., Dermauw, C., Parmentier, L., and Javaux, M.: Tropical humid forests: water consumers or producers? The case of a forest fragment in the Atlantic Forest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16651, https://doi.org/10.5194/egusphere-egu24-16651, 2024.

Grasslands are highly dynamic ecosystems that adapt to environmental drivers such as climate, soil properties and anthropogenic management. However, the belowground response and adaptation of grassland communities to environmental drivers are poorly understood. Here, we investigate differences in the temporal dynamics of root water uptake, its depth pattern and the evolution of plant-available soil water storage between three different grassland management types and in two different climate treatments (control and future). The climate scenarios included treatments with and without a precipitation manipulation that partially shifts the precipitation from summer to spring and autumn. Soil moisture measurements were carried out at 6 depths up to 90 cm on three land use types (i) extensively and (ii) intensively managed grassland and (iii) extensive pasture at the Global Change Experimental Facility (GCEF) in Central Germany. Afterwards, root water uptake was estimated from diurnal variations in soil water content. We found that the grassland vegetation, in general, extracts water to depths of up to 90 cm during the growing season and can go even deeper. Extensively managed grasslands in the future climate scenario had increased root water uptake depths even in spring when water was not limiting indicating an adaptation to changing rainfall patterns. In contrast, more intensively managed grasslands could not compensate for greater water limitation with deeper root water uptake. Root water uptake depths during summer differed between the management types only in the future climate scenario, with drier conditions, along with the management intensity: The more intense, the shallower the uptake. This demonstrates that the ability to adapt to changing climate depends on management. Cumulative atmospheric water deficit was the main driver of root water uptake depth until the first mowing while ecosystem structure (vegetation height) and soil properties (plant available water at the beginning of the vegetation period) affect that relationship.

How to cite: Westermann, S., Bumberger, J., Schädler, M., Thober, S., and Hildebrandt, A.: How grasslands are managed will determine their ability to adapt to increased water scarcity under climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17711, https://doi.org/10.5194/egusphere-egu24-17711, 2024.

Plant nutrient foraging depends on roots and mycorrhizal fungi, which are affected by plant carbon (C) investment and soil nutrient availability. The C supply for root metabolism and associated fungi might be diminished as the host plant size increases, while the quality and quantity of soil nitrogen (N) change with forest succession. There is still no holistic understanding of how the organization of belowground mycorrhizal root structure and fungi in the nutrient acquisition continuum shifts with forest age and soil resources, which restrains our understanding of the functional relations among roots, fungi, and soil. Here we examined the shifts in the absorptive root and mycorrhizal strategies, and changes in soil-associated fungal community compositions along a temperate larch forest chronosequence nested with a long-term N fertilization gradient. We found that the effect of forest age outweighed soil N addition in our forest. As tree age increased, root respiration and specific root length decreased, but protective investments such as tissue density and phenolics decreased. Meanwhile, the proportion of ectomycorrhizal fungi with a short-distance exploration type increased, but those with a long-distance exploration type decreased. The shifts in root and mycorrhizal fungal traits demonstrate a nutrient acquisition continuum from "young explorative roots with long mycorrhizas" to "mature conservative roots with short mycorrhizas". A trade-off between the root architecture and root segment metabolism, and a complementarity between the size of the root system and mycorrhizal exploration types functionally constrains this nutrient acquisition continuum. Our results thus suggested forest succession drives the covariations among root system size, root metabolic rate, mycorrhizal fungal exploration type, and soil-associated fungal functional groups.

How to cite: Ma, Z., Ding, G., Zeng, W., Yan, T., and Sun, L.: Forest succession drives systematic change of root-mycorrhizal foraging strategies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22231, https://doi.org/10.5194/egusphere-egu24-22231, 2024.

Soil moisture plays a key role in the hydrological cycle by partitioning of precipitation between evapotranspiration and deep infiltration. The ongoing climate change is causing an increase in air temperatures, changes in precipitation patterns and decrease in winter snow cover. It simultaneously shifts spring snowmelt towards winter months. Both air temperature and precipitation patterns are suspected to be one of the influential factors affecting changes in soil hydraulic properties. Thus, the ongoing climate change can alter soil hydraulic properties, commonly considered time-invariant, and the prediction of future soil moisture regime can therefore be more uncertain than originally thought.

