Displays

Root systems show a tremendous diversity both between and within species, suggesting a large variability in plant functioning and effects on ecosystem properties and processes. In recent decades, developments in many areas of root research have brought considerable advances in our understanding of root traits and their contribution to plant and ecosystem functioning. However, despite major progress, a comprehensive overview—bridging research fields—is lacking. Furthermore, considerable uncertainties exist in the identification of root entities, and the selection and standardized measurement of traits. Here, we provide a comprehensive overview on root entities, exemplify recent advances in our understanding of both theoretical and demonstrated relationships between root traits and plant or ecosystem functioning, discuss trait-trait relationships and hierarchies among traits, and critically assess current strengths and gaps in our knowledge.

How to cite: Rewald, B., Freschet, G. T., Roumet, C., Stokes, A., Weemstra, M., Bardgett, R. D., Bengough, A. G., Comas, L. H., De Deyn, G. B., Johnson, D., Klimešová, J., Lukac, M., McCormack, M. L., Meier, I. C., Pagès, L., Poorter, H., Prieto, I., Wurzburger, N., and Zadworny, M.: Root traits as key proxies to unravel plant and ecosystem functioning: entities, trait selection and outlook, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20261, https://doi.org/10.5194/egusphere-egu2020-20261, 2020.

Drought is considered a severe natural risk that increases drying-rewetting frequencies of soil. Yet, it remains largely unknown how forest ecosystems respond, hampering our ability to evaluate the overall sink and source functionality for this large carbon pool. Recent investigations present that the loss of soluble carbon via root exudation increases under drought, facilitating fundamental carbon stabilization and mineralization dynamics. However, information on the vertical variation of root exudation from interacting tree species is missing. Here we show that drought increases root exudation rates only in the upper soil profile, while exudation rates decrease in the deeper profile under drought. These trends occurred in both, monocultures and species mixtures. Surprisingly, beech (Fagus sylvatica) and spruce (Picea abies) trees showed opposing results depending on species mixture. While root exudation rates increased in beech growing together with spruce, drought-susceptible spruce had higher exudation rates when grown in monoculture, suggesting the benefit of spruce in mixed cultures via reduced belowground carbon loss. Our results demonstrate that stimulation of root exudation rates with drought exists in natural temperate forest ecosystems, but only in shallow soil depths. In contrast, decreased exudation rates in deeper soil during drought suggest carbon stabilization. The exudate composition can help to determine how priming of soil organic matter relates to microbial respiration and to disclose belowground processes of complementary species interaction.

How to cite: Brunn, M., Hafner, B. D., Jungkunst, H. F., and Bauerle, T. L.: Tree species interaction and soil depth affect the response of root exudates to drought, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9791, https://doi.org/10.5194/egusphere-egu2020-9791, 2020.

Sustainably intensifying global crop production in a world of diminishing natural resources is paramount for the attainment of zero hunger worldwide (a United Nations sustainable development goal). Key to this sustainable intensification is a deep understanding of the dynamics and complexities of plant-soil interactions for optimisation of plant productivity. Neutron computed radiography and tomography are powerful, non-invasive tools that enable the characterisation of plant-soil systems in situ. They also enable the visualisation and quantification of water distribution and movement within plant-soils systems. In this novel study, we use high resolution neutron computed tomography to investigate root system architectural differences in two different genotypes (Wild type vs TaEPF1-OE1-water use efficient mutant line) of bread wheat (Triticum aestivum). We further investigated how wheat roots interact with the heterogeneously distributed soil moisture. For this investigation, plants were grown in an aggregated sandy loamy soil with moderate amounts of organic matter (4%) for 13 days prior to imaging. We were able to produce a detailed three dimensional visualisation of the root architectural distribution of the two different genotypes imaged. These did not show significant differences between the two genotypes under investigation. We were also able to visualise relative soil moisture distribution and made inferences to how the roots of the wheat plants under investigation interact with the heterogeneously distributed soil moisture. Our results showed increased lateral root growth in regions with finer soil aggregates that had an estimated lower moisture content as compared to larger soil aggregates that retained higher amounts of moisture. This study demonstrates that detailed investigations into plant-soil interactions using neutron imaging techniques can be done successfully even in aggregated soils with considerable amounts of organic matter. This is a departure from the majority of neutron imaging experiments that predominantly use disaggregated sand soils devoid of organic matter as a growth medium.

How to cite: Mawodza, T., Menon, M., Casson, S., and Burca, G.: Visualisation and quantification of wheat root system architecture and soil moisture distribution in an aggregated soil using neutron computed tomography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1196, https://doi.org/10.5194/egusphere-egu2020-1196, 2020.

The first Nc dilution curve was based on dry matter (DM) power function. This model is limited to  point of singularity near zero. Another disadvantage was that it required meaasurements of DM which is time and labor consuming. Alternatively we proposed a logistic model that starts at zero and on the abscissa assumed a linear relationship between days after emergence (DAE) and DM throughout the relevant stages of wheat growth cycle.  

The Objectives of this study were to: 1) To demonstrate the feasibility of digital camera to replace laboratory tests. 2) To Determine critical N (Nc) and Nitrogen nutrition Index(NNI) of spring wheat and 3) Use N% and dry matter yield in order to calculate N uptake by wheat. This last is expected to be a tool to calculate the required amount of nitrogen to obtain maximum yield.

Wheat experiments were conducted in greenhouse lysimeters. Varied rates of N fertilizer (equivalent to 0–180 kg ha^-1) and several  cultivars varying from shortest to longest ripening growth period. Nc reduced gradually from about 6% to 2%  ( =60-20 gr/Kg) when DM increased with DAE  from 0 to 14,000 kg/ha during 80 growing days.  NNI was stable and clearly distinct between   maximal index (1.0  and minimal index (0.2) when (DAE) was about 60;   Photographs succeeded to replicate laboratory measurements and obtained a linear regression curve with a unity  slop and r²=0.93. Nitrogen.  use efficiency (NUE) ranged from 50 to 65 kg  DM/unit N and from 30 to 50 Kg grain /unit N .

How to cite: Ben-Asher, J.: Using simple RGB Camera to estimate Nitrogen Uptake, Nitrogen Nutrition Index (NNI) and critical Nitrogen: Spring wheat case study., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5769, https://doi.org/10.5194/egusphere-egu2020-5769, 2020.

It is known that measuring and modeling of water and solute fluxes across soil-plant-atmosphere is nowadays a very important challenge because of the complexity of both soil and plants. In particular evapotranspiration (Schymanski and Or, 2017) is related with radiation, temperature, relative humidity, wind but it depends also by the water content in soil. Specifically, the water content varies with precipitation and with the water properties of soil, soil water retention curves and soil hydraulic conductivity.  
To consider the effects of water content on the rate of evapotranspiration it is necessary to study infiltration and evapotranspiration processes and find a physical, but also, a modelling point of view to coupled these processes.  

Considering the 1D problem we implement a virtual lysimeter model in which we coupled infiltration and evapotranspiration by using stress factor (Collatz at all, 1991), with which we can compute effective evapotranspiration and remove it from Richards’ equation balance (Casulli and Zanolli, 2010). In addition, the modeling of water and solute fluxes across soil-plant-atmosphere is made possible by implementation of travel times of waters within vegetation, the growing of the roots and in general the growing of the plants. 

Casulli e Zanolli, 2010. A Nested Newton-type algorithm for finite volume methods solving Richards’ equation in mixed form. SIAM J. SCI. COMPUT. Vol. 32, No. 4, pp. 2255–2273.

G. James Collatz, J. Timothy Ball, Cyril Grivet and Joseph A. Berry, 1991. Physiological and environmental regulation of stomatal conductance, photosynthesis and transpiration: a model that includes a laminar boundary layer. Agricultural and Forest Meteorology, Vol. 54, pp. 107-136.

P.M. Cox, C. Huntingford, R.J. Harding, 1998. A canopy conductance and photosynthesis model for use in a GCM land surface scheme. Journal of Hydrology 212–213, 79–94.

Jarvis, P.G., 1976. The interpretation of the variances in leaf water potential and stomatal conductance found in canopies in the field. Phil. Trans. Roy. Soc. Lond. B273, 593–610.

