Root hairs are one root trait among many which enables plants to adapt to environmental conditions. How different traits are coordinated and whether some are mutually exclusive is currently poorly understood. Comparing a root hair defective mutant with its corresponding wild-type we explored if and how the mutant exhibited root growth adaption strategies and as to how far this depended on the substrate.

Zea mays root hair defective mutant (rth3) and the corresponding wild-type siblings were grown on two substrates with contrasting texture and hence nutrient mobility. Root system architecture was investigated over time using repeated X-ray computed tomography.

There was no plastic adaption of root system architecture to the lack of root hairs, which resulted in lower uptake in particular in the substrate with low P mobility. The function of the root hairs for anchoring did not result in different depth profiles of the root length density between genotypes. Both maize genotypes showed a marked response to substrate. This was well reflected in the spatiotemporal development of rhizosphere volume fraction but especially in the strong response of root diameter to substrate, irrespective of genotype.

The most salient root plasticity trait was root diameter in response to substrate, whereas coping mechanisms for missing root hairs were less evident. Further experiments are required to elucidate whether observed differences can be explained by mechanical properties beyond mechanical impedance, root or microbiome ethylene production or differences in diffusion processes within the root or the rhizosphere.

How to cite: Schlüter, S., Lippold, E., Phalempin, M., and Vetterlein, D.: Does the lack of root hairs alter root system architecture of Zea mays?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9710, https://doi.org/10.5194/egusphere-egu21-9710, 2021.

Plant water uptake from soil is an important component of terrestrial water cycle with strong links to the carbon cycle and the land surface energy budget. To simulate the relation between soil water content, root distribution, and root water uptake, models should represent the hydraulics of the soil-root system and describe the flow from the soil towards root segments and within the 3D root system architecture according to hydraulic principles. We have recently demonstrated how macroscopic relations that describe the lumped water uptake by all root segments in a certain soil volume, e.g. in a thin horizontal soil layer in which soil water potentials are uniform, can be derived from the hydraulic properties of the 3D root architecture. The flow equations within the root system can be scaled up exactly and the total root water uptake from a soil volume depends on only two macroscopic characteristics of the root system: the root system conductance, K_rs, and the uptake distribution from the soil when soil water potentials in the soil are uniform, SUF. When a simple root hydraulic architecture was assumed, these two characteristics were sufficient to describe root water uptake from profiles with a non-uniform water distribution. This simplification gave accurate results when root characteristics were calculated directly from the root hydraulic architecture. In a next step, we investigate how the resistance to flow in the soil surrounding the root can be considered in a macroscopic root water uptake model. We specifically investigate whether the macroscopic representation of the flow in the root architecture, which predicts an effective xylem water potential at a certain soil depth, can be coupled with a model that describes the transfer from the soil to the root using a simplified representation of the root distribution in a certain soil layer, i.e. assuming a uniform root distribution.

How to cite: Vanderborght, J., Couvreur, V., Meunier, F., Schnepf, A., Vereecken, H., Bouda, M., and Javaux, M.: Towards the consideration of soil-root resistances in root water uptake models with macroscopic representations of hydraulic root architecture, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8151, https://doi.org/10.5194/egusphere-egu21-8151, 2021.

Mangrove forests are mainly found in the intertidal zone. Their ability to live in saline water enables them to outcompete non-mangrove vegetation in harsh and specific coastal environment. Nevertheless, they can still be invaded by alien mangrove species in suitable hydrological conditions, possibly resulting in more fragile ecosystems. Subtropical mangrove ecosystem demonstrates high variability in mangrove growth and hydrological conditions. However, their interactions are not well-understood, especially for the mangrove interspecific competition in varying groundwater conditions. To address this issue, the present study developed a coupled three-dimensional groundwater-vegetation model based on MANTRA (MANHAM-SUTRA) to simultaneously simulate groundwater hydrodynamics and mangrove distribution. The developed model was then applied to a subtropical mangrove swamp invaded by Sonneratia spp. in Mai Po Nature Reserve, Hong Kong, China. Vegetation domain is updated yearly using the annual mangrove areas extracted from remote-sensing images from 2000 to 2018. Then, multidecadal simulations were performed to validate the model in simulating the interaction between groundwater and mangrove growth. For the piezometric head, all RMS errors are smaller than 0.2 m and the correlation coefficients are larger than 0.86, which proves the effectiveness of the model in groundwater level simulation within Mai Po. The seasonal variations in the groundwater salinity were also well captured in both the fringe forest and the mudflat. The simulated biomass of Sonneratia spp. is mainly distributed at the river outlets, which is also in good agreement with the historical measurements. The validated model can then be used to predict the invasion and the distribution of the exotic mangrove species in the context of future environmental changes for better management of mangrove swamps. Since Sonneratia is a common alien species in southern China, the model can also be used for regional management of mangrove invasion and conservation of native species. The insights obtained from this study may also provide references for other similar studies examining the interaction between coastal groundwater and vegetation.