We measured a saturated hydraulic conductivity using an automatic single-ring infiltrometer thorough one entire year in a monthly time-step in the spruce covered site. Higher infiltration rates were regularly observed in the middle of a vegetation season compared to lower rates observed in a dormant season. Based on this finding we implemented a new function, enabling the seasonal variation of the saturated hydraulic conductivity, into the simple bucket-type soil moisture model. The root-mean square error of soil moisture prediction decreased by one-third and Nash-Sutcliffe efficiency increased significantly indicating possible benefits of a new concept. Main reasons behind the seasonal variability of soil hydraulic properties in uncultivated sites can be numerous (encompassing biological activity, changes in the root architecture, wetting/drying and freezing/thawing cycles altering the pore space) and deserve further investigation.

The major outcome is represented by the concept enabling a more efficient prediction of soil moisture regime outside the vegetation season, which is increasingly more important as the onset of soil drought can often be observed at the end of the dormant season. Furthermore, modelling of a climate change impact on the availability of water resources will also benefit from a better prediction of the soil moisture by considering regular structural changes of soil.

How to cite: Šípek, V., Vlček, L., Hnilica, J., and Tesař, M.: Modelling of soil water regime in forested areas: potential benefits of seasonally variable soil hydraulic properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20215, https://doi.org/10.5194/egusphere-egu24-20215, 2024.

Above-ground plant litter decomposition has a major influence on the global carbon (C) cycle by transferring 50% of net primary productivity to soil organic matter and releasing 60 Pg C annually into the atmosphere. Despite extensive research devoted to disentangling the main drivers controlling litter decomposition, the role of lithology remains understudied. Here, two studies were conducted to investigate the combined effects of lithology and climate on needle litter decomposition on three distinctive lithological substrates (calcareous, peridotite, and metapelite) along a precipitation gradient (ranging from 641 to 1097 mm yr^-1) in the province of Málaga, south of Spain.

Study one examined needle litter decomposition of Pinus pinaster (maritime pine) along the experimental gradient, and study two was a reciprocal transplant experiment established on calcareous and peridotite lithological substrates located in the centre of the precipitation gradient with litter of contrasting chemical recalcitrance obtained from P. pinaster and Abies pinsapo (Spanish fir) to assess the impact of lithology on the home field advantage hypothesis.

Total litter mass loss during decomposition was highest in the calcareous substrate, exceeding metapelite and peridotite substrates by 24% and 50%, respectively. Decreased precipitation reduced litter mass loss only in calcareous soils (35%) but had little effect on metapelitic and peridotite sites indicating that more productive bedrock types are influenced to a greater degree by reducing precipitation, supporting the boom-bust hypothesis. On peridotite substrates, decomposition of the labile soluble cell fraction and cellulose-based crude fibre fractions of intermediate recalcitrance was delayed by one dry season whereas lignin decomposition ensued immediately highlighting physicochemistry-induced modification of substrate accessibility.  Moreover, study two demonstrated a pronounced home-field advantage for litter on calcareous substrates, contrasting with an away-field advantage for litter derived from peridotite substrates. These results underscore the significant role of lithology in dictating litter decomposition dynamics, directly influencing both litter quality and microbial substrate accessibility.

Given that lithology directly impacts litter quality and its response to changing precipitation patterns—both critical variables in global ecosystem carbon models—incorporating lithological factors is essential for accurately predicting how plant litter decomposition will respond to climate change.

How to cite: Fishburn, D., Smith, A., Markesteijn, L., and Rey, A.: The effect of lithology on leaf litter decomposition of Pinus pinaster forests along a Mediterranean precipitation gradient, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11051, https://doi.org/10.5194/egusphere-egu24-11051, 2024.

Root water uptake strongly affects soil water balance and plant development. It can be described by mechanistic models of soil-root hydraulics based on soil water content, soil and root hydraulic properties, and the dynamic development of the root architecture. Recently, novel upscaling methods have emerged (Vanderborght et al. 2023, 2021), which enable the application of detailed mechanistic models on a larger scale, particularly for land surface and crop models, by using mathematical upscaling.

In this study, we explore the underlying assumptions and the mathematical fundamentals of the upscaling approach. Our analysis rigorously investigates the errors introduced in each step during the transition from fine-scale mechanistic models, which considers the nonlinear perirhizal resistance around each root, to more macroscopic representations. Upscaling steps simplify the representation of the root architecture, the perirhizal geometry, and the soil spatial dimension and thus introduces errors compared to the full complex 3D simulations. In order to investigate the extent of these errors, we perform simulation case studies: spring barley as a representative non-row crop and maize as a representative row crop, and using three different soils.

We show that the accuracy of the upscaled modeling approach strongly differs, depending on  root architecture and soil type. Furthermore, we identify the individual steps and assumptions that lead to the most important losses in accuracy. An analysis of the trade off between model complexity and accuracy provides valuable guidance for selecting the most suitable approach for specific applications.