Stanislaus J. Schymanski and Dani Or, 2017. Leaf-scale experiments reveal an important omission in the Penman–Monteith equation. Hydrol. Earth Syst. Sci., 21, 685–706.

How to cite: D'Amato, C., Tubini, N., Bottazzi, M., Noto, L., and Rigon, R.: Hydrology of plants: Modeling the interaction between infiltration and evapotranspiration., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6033, https://doi.org/10.5194/egusphere-egu2020-6033, 2020.

The Klyazma river catchment basin is located in the center of the East European plain. It is characterized by a diverse landscape structure but at the same time represents a single ecosystem possessing common functioning features and similar features of dynamic processes.

The biological indicators dynamics of the Klyazma river basin landscape functioning has been analyzed. These indicators included: phytoproductivity, photosynthetic activity, soil cover carbon accumulation, as well as the analysis of land use structure changes over the past 20 years.  The assessment was carried out for the entire basin, as well as for individual landscapes within the basin differing in structure and composition of the soil and vegetation cover.

The research was performed using geoinformation analysis of remote sensing data and cartographic information applying basin approach. The river network vectorization and the watershed boundaries definition were carried out basing on digital terrain model (DEM). The input data comprised radar topographic survey of the Earth-SRTM 90. The productivity indicators calculation in carbon units, LAI (Leaf area index) and FPAR (Fraction of Absorbed Photosynthetically Active Radiation) indices are based on Modis data. Organic carbon stocks in soil are determined using the "Trends. Earth " GIS package QGIS 2.18.

The land use structure analysis shows that the trend for forest vegetation increase and arable land and pastures reduction is common to all landscapes, but different in changes speed and scale. The most stable is the land structure in Meshchera province, where almost 90% is occupied by forests and their area has not changed significantly.

Over the period of 2000 - 2019, the Klyazma river basin ecosystem was characterized by the annual value fluctuations of gross primary GPP production, net primary NPP production, and MP respiration costs up and down in comparison with the average values. There is no stable tendency in productivity growth or decline.

The maximum annual changes in productivity indicators are observed for the landscape of the Klin-Dmitrov ridge. The analysis showed that various landscapes differ in their biological parameters varying within different limits.

The agricultural land overgrowing with forest vegetation is accompanied by the increase in carbon deposition in the soil. Landscapes of the stable land use structure are characterized with zero carbon balance, while landscapes with forest vegetation with slightly negative carbon balance in the soil. However, the average biological indicators of the entire river basin ecosystem remain relatively stable. It testifies of the compensating biological mechanisms maintaining the ecosystem stability within a large ecosystem. That is, changes in some landscapes are compensated by changes in others according to the feedback principle.

The analysis of productivity features, land use structure, and carbon deposition in the soil in the Klyazma basin and certain key sites associated with different landscapes allowed us to determine a representative key site, located within Klin-Dmitrov ridge for the environmental monitoring of the entire basin.

The research allowed determining a representative area within the basin for environmental monitoring of the entire basin ecosystem.

The research has been carried out under RFBR financial support (№ 19-05-00363)

How to cite: Trifonova, T., Mishchenko, N., and Shutov, P.: Soil and vegetation cover spatial-temporal dynamics of the river basin landscapes according to the remote sensing data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9695, https://doi.org/10.5194/egusphere-egu2020-9695, 2020.

The use of microorganisms for improving plant performance under limiting conditions can be traced throughout history. Interestingly the first commercial biological plant growth promotor was patented in 1896. However, the understanding how the organisms interact on molecular level really took off after the advent of the genomic era which produced the tools needed for understanding how plants and microorganisms modulate each-other’s gene expression and metabolism. Today more than ever, the holistic understanding of plant nutrient uptake and novel strategies to improve nutrient uptake are of utmost importance. Our work focuses on nitrogen (N) – the second most abundant nutrient in plants and phosphorus (P) – a finite global resource. We present studies where use of plant growth promoting rhizobacteria (PGPR) resulted in improved plant performance under limited N or P in Brachypodium - a model plant for cereals. Plant roots were analyzed with the non-invasive root phenotyping platform GrowScreen Page [1], or with the 3D printed EcoFab microcosms [2]. The latter was adapted and used in combination with Plant Screen Mobile [3], for non-invasive shoot area estimation, in conjunction with root scanning, over time. On the other hand, the performance of barley plants under the influence of 2 fungal interaction partners were investigated in soil system, using magnetic resonance imaging [4].

The plant response to a micro-organism is largely dependent on the surrounding conditions. Examples of plants treated with plant growth promoting rhizobacteria (PGPR) and grown under high and low N show that: the plant phenotype, N content within the plant and molecular response vary depending on the N availability in the surrounding medium.

Furthermore, we were able to dissect the plant phenotype of plants grown under limiting P in soil-less medium, and found that plant biomass was higher in plants inoculated with PGPR. A time series image-analysis of root phenotype showed the changes in root architecture, pin-pointing the time-window when growth promotion took effect after inoculation. A sand experiment confirmed these results.

Finally, the interaction between Barley roots and two fungi (a pathogen and a putative beneficial partner) was investigated to find dynamic response in root growth in soil that varied in soil depth, and had a different progression through time based on treatment.

We argue that for successful use of PGPR in context of nutrient uptake we need to account for: time in context of plant developmental stage [5] and moment of application, the organisms in question and the surrounding condition. Efforts are needed to elucidate the proper interaction partners and application points to result in a sustainable solution for agriculture.

1. Funct Plant Biol, 2017. 44(1)
2. New Phytol. 2019; 222(2): 1149–1160
3. Plant Methods 2019 15:2
4. Plant Physiol 170(3): 1176-1188.
5. New Phytol. 2019 doi: 10.1111/nph.15955

How to cite: Arsova, B., Sanow, S., Schillaci, M., Kuang, W., Huesgen, P., Sarkar, D., Zuccaro, A., Roessner, U., and Watt, M.: From the root’s point of view: understanding the plant response to beneficial microbes, with primary aim of improved plant nutrient uptake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20041, https://doi.org/10.5194/egusphere-egu2020-20041, 2020.

Although 40% of total terrestrial precipitation transits the rhizosphere, there is still substantive lack of understanding of the rhizosphere biophysical properties and their impact on root water uptake. Our hypothesis is that roots are capable of altering the biophysical properties of the rhizosphere and hereby facilitating root water uptake. In particular, we expect that root hairs maintain the hydraulic contact between roots and soil at low water potentials. We have recently shown that root hairs facilitate root water uptake in dry soils at high transpiration rates. Our explanation was that root hairs extend the effective root radius decreasing the flow velocity at the root surface and hence the drop in matric potential across the rhizosphere.

To test this hypothesis, we used synchrotron X-ray CT to image the distribution of root hairs in soils. The experiments were conducted with two maize genotypes (with and without root hairs) grown in two soil textures (loam vs sand). Segmenting the different domains within the high-resolution images enabled us to quantify the contact area of the root surface and root hairs with the soil matrix at different water potentials. Furthermore, we calculated the geodesic distance between the root and the soil matrix as a proxy of the accessibility of water to the root.

The results show that root hairs increase the total root surface by approx. 30% and the contact area with the soil matrix by approx. 40%. Furthermore, the average distance from the soil to the root surface decreases by approx. 40% due to hairs, which is the effect of root hairs preferentially growing through macropores. In summary, root hairs not only increase the root surface and the root-soil contact area, but also bridge the air-filled pores between the root epidermis and the soil matrix, thus facilitating the extraction of water.  On top of that, the segmented CT images are also the basis for image-based models aiming at quantifying root water uptake and the effect of root hairs.

References

• (1) Koebernick N, Daly KR, Keyes SD, et al. 2019. Imaging microstructure of the barley rhizosphere: particle packing and root hair influences. New Phytologist 221, 1878–1889.
• (2) Carminati A, Benard P, Ahmed MA, Zarebanadkouki M. 2017. Liquid bridges at the root-soil interface. Plant and Soil 417, 1–15.

How to cite: Duddek, P., Ahmed, M., Zarebanadkouki, M., Koebernick, N., Lovric, G., and Carminati, A.: Root hairs bridge the gap between roots and soil water, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11660, https://doi.org/10.5194/egusphere-egu2020-11660, 2020.