How to cite: Luo, S. and Chui, T. F. M.: Development of a Coupled 3D Groundwater-Vegetation Model for Coastal Wetlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4101, https://doi.org/10.5194/egusphere-egu21-4101, 2021.

Soil-plant-atmosphere interactions are studied to improve the estimation of actual transpiration – the key part of the catchment water balance. The one-dimensional soil water flow model S1D, involving vertically distributed macroscopic root water uptake and whole-plant hydraulic capacitance, was used. The model is based on the numerical solution of Richards' equation coupled with a transient transpiration stream algorithm.

The study focuses on the catchment Liz located in the Bohemian Forest, Czech Republic. The catchment is covered with Norway spruce (Picea abies) and European beech (Fagus sylvatica). In 2020, sap flow measurements by thermal dissipation probes were conducted at both forest environments. Soil water pressure head, soil water content, and soil temperature data, as well as complete meteorological data from the nearby meteorological station, were also available for the whole period of interest.

The registered sap flow and simulated transpiration fluxes are compared with a particular attention to the different behavior of isohydric (spruce) and anisohydric (beech) trees. The model reasonably well reproduces the plant responses caused by both the high midday potential transpiration demand and the occasional soil drought.

The research is supported by the Czech Science Foundation Project No. 20-00788S.

How to cite: Skalova, V., Dohnal, M., Votrubova, J., Vogel, T., and Tesar, M.: Modeling of plant water uptake in two distinct forest stands using whole-plant capacitance approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2579, https://doi.org/10.5194/egusphere-egu21-2579, 2021.

The fundamental question as to what triggers stomatal closure during soil drying remains contentious. Thus, we urgently need to improve our understanding of stomatal response to water deficits in soil and atmosphere. Here, we investigated the role of soil-plant hydraulic conductance (K_sp) on transpiration (E) and stomata regulation. We used a root pressure chamber to measure the relation between E, leaf xylem water potential (ψ_leaf-x) and soil water potential (ψ_soil) in tomato. Additional measurements of ψ_leaf-x were performed with unpressurized plants. A soil-plant hydraulic model was used to simulate E(ψ_leaf-x) for decreasing ψ_soil. In wet soils, E(ψ_leaf-x) had a constant slope while in dry soils the slope decreased, with ψ_leaf-x rapidly and nonlinearly decreasing for moderate increases in E. The ψ_leaf-x measured in pressurized and unpressurized plants matched well, which indicates that the shoot hydraulic conductance did not decrease during soil drying and that the decrease in K_sp is caused by a decrease in soil-root conductance. The decrease of E matched well the onset of hydraulic nonlinearity. Our findings demonstrate that stomatal closure prevents the drop in ψ_leaf-x caused by a decrease in K_sp and elucidate a strong correlation between stomatal regulation and belowground hydraulic limitation.

How to cite: Abdalla, M., Carminati, A., Cai, G., Javaux, M., and Ahmed, M.: Declining soil-root hydraulic conductance drives stomatal closure of tomato under drought , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4192, https://doi.org/10.5194/egusphere-egu21-4192, 2021.

Guttation is the exudation of xylem sap from vascular plant leaves. This process is particularly interesting because in its configuration root water uptake occurs against the hydrostatic pressure driving force. Hence, it emphasizes the contribution of another driving force that lifts water in plants: the osmotic potential gradient.

The current paradigm of root water uptake explains that, due to the endodermal apoplastic barrier, water flows across root radius from the same principles as through selective membranes: driven by the total water potential gradient. This theory relies on the idea that during guttation, osmolites loaded in xylem vessels decrease xylem total water potential, making it more negative than the total soil water potential, and generating water inflow by osmosis as in an osmometer.

However, this theory fails at explaining experiments in which guttation occurs without sufficient solute loading in root xylem of maize (Enns et al., 1998; Enns et al., 2000) and arrowleaf saltbush (Bai et al., 2007) among others; studies concluding that experimental observations “could not be explained with the current theories in plant physiology”. Such flow rates towards combined increasing pressure potentials and increasing osmotic potentials between separate apoplastic compartments would necessitate an effective root radial conductivity that is negative; a mind bender.