References 

Vanderborght, J., Couvreur, V., Meunier, F., Schnepf, A., Vereecken, H., Bouda, M., and Javaux, M. (2021). From hydraulic root architecture models to macroscopic representations of root hydraulics in soil water flow and land surface models. Hydrology and Earth System Sciences, 25(9):4835–4860.

Vanderborght, J., Leitner, D., Schnepf, A., Couvreur, V., Vereecken, H., and Javaux, M. (2023). Combining root and soil hydraulics in macroscopic representations of root water uptake. Vadose Zone Journal, e20273.

How to cite: Leitner, D., Schnepf, A., and Vanderborght, J.: From hydraulic root architecture models to efficient macroscopic sink terms , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7315, https://doi.org/10.5194/egusphere-egu24-7315, 2024.

To assess the impact of agricultural practices on water and carbon cycles within specific Genome-Environment-Management combinations, understanding the interactions across the Soil-Plant-Atmosphere continuum (SPAC) is crucial.

Indeed, soil water conditions influence carbon concentration and transport, impacting soil carbon physical and biochemical reactions.

The soil water and carbon status affect, in turn, the plant water and carbon dynamics directly via the plant-to-soil water or carbon gradient, and indirectly via plant water status, influencing its inner balance of water (uptake, transpiration and flow) and carbon (assimilation, usage for maintenance and growth, storage, respiration, rhizodeposition, and transport).

Reciprocally, plant water and carbon balances affect the soil carbon cycle in the short term through root water uptake and rhizodeposition. Those rhizodeposits are, for the most part, made of exudates and mucilage. Root exudates are low molecular weight organic compounds that are mainly passively diffused, while mucilage is a fluid made of polymers with high molecular weight created from starch via an active process.

Modelling plant and soil water and carbon processes, along with their interactions, can help to understand better and represent the effects of the underlying feedback loops. In this study, we therefore coupled the Functional Structural Plant Model (FSPM) CPlantBox with the rhizosphere model TraiRhizo, implemented using the porous medium flow and transport solver DuMu^x.

The overall coupled model and multiscale framework includes a module of 3D plant architecture development, and modules to represent flow and transport within the plant, the soil and the perirhizal zone around each root segment. Flows between compartments are solved implicitly via fixed-point iteration, using parallel computation for both the 3D soil and rhizosphere models.

We present a case study in which we simulated the growth of a C3 monocot and observed how changes in soil water content, due to root water uptake, influenced dissolved carbon concentration and (de)activation of the soil microbial communities during a dry spell.

In the future, the model will be applied to assess the impact of small dry spells at various stages of plant development against a baseline scenario. In time, this model could support plant breeding efforts to find root traits that aim for more drought-resistant plants in specific pedoclimatic environments.

How to cite: Giraud, M., Sircan, A., Lobet, G., Streck, T., Leitner, D., Pagel, H., and Schnepf, A.: Coupling a Functional-Structural Plant Model with a Rhizosphere Model To Gain Multiscale Insights into Plant-Soil-Atmosphere Interactions for Water and Carbon Cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17850, https://doi.org/10.5194/egusphere-egu24-17850, 2024.

Vegetation plays a crucial role in regulating the water cycle through transpiration, which is the water flux from the subsurface to the atmosphere via vegetation roots. The amount and timing of transpiration is controlled by the interplay of seasonal energy and water supply. The latter strongly depends on the size of the root zone storage capacity (S_r) which represents the maximum accessible volume of water that vegetation can use for transpiration. S_r is primarily influenced by hydro-climatic conditions as vegetation optimizes its root system in a way it can guarantee water uptake and overcome dry periods. S_r estimates are commonly derived from root zone water deficits that result from the phase shift between the seasonal signals of root zone water inflow (i.e., precipitation) and outflow (i.e., evaporation). In irrigated croplands, irrigation water serves as an additional input into the root zone. However, this aspect has been ignored in many studies, and the extent to which irrigation influences S_r estimates was never comprehensively quantified. In this study, our objective is to quantify the influence of irrigation on S_r and identify the regional differences therein. To this aim, we integrated two irrigation methods, based on irrigation water use and irrigated area fractions, respectively, into the S_r estimation. We evaluated the effects in comparison to S_r estimates that do not consider irrigation for a sample of 4511 catchments globally with varying degrees of irrigation activities. Our results show that S_r consistently decreased when considering irrigation with a larger effect in catchments with a larger irrigated area. For catchments with an irrigated area fraction exceeding 10%, the median decrease of S_r was 17 mm and 22 mm for the two methods, corresponding to 12% and 17%, respectively. S_r decreased the most for catchments in tropical climates. However, the relative decrease was the largest in catchments in temperate climates. Our results demonstrate, for the first time, that irrigation has a considerable influence on S_r estimates over irrigated croplands. This effect is as strong as the effects of snow melt that were previously documented in catchments that have a considerable amount of precipitation falling as snow.