Complex plant-soil interactions can be visualized and quantified by combined application of different non-invasive imaging techniques. Oxygen, carbon dioxide and pH gradients in the rhizosphere can be observed with fluorescent planar optodes, while neutron radiography detects small-scale heterogeneities in soil moisture and its dynamics. Respiration and exudation rates can vary between roots of different types, such as primary and lateral roots, as well as along single roots among the same plant. The 3D root system architecture is therefore a key information when studying rhizosphere processes. It can be captured in detail with neutron tomography, but so far only for plants grown in small, cylindrical containers.

Combined non-invasive imaging of biogeochemical dynamics, soil moisture distribution and 3D root system architecture is a technical challenge. Thin, slab-shaped rhizotrons with relatively large vertical and lateral extension are well suited for optical fluorescence imaging, allowing for spatially extended observation of biogeochemical patterns. This rhizotron geometry is, however, unfavorable for standard 3D tomography due to reconstruction artefacts triggered by insufficient neutron transmission when the long side of the sample is aligned parallel to the beam direction.

We therefore applied neutron laminography, a method where the rotational axis is tilted, to measure the root systems of maize and lupine plants grown in slab-shaped glass rhizotrons (length = 150 mm, width = 150 mm, depth = 15 mm) in 3D. In parallel, we investigated rhizosphere oxygen dynamics and pH value via fluorescence imaging and assessed soil moisture distribution with neutron radiography.

Neutron laminography enabled the 3D reconstruction of the root systems with a nominal spatial resolution of 100 µm/pixel. Reconstruction quality strongly depended on root-soil contrast and hence soil moisture level. After reconstruction of the root system and co-registration with the fluorescence images, first results indicate that observed oxygen concentrations and pH gradients depend on root type and individual distance of the roots from the planar optode.

In conclusion, neutron laminography is a novel 3D imaging method for root-soil systems grown in slab-shaped rhizotrons. The method allows for determining the precise 3D position of individual roots within the rhizotron and can be combined with 2D imaging approaches. Following experiments will address X-ray laminography as a possible attractive further application.

How to cite: Bereswill, S., Rudolph-Mohr, N., Tötzke, C., Kardjilov, N., Hilger, A., and Oswald, S.: Novel 3D imaging of root systems grown in slab-shaped rhizotrons, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21419, https://doi.org/10.5194/egusphere-egu2020-21419, 2020.

We  study  the coupled  action of  water  uptake  and root  development  of  maize  in Rhizotrons under greenhouse conditions. Questions we aim to answer are: What is the effect of a vertical soil moisture gradient on the root growth? How does the root structure in turn influence soil moisture? Do constant  irrigation  quantities and depths eventually lead  to  constant  root  distributions and soil moisture profiles?

We apply highly controlled subsurface irrigation schemes in potting soil-sand mixtures and measure the real-time response of the interdepending soil moisture fields and root structures.

Following a top-down approach, in which the overall behaviour of the coupled system is carefully investigated and described, we aim to unravel the complex soil-root-interaction system. Looking at the occurrence of steady states and continuities sheds light on the type of the underlying feedback loops, which in turn provides insight into the fundamental processes that underlie the typical behaviour. We are particularly interested in trade-offs between the development of rooting depth and rooting density (including its dependency on soil moisture profiles) and the coupled effect of roots and root structures on the infiltration capacity of the soil-root-system. Preliminary results suggest the possibility of an enhancing feedback loop between these processes. 

The next step will be to develop a numerical model that incorporates the interactions that were identified experimentally. The model will allow us to study the behavior and sensitivities of the system in more detail.

How to cite: Maan, D. C., ten Veldhuis, M., and van de Wiel, B.: Unravelling the complex interactions between root development and soil moisture profiles in the soil-root-system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13397, https://doi.org/10.5194/egusphere-egu2020-13397, 2020.

The determination of citrate exuded from soil-grown roots is very challenging due to its rapid microbial degradation and mineralization, sorption to the solid soil phase and ongoing release of organic molecules from organic matter breakdown. For this reason, our knowledge about citrate release is mainly based on experiments carried out in hydroponics. Results obtained in hydroponics cannot directly be transferred to soil-plant systems, as hydroponics represents an artificial environment. This study aimed to develop a localization and quantification technique for citrate exuded from soil-grown plant roots, based on diffusive gradients in thin film (DGT). Polyacrylamide gels containing precipitated zirconium hydroxide (ZrOH) were applied to the rhizosphere of soil grown plants, on which citrate is efficiently immobilized, thereby creating a zero sink to sample the citrate exuded from the roots. Citrate was eluted with 1 mL 0.5 mol L^-1 NaOH from the ZrOH gel and quantified by ion chromatography. ZrOH gel discs were able to bind the citrate contained in 10 mL of 2.77 mg citrate L^-1 solutions within a 4h uptake period. Elution efficiency was ~89%. ZrOH gel capacity at pH 8 was 200 µg per gel disc and 299 µg per gel disc at pH 4, which is sufficient to act as a zero sink for citrate released from plant roots. As a first exemplary method application, we grew white lupin plants in rhizotrons using a highly phosphorus deficient soil. ZrOH gel sheets were applied for 26 h onto cluster roots for citrate sampling following established DGT protocols. Gels were cut afterwards into 5×5 and 5×2 mm slices for obtaining a citrate exudation map. In both cases we were able to localize and quantify up to 7.89 µg citrate on individual gel slices, as well as to identify longitudinal and lateral citrate gradients around the cluster roots. Moreover, the characterization of ZrOH gels showed its suitability for citrate sampling in terms uptake kinetics and capacity. These results demonstrate that the developed method is suitable for citrate sampling and localization in a non-destructive way from soil-grown plant roots. As it is applicable to soil grown-roots and provides unprecedented spatial resolution, this sampling technique advances the experimental possibilities for researching root exudates considerably. Using suitable binding materials, this approach is also applicable to other carboxylates such as malate or oxalate and other compound classes such as phenolics, flavonolos etc. Furthermore, this technique can be combined with complementary imaging methods for mapping e.g. nutrients, contaminants, pH or enzyme activity distributions.

How to cite: Tiziani, R., Puschenreiter, M., Smolders, E., Mimmo, T., Herrera, J. C., Cesco, S., and Santner, J.: Quantifying and mapping citrate exudation in soil-grown root systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14587, https://doi.org/10.5194/egusphere-egu2020-14587, 2020.

Physical properties of soil such as penetration resistance and oxygen concentration of soil air strongly influence root system development in plants. Soils typically exhibit considerable spatial and temporal fluctuations in penetration resistance and oxygen concentration of soil air due to wetting-drying cycles, small-scale differences in soil compactness or hotspots of biological activity. Hence, roots of a single plant are exposed to different physical environments and thus physical stresses during their growth through the soil profile. Plants are known to adjust their root development to these spatiotemporal fluctuations in soil physical conditions. Such phenotypic adjustments include changes of root growth rate as well as alterations of root morphology and anatomy. However, these adjustments reduce accessibility of water and nutrients and may increase the carbon demand for soil exploration, which limits aboveground plant development. Until now, it is unclear whether such adjustments in root development are plastic (i.e. the phenotype is irreversibly changed even when roots re-enter zones with optimal growth conditions) or elastic (i.e. the phenotype is only temporarily changed and recovers again when roots re-enter zones with optimal growth conditions).

To investigate the plasticity and elasticity of root development, we designed customized microrhizotrons in which soil penetration resistance and the concentration of oxygen in soil air can be varied. Near-infrared (λ=830 nm) time-lapse imaging was applied to quantify root growth rates, and combined with measurements of root morphology and anatomy. A series of experiments was conducted using different crop species with contrasting root system properties (fibrous vs. taproot system, thin vs. thick roots). After an establishment period of three days under optimal growth conditions, roots were exposed for 24 hours to increased penetration resistance, hypoxia and the combination of both stresses. Following this, the stress was released, and plants continued to grow for 24 hours at optimal conditions, before a second stress was applied for another 24 hours. Generally, root development responded to changes in soil physical conditions across all species. However, depending on the species, the adjustments in root development were found to be constant or temporary, i.e. plastic or elastic. This difference between species was particularly pronounced for root growth rate. Root growth rate in pea recovered after soil physical stress was released, while root growth rate in wheat remained low after stress release. The obtained findings will be discussed with respect to the tolerance of different plants to soil physical stress as well as the effects of root growth on soil structure dynamics.