What piece of hydraulic network would make it possible for water to flow against the total water potential driving force?

We implemented Steudle’s composite water transport model in the explicit root cross-section anatomical hydraulic network MECHA (Couvreur et al., 2018). All apoplastic, transmembrane and symplastic pathways are interconnected in the network. The results show that while root radial conductivity is particularly sensitive to cell membrane permeability, the combination of conductive plasmodesmata and increased dilution of protoplast osmotic potentials inwards is a key to explain root water flow towards increasing total potentials. A triple cell theory is suggested as new paradigm of root radial flow.

References

Bai X-F, Zhu J-J, Zhang P, Wang Y-H, Yang L-Q, Zhang L (2007) Na+ and Water Uptake in Relation to the Radial Reflection Coefficient of Root in Arrowleaf Saltbush Under Salt Stress. Journal of Integrative Plant Biology 49: 1334-1340

Couvreur V, Faget M, Lobet G, Javaux M, Chaumont F, Draye X (2018) Going with the Flow: Multiscale Insights into the Composite Nature of Water Transport in Roots. Plant Physiology 178: 1689-1703

Enns LC, Canny MJ, McCully ME (2000) An investigation of the role of solutes in the xylem sap and in the xylem parenchyma as the source of root pressure. Protoplasma 211: 183-197

Enns LC, McCully ME, Canny MJ (1998) Solute concentrations in xylem sap along vessels of maize primary roots at high root pressure. J. Exp. Bot. 49: 1539-1544

How to cite: Couvreur, V., Heymans, A., Lobet, G., Bennett, M., and Draye, X.: The plant water pump: why water flows uphill of water potential gradients in a root hydraulic anatomy model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14006, https://doi.org/10.5194/egusphere-egu21-14006, 2021.

Root water uptake is a major process controlling water balance and accounts for about 60% of global terrestrial evapotranspiration. The root system employs different strategies to better exploit available soil water, however, the regulation of water uptake under the spatiotemporal heterogeneous and uneven distribution of soil water is still a major question. To tackle this question, we need to understand how plants cope with this heterogeneity by adjustment of above ground responses to partial rhizosphere drying. Therefore, we use R-SWMS simulating soil water flow, flow towards the roots, and radial and the axial flow inside the root system to perform numerical experiments on a 9-cell gridded rhizotrone (50 cm×50 cm). The water potentials in each cell can be varied and fixed for the period of simulation and no water flow is allowed between cells while roots can pass over the boundaries. Then a static mature maize root architecture to different extents invaded in all cells is subjected to the various arrangements of cells' soil water potentials. R-SWMS allows determining possible hydraulic lift in drier areas. With these simulations, the variation of root water and leaf water potential will be determined and the role of root length density in each cell and corresponding average soil-root water potential will be statistically discussed.

How to cite: Mehmandoost Kotlar, A. and Javaux, M.: Impact of soil water potential pattern on root water uptake distribution and leaf water potential, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15095, https://doi.org/10.5194/egusphere-egu21-15095, 2021.

Recent advances in scaling up water flows on root system networks hold promise for improving predictions of water uptake at large scales. These developments are particularly timely, as persistent difficulties in getting Earth system models to accurately represent soil-root water flows, especially under drying or heterogeneous soil moisture conditions, are now a major obstacle describing the water limitation of terrestrial fluxes.

One recently developed upscaling formalism has been shown to be both free of discretisation error in flow predictions regardless of scale and with computational cost linearly diminishing with the number of soil subdomains considered. What has been missing from this approach, however, is a proven method to apply it generally – i.e. to an arbitrary root system architecture discretised on an arbitrary grid.

The work presented here demonstrates a general algorithm that can be applied to a wide range of root system architectures (the only assumption being that only one lateral root originates at one point along a parent root) discretised on a grid consisting of a series of soil layers of variable thickness, as is common in Earth system models. It is further shown theoretically that both of these restrictions can in principle be relaxed and that this approach can in principle be extended to conditions of soil moisture heterogeneity – i.e. situations where each root segment in a soil grid cell faces a different water potential at the soil-root interface.

This work represents both a practical advance bringing broad applicability to this upscaling approach and a major theoretical advance as exact solutions for water uptake under conditions of soil moisture heterogeneity within grid cells were previously unknown. While obtaining exact solutions despite heterogeneity within the grid cell requires a way of finding the overall mean soil water potential faced by the plant, this advance nevertheless points to possible directions of future research for overcoming the major hurdle of soil moisture heterogeneity.