A manuscript associated with this abstract is available as preprint:

van Oorschot, F., van der Ent, R. J., Alessandri, A., and Hrachowitz, M.: Influence of irrigation on root zone storage capacity estimation, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2622, 2023.

How to cite: van der Ent, R., van Oorschot, F., Alessandri, A., and Hrachowitz, M.: The influence of irrigation on root zone storage capacity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15520, https://doi.org/10.5194/egusphere-egu24-15520, 2024.

Climate change will exacerbate drought events in many regions, increasing the demand on freshwater resources and creating major challenges for viticulture. The knowledge on grapevine drought stress physiology has increased significantly in recent years, but a holistic comprehension on how soil-grapevine hydraulic conductances develop and are regulated in the soil-grapevine-atmosphere continuum (SPAC) remains poorly understood. In particular, how soil type affects the grapevine hydraulic response to drought is still an open question.

The aim of this work is to understand how the hydraulic conductances in the SPAC continuously evolve according to soil type, during drought.

The continuous, concomitant and automatic monitoring of soil and collar water potentials, as well as sap flow, made it possible to characterize the evolution of the soil-grapevine hydraulics in situ in real-time. To investigate the impact of the soil type, two vineyards planted with Vitis vinifera cv. Chardonnay were selected due to their intra-field heterogeneity of soil properties (two subplots per vineyard). In a first vineyard, soil-grapevine hydraulics were measured on a sandy subplot and on a loamy subplot. In a second vineyard, we worked on a loamy subplot and on a silty-clay subplot.

We found that grapevine hydraulic response to soil drying is soil texture specific. Stomatal closure was observed for grapevines planted on coarse-textured soils, but not, or little, on fine-textured soils. This stomatal response was triggered by a decrease in belowground hydraulic conductance and not xylem cavitation in the trunk. This suggests that the interaction between the grapevine and the soil hydraulic environment plays a crucial role in shaping hydraulic behaviour of Chardonnay during drought periods.

While soil dries out, the decline in soil hydraulic conductivity led to a steep and nonlinear reduction in soil matric potential at the soil-root interface, with greater reduction in sandy soils compared to loamy soils. This rapid decline in soil hydraulic conductivity implies that the soil is more rapidly limiting (at less negative soil water potential), triggering earlier stomatal closure in coarse-textured soils. Stomatal regulation is amplified in sandy profile as compared to fine textured profile within the same grape variety.

How to cite: Delval, L. and Javaux, M.: In situ grapevine hydraulic response to drought is soil-texture specific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15318, https://doi.org/10.5194/egusphere-egu24-15318, 2024.

Desertification is one of the most important environmental problems in the world. In arid and semi-arid regions, desert shrub reconstruction is one of the most effective ways to prevent desertification and promote ecological restoration. Recently, many studies have reported the hydraulic trade-off, coordination, and hydraulic segmentation of woody plants, however, the mechanism of how the hydraulic segmentation drives morphological adjustment of desert shrub to response to drought is still largely unclear. Here, the two-year-old seedlings of Caragana korshinskii and Artemisia ordosica as materials were subjected to continuous drought treatment. The aim is to explore hydraulic strategies and quantify the hydraulic threshold when morphological adjustments drive occurs. The results showed that tissues water content of C. korshinskii and A. ordosica under persistent drought showed an exponential decrease with the decrease of soil water content, but it is with a certain lag effect. Meanwhile, the leaf water potential, xylem specific hydraulic conductivity, degree of natural embolism and photosynthetic rate, etc. showed decrease trend with persistent drought. Above results suggested that hydraulic functional traits were drove by changes of soil water, but the tissue hydraulic capacitance acts as a buffer against decline of above traits. Moreover, the water potential thresholds of 88% stomatal closure and hydraulic safety margin in C. korshinskii was significant high than A. ordosica’s, which indicated that C. korshinskii are more vulnerable to drought. Then, the morphological adjustments such as leaf wilting and lateral branches wilting further occurred with the continued drought, however, the lateral branches of C.korshinskii could germinate again after soil water recovery, but A.ordosica could not. Overall, the water potential and hydraulic conductivity threshold for morphological adjustment of desert shrub such as leaves wilting and lateral branches wilting under continuous drought were quantified and the hydraulic strategies were elucidated that was regulated by hydraulic segmentation.

How to cite: Huo, J. and Zhang, Z.: Hydraulic strategies of desert shrubs responding to morphological adjustment under persistent drought, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14434, https://doi.org/10.5194/egusphere-egu24-14434, 2024.