How to cite: Colombi, T., Sjulgård, H., Iseskog, D., and Keller, T.: Root development under fluctuating soil physical stress – plastic and elastic responses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19056, https://doi.org/10.5194/egusphere-egu2020-19056, 2020.

In the face of global climate change, a well-informed knowledge of plant physiologic key parameters is essential to predict the behavior of ecosystems in a changing environment. Many of these parameters may be determined with lab or pot experiments, but it could prove problematic to transfer results obtained in a such experiments with small trees to fully grown trees. Therefore, new approaches to determine relevant parameters for mature trees are still required. Regarding plant water uptake, parameters related to fine root distribution (maximum depth, depth distribution and rhizosphere radius) and parameters describing the physiological limits of root water uptake are important, but usually hard or costly to assess for fully grown trees.  In-situ isotope probes (Volkmann et al. 2016a  & 2016b) are a promising recent development that offer new possibilities for the investigation of plant water uptake and associated physiological parameters.

In this study we used in-situ stable water isotope probes in soil (six depths from 10 to 100 cm) and in tree xylem of mature (140 years) European beech trees (three heights between 0 and 8 m). With those probes, we monitored soil and xylem isotope signatures after an isotopically labeled (Deutrium-Excess = 100 ‰) irrigation pulse equivalent to 150 mm of precipitation and foursubsequent natural precipitation events over a period of twelve weeks with a high temporal resolution (six or more measurements per probe per day). Those measurements were complemented with measurements of soil moisture and sap flow dynamics. We interpolated our measured soil isotope and soil moisture data in order to obtain spatially and temporally continuous data for those soil parameters. Then we used this data as an input to the Feddes-Jarvis plant water uptake model, in order to predict the isotopic signature of plant water uptake at daily time steps. With the help of our observed isotopic signatures, we were able to directly constrain the critical water potential parameter of the Feddes model as well as the underlying fine root distribution. Furthermore, the observed dampening of the breakthrough curve of our Deuterium-labeling pulse allowed us to infer information on the rhizosphere  radius and water transport velocities in the fine roots and stem between the points of root water uptake and the eight meter stem height.

With our field experiment we showed that in-situ isotope measurements in soil profiles and in tree xylem sap can help to constrain plant water uptake modelling parameters. Future experiments might use this approach to scrutinize lab-scale derived hypothesizes regarding tree water uptake and to investigate the temporal and spatial dynamics of root water uptake in the field.

Volkmann, T. H., Haberer, K., Gessler, A., & Weiler, M. (2016a). High‐resolution isotope measurements resolve rapid ecohydrological dynamics at the soil–plant interface. New Phytologist, 210(3), 839-849. 

Volkmann, T. H., Kühnhammer, K., Herbstritt, B., Gessler, A., & Weiler, M. (2016b). A method for in situ monitoring of the isotope composition of tree xylem water using laser spectroscopy. Plant, cell & environment, 39(9), 2055-2063. 

Jarvis, N. J. (1989). A simple empirical model of root water uptake. Journal of Hydrology, 107(1-4), 57-72. 

How to cite: Seeger, S., Rinderer, M., and Weiler, M.: Inferring plant physiologic parameters for root water uptake modelling from high frequency in-situ isotope measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22007, https://doi.org/10.5194/egusphere-egu2020-22007, 2020.

The combination of functional-structural root-system models with root architectures derived from non-invasive imaging is a promising approach for gaining a better understanding of root-soil interaction processes. However, root architectures can often not be fully recovered using imaging, which subsequently affects the assessment of function via the functional-structural root models. In this study, we explored theoretical and actual possibilities of root system reconstruction from MRI and X-ray CT images. Experiments with water-filled capillaries showed the same minimum detectable diameter for both MRI and X-ray CT for the used parameter setup. Experiments with soil-grown lupine roots, however, showed significantly lower root system recovery fractions for MRI than for X-ray CT, from which most roots thicker than 0.2 mm could be recovered. MRI allowed root signal detection below voxel resolution; however, the connection of this signal to a continuous root structure proved difficult for large, crowded root systems. Furthermore, soil moisture levels >30% hampered root system recovery from MRI scans in experiments with pure sand. To overcome the problem of low root system recovery fractions, we developed a new method that uses incomplete root systems as a scaffold onto which missing roots are simulated using information from WinRhizo measurements. Comparisons of root length within subsamples of semi-virtual root systems and root systems derived from X-ray CT scans showed good agreement. Evaluation of hydraulic root architecture measures of incomplete root system scaffolds and semi-virtual root systems proved the importance of using complete root system reconstructions to simulate root water uptake. Semi-virtual root reconstruction thus appears to be a promising technique to complete root systems for subsequent use in functional-structural root models.

How to cite: Landl, M., Huber, K., Pohlmeier, A., Vanderborght, J., Pflugfelder, D., Roose, T., and Schnepf, A.: Reconstructing root system architectures from non-invasive imaging techniques for the use in functional structural root models , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-693, https://doi.org/10.5194/egusphere-egu2020-693, 2020.

A central component of the rhizosphere is root mucilage, a hydrogel exuded by plants that dramatically alters chemical and physical properties of the soil. It is characterized by its large water holding capacity and is hydrophilic or hydrophobic depending on its hydration status: when swollen, mucilage is hydrophilic but becomes hydrophobic when dry, forming local hydrophobic spots on the surface of soil particles. The morphology of these hydrophobic regions formed by dried mucilage is affected by the type of mucilage and microorganisms and can vary from isolated local spots, to networks spanning across larger areas of the soil particle surface. However, until now the understanding on how this heterogeneous distribution and its morphology affect water retention and water repellency in soil is limited.

Therefore, the goal of this study is to investigate the impact of the spatially heterogeneous interfacial tension distributions on the capillary rise in soil. We utilize a two phase flow model based on the Lattice-Boltzmann to numerically simulate capillary rise between parallel slides having a heterogeneous distribution of interfacial tension during imbibition and drainage.

The simulations allow us to quantitatively evaluate how heterogeneous micro-scale distributions of interfacial tension affect the macro-scale water retention behavior. This we could approximately explain with three hypotheses: The equilibrium capillary rise volume (i) is a measure for the hydrophilicity of a field, (ii) capillary rise is affected by the standard deviation of the interfacial tension field, (iii) hysteresis is induced by the heterogeneous field and depends on the correlation length of the patterns.

In future, simulations will be extended also to the geometry of real soil.

How to cite: Bentz, J., Kroener, E., Patel, R., and Haupenthal, A.: How heterogenous distributions of hydrophobicity affects the capillary rise in soil , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13701, https://doi.org/10.5194/egusphere-egu2020-13701, 2020.

In the course of climate change, the occurrence of extreme weather events is expected to increase. Drought tolerance of crops and careful irrigation management are becoming key factors for global food security and the sustainable resource use of water in agriculture. Root water uptake plays a vital role in drought tolerance. It is influenced by root architecture, plant and soil water status and their respective hydraulic properties. Models of said factors aid in organizing the current state of knowledge and enable a deeper understanding of their respective influence on crop performance. Water uptake by roots leads to a decrease in soil moisture and may cause the formation of soil water potential gradients between the bulk soil and the soil-root interface. Although the Richards equation in theory takes these gradients into account, a very fine discretization of the soil domain is necessary to capture these gradients in simulations. However, especially during drought stress, the drop in hydraulic conductivity in the rhizosphere could have a major impact on the overall water uptake of the root system. In order to investigate computationally feasible alternative approaches for simulations with source terms that take these hydraulic conductivity drops into account, we conducted experiments with lupine plants. The root architecture of the growing plants was measured several times using an MRI. Subsequently, these MRI images were used in a holobench for manual tracing of the roots. We were able to mimic the root growth between the measurement dates using linear interpolation. In addition to root architecture, soil water contents and transpiration rates were monitored. We then used this data to systematically compare the computational effort of different approaches to consider the hydraulic conductivity drop near roots in terms of accuracy and computational cost. Eventually we aim at using these results to improve existing root water uptake models for the presence of hydraulic conductivity drops in the rhizosphere in an efficient and accurate way.