How to cite: Bouda, M., Vanderborght, J., and Javaux, M.: A general approach for analytically upscaling the exact root water uptake equations despite heterogeneous soil moisture at the soil-root interface, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13601, https://doi.org/10.5194/egusphere-egu21-13601, 2021.

The surface tension (ST) of xylem sap at the water-air interface is a crucial phenomenon, influencing many physiological events such as air seeding and embolism, by which xylem vessels become air-filled and cease to function. Refilling of embolized, may relies on sap’s surface activity at the interface. It is commonly assumed that the ST of xylem sap is equal to the ST of pure water (72 mN/m). However, xylem sap is a complex solution and consists of surface-active molecules that may adsorb and accumulate at the water-air interface and thereby reduce the ST of water as a function of their aqueous concentration. However, when a new water-air interface is formed, equilibrium ST is not reached instantaneously. Specifically, amphiphilic molecules are kinetically adsorbed and undergo orientation at the interface following diffusion from the bulk solution. Dynamic ST of xylem sap and liquid-solid interactions, describing the surface phenomena of the xylem of vascular plants is currently not fully understood. This is mainly due to a lack of quantitative knowledge on the rate and extent of dynamic and equilibrium ST of sap. In this regard, the main objective of this study is to quantify the dynamic and equilibrium ST of xylem sap as a function of their aqueous concentration. We extracted xylem sap from lemon trees and measured ST as a function of time using the pendant drop technique. The dynamic ST data were analyzed using empirical and diffusion-control mathematical models which adequately described the exponential-like decay of the ST as a function of time. The results showed reduced ST of water in the xylem sap, indicating significant surface activity, reaching equilibrium ST values as low as 42 mN/m. The rate of ST decay was higher in high sap concentration and reduced in diluted one. The results of dynamic and equilibrium ST and the corresponding model will be presented and their implications for xylem hydraulic functioning will be discussed.

Keywords: Dynamic surface tension, Equilibrium surface tension, Diffusion, Xylem sap.

How to cite: Duggireddy, R. P., Raveh, E., and Arye, G.: Dynamic surface tension of xylem sap at the air-water interface, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10851, https://doi.org/10.5194/egusphere-egu21-10851, 2021.

Climate models predict hotter and dryer summers in Germany, with longer periods of extreme droughts like in summer 2018. How does this affect the water uptake and transport in tree roots growing in the top- and subsoil?

In summer 2018 and 2019 we measured the water transport in fine roots (<5mm) of European Beech on tertiary sand and triassic sandstone up to 2 m depth. We adapted the well-established HRM technique to enable measurements of very small sap flow rates in small roots. Thus, we measured the water transport as a temperature ratio of a stretching heat pulse.

Relating sap flow to root surface area, root depth, anatomy, soil moisture, and VPD allows for interesting insights in tree water uptake rates: Where are the limits of drought intensity and duration, for water uptake and recovery of small roots? Are there differences in the function of top- and subsoil roots? Are roots specialized for water transport or nutrient uptake? The investigated data gives a first hint on how the water transport in Beech roots differs with changes in the soil moisture and VPD under changing climate.

How to cite: Messinger, E., Coners, H., Hertel, D., and Leuschner, C.: Water transport in European Beech roots (<5mm) under drought in the south of Lower Saxony , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2859, https://doi.org/10.5194/egusphere-egu21-2859, 2021.

Root hairs represent an attractive target for future crop breeding, to improve resource use efficiency and stress tolerance. Most studies investigating root hairs have focused on plant tolerance to phosphorus deficiency and rhizosheath formation under controlled conditions. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. Although root hairs and rhizosphere are assumed to play a key role in regulating plant water relations, their effect on plant water uptake has been rarely investigated. As such, this study aimed to experimentally elucidate some of the impacts that root hairs have on plant performance under field conditions and water deficit. A field experiment was set up in Scotland for two consecutive years, in 2017 (a typical year) and 2018 (the driest growing season ever recorded at this site), under different soil textures (i.e., clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance. This resulted in less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot phosphorus accumulation. Specifically, minimum leaf water potential differed significantly (P = 0.021) between the wild type (-1.43 MPa) and its hairless mutant (-1.76 MPa) grown in clay loam, with the mutant exhibiting greater water stress. In agreement with leaf water potential measurements, at the peak of water stress, leaf abscisic acid concentration was significantly (P = 0.023) greater for the hairless mutant (394 ng g^-1) than the wild type (250 ng g^-1) grown in clay loam soil. Under water deficit conditions, in clay loam soil, shoot phosphorus accumulation in the wild type (2.49 mg P shoot^-1) was over twice that in the hairless mutant (1.10 mg P shoot^-1). Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. While yield of the hairless mutant significantly (P = 0.012) decreased from 2017 to 2018 in both clay (-26%) and sandy (-33%) loam soils, no significant differences were found between years in the yield of the wild type. Therefore, selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder’s dilemma of trying to simultaneously enhance both productivity and resilience. To our knowledge, the present findings provide the first evidence of the effect of root hairs under drought in open field conditions (i.e., real agricultural system). Therefore, along with the well-recognized role for P uptake, maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change.