How to cite: Selzner, T., Landl, M., Pohlmeier, A., Leitner, D., Vanderborght, J., and Schnepf, A.: Functional-structural modelling of root water uptake based on measured MRI images of root systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21295, https://doi.org/10.5194/egusphere-egu2020-21295, 2020.

Minimizing water limitation during growth of agricultural crops is crucial to unlocking full yield potentials. Crop yield losses vary according to timing and severity of water limitations, but even short-term droughts can be a major cause of yield losses. While the potential influence of deep roots on water uptake has been highlighted numerous times, the actual contribution of deep roots to water uptake is yet to be revealed. The objective of this study is to get an understanding of what limits deep water uptake by deep-rooted crops under topsoil water limitations.

We found that deep-rooted crops experience water limitations despite access to water stored in the deep soil and we hypothesize that deep water uptake by deep-rooted crops is limited by 1) the hydraulic conductivity of the deeper part of the root zone, arising from limited root length density in combination with the hydraulic resistance of the roots or 2) by a hormonal response arising from the plant sensing dry conditions in the shallow soil leading to stomata closure, to conserve water. The two hypotheses can of course not be valid simultaneously, but both might be valid under certain conditions, at certain times or for certain species.

In a large-scale semi-field setup, we grow oil seed rape and by combining measures of root development, root hydraulic conductivity, transpiration, stomatal conductance, ABA concentrations and soil water content from a large scale semi-field setup with a mechanistic 3-D root-soil modelling approach (R-SWMS), we are able to us distinguish various scenarios and to evaluate what limits deep water uptake.

How to cite: Rasmussen, C., Rosenqvist, E., Liu, F., Bodin Dresbøll, D., Thorup-Kristensen, K., and Javaux, M.: What limits deep water uptake by deep-rooted crops? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20096, https://doi.org/10.5194/egusphere-egu2020-20096, 2020.

Minirhizotron (MR) imaging systems are key instruments to study the hidden half of plants and ecosystems, i.e. roots, mycorrhiza and their interactions with pathogens, fauna etc. in the rhizosphere. However, despite scarce data on the ‘hidden half’ of plants and ecosystems, e.g. needed for better understanding species’ ecophysiology, breeding resource efficient crops or determining soil C input, the technological advances remained yet limited.

We designed and build an automatic, modular MR camera system for permanent operation in situ, combining state-of-the-art imaging sensors (UHD VIS and certain near infrared (NIR) wavebands) with mechatronic automation to allow for effective and precise imaging of MR tubes. The system consists of a MR camera ‘carrier system’ (i.e. for camera positioning, scheduling and processing of images, interconnectivity) for 7 cm diameter, up to 2 m long, MR tubes installed in situ (fields to forests), and two interchangeable camera modules to be used with the carrier system. The first module is a cost-effective UHD RGB module and the second module combines VIS and selected multispectral (NIR) wavebands--potentially allowing for advanced image processing such as root classification (age, branching order etc.) and approximation of selected soil properties (soil water content, C contents etc.).

The presented technology has the potential to benefit society both indirectly via improving the capacity of the research community to study root and rhizosphere systems (e.g. in a C budgeting, or plant breeding context), and is, beside automatic image analysis, a prerequisite for making root development information available to stakeholders in real time (e.g. to farmers for precision irrigation). Additional benefits of an automatic MR system such as precise stitching (for creating ‘panoramic’ images) and creation of ‘super resolution’ images are discussed.

How to cite: Rewald, B., Lazarovitch, N., Baykalov, P., Hadar, O., Mayer, S., Bodner, G., and Seehra, L.: Automatizing MiniRhizotron Image Acquisition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21832, https://doi.org/10.5194/egusphere-egu2020-21832, 2020.

The pathways of water across root tissues and their relative contribution to plant water uptake remain debated. This is mainly due to technical challenges in measuring water flux non-invasively at the cellular scale under realistic conditions.  We developed a new method to quantify water fluxes inside roots growing in soils. The method combines spatiotemporal quantification of deuterated water distribution imaged by rapid neutron tomography with an inverse simulation of water transport across root tissues. Using this non-invasive technique, we estimated for the first time the in-situ radial water fluxes [m s^-1] in apoplastic and cell-to-cell pathways. The water flux in the apoplast of twelve days-old lupins (Lupinus albus L. cv. Feodora) was seventeen times faster than in the cell-to-cell pathway. Hence, the overall contribution of the apoplast in water flow [m³ s^-1] across the cortex is, despite its small volume of 5%, as large as 57±8 % (Mean ± SD for n=3) of the total water flow. This method is suitable to non-invasively measure the response of cellular scale root hydraulics and water fluxes to varying soil and climate conditions.

How to cite: Zarebanadkouki, M., Trtik, P., Hayat, F., Carminati, A., and Kaestner, A.: Root water uptake and its pathways across the root: quantification at the cellular scale , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13520, https://doi.org/10.5194/egusphere-egu2020-13520, 2020.

Better management practices have been used to increase soil water storage and reduce evaporation from the soil surface to optimize crop water use efficiency (WUE) in irrigated agriculture. A field study was conducted to evaluate the effect of  conventional tillage (CT), No-till (NT) and strip tillage (ST) practices on yield, water use (WU) and WUE of sugarbeet (Beta vulgaris L.) on a clay loam soil under over-head sprinkler irrigation system in the northern Great Plains. Tillage treatments were replicated five times in a randomized block design. Seasonal WU and WUE for sugarbeet root and sucrose yield were determined for the 2018 and 2019 growing seasons according to the water balance and WUE equations under three tillage practices. Results showed that no significant differences due to tillage treatment were found for crop WU, root yield, sucrose yield, and WUE for sugarbeet root and sucrose in 2018 and 2019 growing seasons. In 2019, the average value of WU across three tillage systems (616 mm) was significantly greater relative to 2018 (468 mm) due to atypical large rainfalls (218mm) occurred in September of 2019. Consequently, WUE values for both root and sucrose yield in 2019 under CT, NT, and ST were significantly greater than those in 2018. While NT and ST practices are promising alternative to CT for agricultural production in this region, further research is needed prior to making any recommendation.

How to cite: Jabro, J., Stevens, B., Iversen, B., Allen, B., and Sainju, U.: Irrigated sugarbeet yield, water use and water use efficiency responses to tillage practices, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1259, https://doi.org/10.5194/egusphere-egu2020-1259, 2020.

Salinity affects plant growth due to both osmotic and ionic stress. The root system is essential in defense mechanisms against salinity, particularly involving salt ion avoidance or exclusion. Jojoba (Simmondsia chinensis) displays significant resistance to salinity. In the present study, Jojoba was planted in 60-L plastic buckets containing perlite growth medium and were provided with eight distinct salinity levels using two operating tanks of final irrigation solutions. Response of Jojoba to salinity was measured in above ground parameters and in roots using minirhizotron access tubes and imaging analysis. Leaf phosphorous and potassium concentrations decreased with increasing salinity level while leaf manganese, calcium, sodium and chloride concentrations increased with irrigation salinity level. Jojoba plants were found to have high level of storage of salt minerals in leaves but without effects on photosynthesis or transpiration. Roots exhibited different distribution patterns under different salinity treatments. Root length density increased with increased salinity at each depth. Root number and root length increased over time. During spring, the plant growth was faster than winter. Root diameter decreased over time due to new root development. Time had a more significant effect on root length density than irrigation water salinity or soil depth. Root number and root length were not significantly affected by the salt treatments.

How to cite: Ephrath, J., Ben-Gal, A., Bustan, A., and Zhao, L.: Root and Shoot Responses to Salt Stress in Jojoba (Simmondsia chinensis) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1669, https://doi.org/10.5194/egusphere-egu2020-1669, 2020.

Compared to bulk soil, rhizosphere has different properties because of the existence of root mucilage which affects the physical, chemical and also microbial processes. Hydraulic phenomena like limiting water flow at certain dry soil conditions, modulating extreme water contents by slow response to water potential changes; and also influencing solute transport and gas diffusion by varying the connectivity of liquid and gas phases are all classified under the set of the physical processes which are affected by mucilage in the rhizosphere.