How to cite: Marin, M., Feeney, D. S., Brown, L. K., Naveed, M., Ruiz, S., Koebernick, N., Bengough, A. G., Hallett, P. D., Roose, T., Puértolas, J., Dodd, I. C., and George, T. S.: The effect of root hairs under drought in open field conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6332, https://doi.org/10.5194/egusphere-egu21-6332, 2021.

Background - Plants grow complex root architectures to explore the soil volume and acquire water and nutrients. The growth of root systems affects the hydraulic properties of soil, and experimental investigations suggest that the hydraulic conductivity is significantly increased in vegetated soil with in comparison to a fallow soil. The mechanisms through which this occurs are not well characterised.

Material and Methods - In this work we propose a novel model for moisture transport through vegetated soil. The model reflects the hypothesis that water flow is a function of the direction of an incumbent root structure, and we use data from constant-head infiltration assays [1] to test hypotheses on the nature of water transport in the soil adjacent to plant roots.

Results - Results suggest that differences in hydraulic conductivity between vegetated and fallow soil may be due to preferential flow of moisture in the direction of plant roots.

Conclusion – The research therefore, confirms that root architectural parameters may play a determinant role in predicting water infiltration of vegetated soil. This could open new avenues of research to improve prediction and management of irrigation and flood defence.

 [1] Leung, A. K., Boldrin, D., Liang, T., Wu, Z. Y., Kamchoom, V., & Bengough, A. G. (2018). Plant age effects on soil infiltration rate during early plant establishment. Géotechnique, 68(7), 646-652.

Figure 1 Simulation of water infiltration in vegetated and non-vegetated soil. (A) Simulated root system. (B) Construction of oriented root volumetric density used for computation of facilitated transport. (C) Water fluxes within the root system. (D) Water fluxes in fallow soil.

How to cite: Mair, A., Dupuy, L., and Ptashnyk, M.: Models of facilitated transport of soil moisture through root systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16354, https://doi.org/10.5194/egusphere-egu21-16354, 2021.

1D-3D methods are used to describe root water and nutrient uptake in complex root networks. Root systems are described as networks of line segments embedded in a three-dimensional soil domain. Particularly for dry soils, local water pressure and nutrient concentration gradients can be become very large in the vicinity of roots. Commonly used discretization lengths (for example 1cm) in root-soil interaction models do not allow to capture these gradients accurately. We present a new numerical scheme for approximating root-soil interface fluxes. The scheme is formulated in the continuous PDE setting so that is it formally independent of the spatial discretization scheme (e.g. FVM, FD, FEM). The interface flux approximation is based on a reconstruction of interface quantities using local analytical solutions of the steady-rate Richards equation. The local mass exchange is numerically distributed in the vicinity of the root. The distribution results in a regularization of the soil pressure solution which is easier to approximate numerically. This technique allows for coarser grid resolutions while maintaining approximation accuracy. The new scheme is verified numerically against analytical solutions for simplified cases. We also explore limitations and possible errors in the flux approximation with numerical test cases. Finally, we present the results of a recently published benchmark case using this new method.

How to cite: Koch, T., Wu, H., Mardal, K.-A., Helmig, R., and Schneider, M.: A new numerical method to approximate root water uptake fluxes in a mixed-dimensional 1D-3D setting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-390, https://doi.org/10.5194/egusphere-egu21-390, 2020.