Overview of the literature and previous models shows the lack of a three-dimensional pore-scale dynamic model for a better understanding of the connectivity between different phases during imbibition and drainage processes. A major challenge is that mucilage shows a complex behavior which at low concentrations is more like a liquid while at higher concentration when it is almost dry, it becomes a solid.

In particular, this study will use the Lattice Boltzmann method as a powerful tool for fluid dynamics study and the discrete element method for describing solids to present a pore-scale model for more accurate simulation and study of physical processes in the rhizosphere.

How to cite: Esmaeelipoor Jahromi, O., Bentz, J., Haupenthal, A., Patel, R., and Kroener, E.: Pore scale simulations of how mucilage alters connectivity of liquid and gas phase in the rhizosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15591, https://doi.org/10.5194/egusphere-egu2020-15591, 2020.

Banana is a very important crop in East-Africa, serving as a staple for millions of smallholder farmers. Aside from pests and diseases, lack of water is the major constraint to production. Climate change is expected to aggravate these problems, creating a need for improved resilience and better management practices. A major obstacle to the development and evaluation of such practices is the difficulty to measure drought stress in the field. In this research, we investigate physiological parameters that can provide information on drought stress in banana under field conditions. We evaluate the use of stable carbon isotope ratios (δ¹³C) and leaf temperature as indicators for stress, the former ones not well-established for banana. Leaf temperature is known to increase under drought stress due to stomatal closure. The existing methods to measure leaf temperature are however expensive and their use is limited to small greenhouse set-ups. In this research, we employ an infrared thermometer (±1°C) for temperature measurement under field conditions. The experimental set-up consists of a banana field trial with a blocked design (irrigated and rainfed treatments) in the Kilimanjaro region, Tanzania. Leaf samples for isotope analysis were taken from mature plants (mother plants) and the main on-growing sucker (daughter plants) in August 2019, during the dry season. Leaf temperature was monitored throughout the day. Results show significantly higher δ¹³C ratios in rainfed plants, compared to irrigated ones, indicating more drought stress. Within both groups, mother plants have higher δ¹³C ratios than daughter plants. At dawn, leaf temperature was similar for all treatments. During the day, rainfed banana plant leaf temperature increased 7°C more than in their irrigated counterparts. Daughter plants remained cooler than mother plants in both treatments. Leaf temperature and δ¹³C showed a strong correlation. While carbon isotope signatures are a known proxy, our results suggest that leaf temperature is a an easily measurable indicator of drought stress as well. The infrared thermometer is cheap, convenient to use in the field and provides in-situ information. Leaf temperature has an enormous potential as a drought stress sensor in banana, as well as in other plants. Our research will further optimize both methods for drought stress evaluation. This will facilitate management comparisons in the future as well as variety screening, eventually contributing to more resilient banana production systems.

How to cite: Vantyghem, M., Merckx, R., Hood-Nowotny, R., Stevens, B., Resch, C., Roman, G., and Dercon, G.: Innovative physiological indicators for drought stress in banana , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4844, https://doi.org/10.5194/egusphere-egu2020-4844, 2020.

Earth system models struggle to accurately predict soil-root water flows, especially under drying or heterogeneous soil moisture conditions, resulting in inaccurate description of water limitation of terrestrial fluxes. Recent descriptions of plant hydraulics address this by applying Ohm’s law analogues to the soil-plant-atmosphere hydraulic continuum.

While adequate for stems, this formulation linearises soil-root and within-root resistances by assumption, neglecting the nonlinearity of pressure gradients in absorbing roots. The resulting discretisation error is known to depend strongly on model spatial resolution. At coarse resolution, substantial errors arise in a form depending on the assumed configuration of resistances. In simulations of a drought at the Wind River Crane (WRC) flux site, a parallel Ohm model based on the rooting profile overpredicted hydraulic redistribution, while a series model overpredicted uptake in shallow layers at the expense of deep ones.

A conceptual alternative is to upscale exact solutions to the hyperbolic differential equation that describes root water uptake, by solving for the mean root water potential in each soil subdomain. Upscaled solutions show that multiple soil water potentials affect pressure gradients in each root segment, producing the nonlinearities absent in Ohm models. This upscaled model gave better predictions of WRC drought data and was significantly less prone to over-fitting than the two Ohm models, with more robust predictions beyond calibration conditions.

Analysis reveals classes of root systems of differing architectural complexity that yield a common upscaled model. In numerical experiments, using a simple upscaled model in situations of increasing complexity (e.g., adding individual plants), resulted in bounded errors that decreased asymptotically with increased complexity. The approach is thus a viable candidate for upscaling the effects of heterogenous soil moisture distributions on root water uptake.

How to cite: Bouda, M. and Javaux, M.: Upscaled exact solutions to root water uptake equations for earth system modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5496, https://doi.org/10.5194/egusphere-egu2020-5496, 2020.

Soils play a key role in the provision of vital ecosystem services. Soil functions, that deliver these services, are governed by soil properties.  Soil structure is a fundamental property of soils since it controls water, geochemical and biological processes.  The soil pore system, one of the main components of soil structure, can be affected by different biological feedbacks. Vegetation can have an impact on soil pore system through changes in pore size distribution and porosity, causing differences in soil hydraulic properties as well as soil-water processes.

In high elevation tropical Andean ecosystems (páramos) little is still known about vegetation feedbacks on soil properties. At high elevation páramos (above 4100m), it is possible to find high diversity and co-dominance of plant species over short distances. In these landscapes, cushion plants and tussock grasses dominate alongside shrubs. These vegetation types, adapted to extreme local climatic conditions, are placed on young volcanic soils. We take advantage of this diverse setting, located within Antisana´s water conservation area in the north of Ecuador, by studying soil hydraulic properties and soil pore system in eight soil profiles. We hypothesize that the effect caused by Calamagrostis intermedia (tussock) and Azorella pedunculata (cushion) species on soil pore system and soil hydraulic properties at different horizons will be statistically different. In addition, we explore these effects in relation to other soil's physical properties and root traits.

Soil hydraulic properties were determined on the basis of field observed saturated hydraulic conductivity as well as based on water retention contents at saturation (porosity), field capacity and permanent wilting point measured in the laboratory by the multi-step outflow method and the porous membrane pressure cell. Furthermore, water retention curves were fitted to measured data by the bimodal van Genuchten model. Based on these fittings the pore size distribution was determined. Equivalent pore diameters were derived from the soil water tension head via the capillary rise equation. Statistical analysis to determine differences was carried out by means of the Mann-Whitney U test.        

The results show that measurable differences in soil hydraulic properties and soil pore system between vegetation species are present at the upper soil horizons, while they become negligible at greater depth. These differences are mainly related to bulk density and root traits. Based on this baseline study, further research could elucidate the effects of vegetation species on soil-water processes at high elevation páramo landscapes and will contribute to enhancing water resources management.

How to cite: Páez-Bimos, S., Vanacker, V., Villacís, M., Morales, O., Calispa, M., Salgado, S., Delmelle, P., and Molina, A.: Impact of vegetation species on soil pore system and soil hydraulic properties in the high Andes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6284, https://doi.org/10.5194/egusphere-egu2020-6284, 2020.

Plant transpiration and root water uptake are dependent on multiple traits that interact with site soil characteristics and environmental factors such as radiation, atmospheric temperature, relative humidity, and soil-moisture content. Models of root architecture and functions are increasingly employed to simulate root-soil interactions. Root water uptake is thereby affected by the root hydraulic architecture, soil moisture conditions, soil hydraulic properties, and the transpiration demand as controlled by atmospheric conditions. Stomatal conductance plays a vital role in regulating transpiration in plants. We performed simulations of plant water uptake for plants having different mechanisms to control transpiration, spanned by isohydric/anisohydric spectrum. Isohydric plants follow the strategy to close their stomata in order to maintain the leaf water potential at a constant level, while anisohydric plants leave their stomata open when leaf water potentials fall due to drought stress. Modelling the stomatal regulation effectively will result in a more reliable model that will regulate the excessive loss of water. We implemented hydraulic and chemical stomatal control
of root water uptake following the current approach where stomatal control is regulated by simulated water potential and/or chemical signal concentration. In order to maintain water uptake from dry soil, low plant water potentials are required, which may lead to reversible or permanent cavitation. We parameterise our model with field data, including climate data and soil hydraulic properties under different tillage conditions. This helps us to understand the behaviour of different crops under drought conditions and predict at which growing stage the stress hits the plant. We conducted the simulations for different scenarios to study the effect of hydraulic and chemical regulation on root system performance under drought stress.

How to cite: Khare, D., Bodner, G., Javaux, M., Vanderborght, J., Leitner, D., and Schnepf, A.: Quantifying how plants with different species-specific water-use strategies cope with the same drought-prone hydro-ecological conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9364, https://doi.org/10.5194/egusphere-egu2020-9364, 2020.

Trees as essential components of green urban structures are of crucial importance for the regulation of the urban climate and human wellbeing. Despite this, the currently rising demand for living space and infrastructure causes an increase in the share of sealed and compacted soils. These trends directly affect soil-plant interactions in urban environments. The synergy of the increasing land use pressure and changing climatic conditions worsen the site and growth conditions and thus the vitality for young and mature trees. A possible adaptation strategy is the transformation of plant pits into water reservoirs combining the discharge of excess water with impermeable sole materials and substrates that optimise the water conductivity and storage capacity. The corresponding aim of this study is the quantification of the effects of the water balance dynamic in the rooting zone on the vitality of young trees at highly sealed sites in the city of Hamburg. The two main questions are 1) Do technically modified plant pits reduce summerly drought stress inside the rooting zone and thus improve the root water uptake and tree vitality?, and 2) Does excess water after high rainfall limit the gas exchange and thus the root growth? To answer these questions, we selected two different sites, one residential area and one pedestrian zone, which differ regarding the type of excess water discharge. Overall, two technically modified plant pit variants will be compared with generally constructed variants. Each site will be characterized by soil physical and chemical parameters. Additionally, each plant pit is equipped with TDR- and water tension probes for a continuous monitoring of the soil water balance and O₂ as well as CO₂ probes for monitoring the gas household. Rhizotrones and dendrometers in combination with Δ13C isotope analysis and stomatal resistance will help to investigate the tree vitality. The data will be used for modelling local water balance dynamics under expected climatic scenarios and for evaluating the different plant pit variants. Development as well as dimensioning recommendations for prospective plant pit constructions, improving the soil-plant interaction, will be derived.

How to cite: Nofz, I. A., Kleinschmidt, V., Becker, J. N., and Eschenbach, A.: Impacts of technically modified plant pits on water balance dynamics and tree vitality in urban environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11087, https://doi.org/10.5194/egusphere-egu2020-11087, 2020.

The effect of vegetation on the volumes of water that infiltrates into the soil has been extensively studied, but not the redistribution that occurs radially from trees. This is especially important in arid and semi-arid areas where water volumes are scarce and water resources management must be more scrupulous. In the present study, the influence of native vegetation (huizache trees) on the redistribution of infiltration in a semi-arid zone in the central Mexican plateau was analyzed. Single ring infiltration tests were carried out with a radial distribution in 2 trees: 4 located inside the crown of the tree and 4 outside it, in 4 different axes, giving a total of 32 tests per tree. Likewise, particle size distribution and soil texture analysis were carried out in 4 orthogonal directions and dry bulk density and initial water content tests at each sampling point were performed. The results showed a zone of influence located between r / 2 and r of the tree canopy, where the infiltration is much greater compared to the other points. Based on these results, the methodology for a third tree was redesigned, in order to characterize various infiltration areas. So that 3 zones were established within the tree: near, intermediate and far, taking 2 tests in each zone, in orthogonal direction, and taking a test in each zone of 4 additional axes, a total of 36 tests. The results of the infiltration tests with this methodology showed similar results to the other two trees: low infiltration rates close to the tree trunk, high infiltration rates in the area between r / 2 and r of the canopy and again low rates of infiltration in the area outside the crown. Additionally, the particle size distribution analyzes showed the presence of 4 types of soil: loam, sandy-loam, clay-loam and silt-loam soil. On the other hand, the initial water content and dry bulk density do not seem to affect the infiltration process to a greater extent and they vary indiscriminately. The above suggests that the area between r / 2 and r is the one that captures the highest infiltration volumes, it may be due to the shadow effect produced by the treetops, although the soil texture has an influence on the infiltration rates, it does not influence the form of radial redistribution of tree infiltration.

How to cite: Garcia Perez, A. B., Gonzalez Sosa, E., Breil, P., and Braud, I.: The role of vegetation in the redistribution of infiltration in a semi-arid zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11573, https://doi.org/10.5194/egusphere-egu2020-11573, 2020.

ABSTRACT    

Slope stability of forested areas is often determined by tree root strength. After landslides, the early successional species emerged first, followed by the late successional species. This study aimed to examine whether tree root strength varies as tree species change along with the succession sequence. The study site is in the Lienhuachi Experimental Forest in central Taiwan, where multiple landslides happened in 2008. Three dominant early (Mallotus paniculatus, Sapium discolor, and Schefflera octophylla) and three late successional species (Cryptocarya chinensis, Engelhardtia roxburghiana, and Randia cochinchinensis) were sampled to conduct the single-root-pull-out tests in the field. Root strength which varies with root diameters was estimated with the Root Bundle Model with the root-failure Weibull survival function (RBMw). Results showed that the overall root strength of the early successional tree species were higher than that of late successional species only when root diameter was lower than 5.44 mm. However, among the six species, the root strength of Sapium discolor, an early successional species, was highest and the species with the lowest root strength was a late successional species (Engelhardtia roxburghiana). To precisely estimate tree effects on slope stability, our results highlighted the need to collect root strength data specifically for each species, even though it will be a daunting task for areas rich in tree diversity.

Keyword: landslide, Root Bundle Model, vegetation succession

How to cite: Chen, C.-W., Song, G.-Z. M., Chang, L.-W., Ko, C.-J., Lee, H.-T., Hu, H.-Y., and Tseng, J.: Root strength comparison between early and late successional trees in a subtropical forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13073, https://doi.org/10.5194/egusphere-egu2020-13073, 2020.

Wetlands are important sites for the biogeochemical cycles of macro and microelements, because the presence of the water induces faster chemical and transport processes in the soils which occur as intensive diurnal and seasonal fluctuations of the soil parameters and element-content. Vegetation is also varied basically because of the (often fluctuating) water level, which makes it possible to study these different ecotopes in a relatively small area.

We chose our long-term study site – a meadow formed by a local depression of the surface – near Ceglédbercel, Hungary in 2010. Three different vegetation patches were separated governed by the following species (in order of the influence of water): 1 – Agrostis stolonifera; 2 – Carex acutiformis, Carex flacca, Carex vulpina; 3 – Phragmites australis. Microclimatic and soil-representing parameters were measured in each patch: air temperature, evaporation, strength of wind and incident solar radiation; soil temperature, pH and redox potential of the soil solution. We also analyzed the main elements and element forms of the soil solution regularly: NO₃^-, NO₂^-, NH₄⁺, PO₄^3-, Mn, Fe, K, Na, Mg, Ca and emitted N₂O, CH₄ gas fluxes of the soil.

Our main hypothesis was that different plant species generate measurable differences and heterogeneities in the bulk soil. This is shown best by the run of the redox potential which often seemed to ignore the effect of water-gradient because of the regulating ability of plants in the rooting zone. The occurrence and concentration of nitrogen forms are very redox-sensitive; thus they are seemingly good indicators of the state of the soil. Somewhat surprisingly, diurnal cycles (caused by the plants’ alternating photosynthetic activity) rarely occurred among the measured parameters and concentrations. One of those rare occurrences was the emission of gaseous N₂O, which reached its maximum in the afternoon and almost stopped before dawn. Our long-term experimentation also caught some interesting anomalies (e. g. accidental destruction of the vegetation) thus we managed to record the effect of these environmental changes on the soil and the most environment-sensitive elements of the soil proved to be the nitrogen-forms, with Fe and K.

How to cite: Horváth-Szabó, K., Grosz, B., Ringer, M., and Szalai, Z.: Nitrogen dynamics measurements in wetland soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13491, https://doi.org/10.5194/egusphere-egu2020-13491, 2020.

The mechanical properties of soil and mucilage have a significant effect on root penetration resistance which can become a limiting factor for root growth in dry and compacted soils. Our hypothesis is that the way how root exudates alter penetration resistance in soil is controlled by the interplay of two mechanisms: on the one hand mucilage stabilizes the soil resulting in an increased penetration resistance, on the other hand mucilage holds water, which tends to reduce soil penetration resistance. To quantitatively test our hypothesis we consider fine-grained soil, a needle which has 30º apex angle and another needle with 60º. The needles are used for the penetration of the soil, which is used to simulate the plant root growth in the real condition. Chia seed mucilage was used in the study to mimic the effect of root mucilage. The growth of root was simulated by penetrating the needles at constant speed into the soil using a rheometer. Measurements were repeated for various water contents, compactions and at various mucilage concentrations (0%, 0.1%, 0.3%, 0.5%).

Our experiments show that the concentration of the mucilage affects penetration forces significantly in the soils. Penetration forces are significantly less in the soils for low concentration mucilage (0.1%) and high in the higher concentration mucilage (0.5%). This may be because higher concentration of mucilage stabilizes the loose soil by binding the soil particles together. While the low concentration mucilage softens the soil mass due to the presence of more water and in this way reduces the penetration forces. Results also show the penetration resistance is also significantly affected by root geometry. The 60º needle experienced higher penetration resistance than the 30º needle when the soil is dry and the density of the soil is low. The 30º needle experienced higher penetration resistance than the 60º when the soil wet and the density is high.

How to cite: Mysore Janakiram, R. K., Brax, M., and Kroener, E.: Soil penetration resistance affected by root exudates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16227, https://doi.org/10.5194/egusphere-egu2020-16227, 2020.

The use of minirhizotron (MR) imaging systems is gaining popularity, resulting in a large amount of collected images—which need efficient and accurate processing for root trait extraction. This study proposes a neural network-based solution for automatic measurement of root length in images taken by MR systems. Current root length measurement techniques involve two steps; manually operating the MR for taking the images, and manually annotating roots in front of a noisy rhizosphere ‘background’ with a dedicated software. As the analysing process is extremely time consuming, automation can both lower the costs and facilitate greater temporal resolution.

Using convolutional neural networks (CNN) in image classification tasks has become very common due to its simplicity, yet regression tasks are still considered difficult. We propose a new model that combines the strength of conditional learning, transfer learning and bagging in order to achieve a precise regression. The dataset used holds 12,000 highly diverse images of 5 tomatoes cultivars, which were collected by a BARTZ minirhizotron camera over a period of 4 months.

Initial results show a success rate of 75% accuracy with 33 mm Mean Absolute Error (MAE). Error analysis shows that large errors occur on images with either a very high or a low root length density. Additionally, a separate model was designed and tested on selected subsets of the data by using a synthetic data generator. Results show that MAE decreases to 10 mm, which is equivalent to 90% accuracy.

Results suggest that this method has great potential to facilitate fully automatic root length measurement on noisy rhizosphere images. Future work will validate the proposed model with a larger datasets comprising of various plant species, soil types and MR imaging systems.

How to cite: soffer, A., Parthasarathi, T., Lasri, A., Hadar, O., Rewald, B., Bodner, G., Baykalov, P., Ephrath, J., and Lazarovitch, N.: Convolutional neural network-based automatic root length measurement in noisy rhizosphere images , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20582, https://doi.org/10.5194/egusphere-egu2020-20582, 2020.

In the past decade, plant root water uptake (RWU) has been a major focus of ecohydrological studies employing water stable isotopes. The interest of the isotopic community for RWU rose concomitantly to the development of open-access multi-source mixing models based on Bayesian inference. Another more general reason was certainly the decrease in analytical cost with the advent of isotope-specific laser absorption spectrometry. The isotopic methodology used to determine relative profiles of RWU works on the premises that (i) RWU does not fractionate stable isotopes in water and (ii) the isotopic composition of water inside the xylem vessel of the last non-evaporating part of the plant (typically the stem) is that of RWU. Following a simple mass balance approach, the isotopic composition of RWU can be linked back by inversion to contributions to RWU (i.e., relative RWU) of a set of potential water sources (of known isotopic compositions) originating from the soil profile.

In recent research, the preferred tool for inverting water isotope data was Bayesian models and the literature shows that only a handful of studies complemented isotope analysis with observation of plant water status and flow. Consequently, most of the gathered information on RWU cannot be used to test hypotheses on which are built physically-based soil-root water flow models. The authors have on the other hand initiated an effort within the framework of dual experimental-modeling approaches, where tightly-controlled experiments are thought and prepared in order to validate, parameterize models, or test hypotheses. The present contribution gives an overview of the different attempts at integrating both water and isotope observations types and confronting them to model simulations explicitly accounting for root system architecture and hydraulic properties. It addresses the meaningfulness and limitations of isotope data, especially in the context of labeling experiments when treated with statistical (e.g. Bayesian) models. We finally propose a way forward and present improvements to be achieved on both experimental and modeling sides to increase the reliability and precision of isotope-derived estimates of RWU.

How to cite: Rothfuss, Y., Couvreur, V., Meunier, F., De Deurwaerder, H., Visser, M. D., and Javaux, M.: Reconstructing Root Water Uptake from isotopic data and physically-based models: looking at recent effort and proposing a path forward, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21157, https://doi.org/10.5194/egusphere-egu2020-21157, 2020.

The study and design of cropping systems that better exploit ecological processes is a priority of the scientific community and intercrops, involving two or more crop species growing simultaneously on the same field, are considered valuable to increase the productivity of traditional family farming and for the sustainable intensification of industrial agriculture.

Advantages of intercrops are based on ecological principles such as diversity, complementarity, facilitation and replacement, which are enhanced in cereal/legume associations because of the differences in the morphology and distribution of the root systems and in the use of different N sources. Understanding the complexity of plant-plant and plant-soil interactions is crucial because beneficial complementarity and facilitation relationships can rapidly turn into negative competition.

The field experiment consisted of a barley (Hordeum vulgare L. subsp. polystichum, var. Jallon) field bean (Vicia faba minor Beck, var. Vesuvio) intercrop (IC) and the respective sole crops (SC) grown at low (0 kg ha^-1) and high (120 kg N ha^-1 and 100 kg P ha^-1) fertilizer inputs. Seed density was100 seeds m^-2 for Fb, 250 seeds m^-2 for B, and 100:125 seeds m^-2 in the Fb:B IC, where plants were arranged in a 1:1 row ratio spaced 15 cm. At barley heading, soil and root samples were collected from the 0-20 cm soil profile and roots were cleaned from the soil with a water flow and then separated by species. Root morphological traits such as length, diameter, surface area and volume were analysed with WinRhizo, then samples were oven dried. On soil samples dehydrogenase, ß-glucosidase, alkaline phosphatase and arylsulphatase activities were determined, and the geometric mean (GMea) of the assayed soil enzyme activities was calculated.

Root density of IC was intermediate between Fb and B SC, the former displaying the highest density on dw basis, the latter on length basis. In both SCs root density was higher without fertilizer input, demonstrating a higher investment in roots in response to NP limitation. In contrast, fertiliser input increased root density in the IC, which we interpreted as a competitive root growth stimulated by the higher nutrient availability in soil.

The specific root length (SRL, m/g) increased in Fb SC in response to NP supply, demonstrating an energy investment in root elongation instead in feeding N₂-fixing bacteria when mineral N was available, which is confirmed by the lower nodule density. The opposite occurred in the B SC, where SRL was reduced by mineral supply. In the IC, NP input increased the SRL of both species, demonstrating strong interspecific competition for nutrient acquisition and not complementarity, as it is generally supposed for cereal/legume intercrops. As a result of the higher investment of resources in root elongation, in Fb, nodule density decreased dramatically. In the fertilized IC soil also the GMea was higher, suggesting a major production of exudates from roots.

How to cite: Cardelli, R., Esnarriaga, D. N. V., Mariotti, M., and Arduini, I.: Root dynamics and soil-enzyme activities in field bean/barley intercrops, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21559, https://doi.org/10.5194/egusphere-egu2020-21559, 2020.