The distribution of nutrients in the soil is very heterogeneous at different scales relevant to plant roots, and plants respond to this heterogeneity by the architecture of the root system. The ability to form the root system in terms of the most effective nutrient uptake differs among species. Moreover, over 70% of terrestrial plants create arbuscular mycorrhizal symbiosis, which helps them to acquire nutrients from the soil. It has been shown that plants with mycorrhizal symbiosis acquire nutrients from heterogeneous soil differently than plants without mycorrhizal fungi. Our study aims to estimate the link between the root and fungal foraging for heterogeneous sources using an experimental approach. We show the root foraging precision of nine plant species together with three fungal species in the heterogeneous soil environment. The first results suggest that root foraging is not affected by the presence of mycorrhizal fungi and that fungal foraging may form in the opposite direction than root foraging.

How to cite: Stiblíková, P., Weiser, M., and Jansa, J.: The root-fungus interplay in foraging for heterogeneous sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7796, https://doi.org/10.5194/egusphere-egu21-7796, 2021.

Reducing nitrate leaching from agricultural land to aquifers is a high priority concern for more than a half a century. Theory and observations of a threshold concentration of nitrate in the root-zone (Cmax), from which the leachate concentration increases at higher rates with increasing root-zone nitrate concentration, are presented. Cmax is derived both by direct results from container experiments with varying nitrogen (N) fertigation, and as calibration parameter in N-transport models beneath commercial agricultural plots. For five different crops, Cmax ranged between 20-45 mg/l of NO₃-N derived from experiments and models. However, for lettuce, which was irrigated with a large leaching fraction, a Cmax could not be defined. For the crops irrigated and fertilized in the warm/dry season (corn and citrus) experiments show a dramatic change in leachate concentrations and simulations reveal a wide range of sensitivity of leachate NO₃-N concentration to Cmax. Annual crops that are irrigated and fertilized in the cool/wet season (e.g. potato in Mediterranean climate) showed a distinct Cmax yet less dramatic than the summer-irrigated crops in the container experiment, and smaller impact of Cmax in models. Simulations showed that for summer-irrigated crops maintaining fertigation at C<Cmax has a significant effect on deep leachate concentrations, whereas for the winter annual crops the simulations revealed no threshold. It is suggested that for summer-irrigated crops fertigation below Cmax robustly serves the co-sustainability of intensive agriculture and aquifer water quality, for the winter crops it is suggested but benefits are not robust. For short season, small root-system crops (lettuce) efforts should be made to detach the crop from the soil.

How to cite: Kurtzman, D., Kanner, B., Levy, Y., Nitsan, I., and Bar-Tal, A.: Reducing leaching using the threshold nitrate root-uptake phenomena, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8780, https://doi.org/10.5194/egusphere-egu21-8780, 2021.

A main problem currently facing agriculture is drought. More frequent and longer drought periods are predicted to threaten agricultural yields in future. The capacity of soils to hold water is a highly important factor controlling drought stress intensity for plants during the growing phase. Amorphous silica (ASi) has been suggested to be able to mitigate these problems. Amorphous silica pools in natural soils are in the range of 0-6%. However, ASi pools have declined in agricultural soils since the development of high intensity agriculture to values of <1% due to yearly crop harvests, decreasing the water holding capacity of the soils. Here, we analyzed the effect of ASi on the water holding capacity (WHC) of soils. ASi was mixed at varying rates with different soils. Afterwards, the retention curve of the soils was determined. Here we show that ASi increases the soil water holding capacity substantially, by forming silica gels with a water content at soil saturation higher than 700%. An increase of ASi by 1% or 5% (weight) increased the water content at all studied water potentials and plant available water increased by >40% and >60%, respectively. In a lysimeter experiment we found that ASi strongly increased the WHC of soils, too. In a field experiment we found an increase of soil moisture after ASi fertilization over the whole growing season. Furthermore, wheat plant grown in this field experiment suffered less from drought and had a later onset of senescence. Our results suggest that ASi is a main control on soil water availability, potentially decreases drought stress for plants in future.

How to cite: Schaller, J.: Amorphous silica increases the water holding capacity of soils – from mechanistic understanding to field experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-663, https://doi.org/10.5194/egusphere-egu21-663, 2021.

Root exudates affect the physical properties of the rhizosphere, but how these changes affect its solute transport properties is unknown. Understanding how exudates affect the rhizosphere’s transport properties could advance the knowledge on nutrient dynamics in soil and its availability to plants. In the current study, we tested the effects of two exudates (chia mucilage and wheat root exudates) on the transport of iodide and potassium in soil. Solute breakthrough experiments, conducted in saturated loamy sand or coarser textured quartz sand, revealed that increasing the exudate concentration in soil results in increasingly non-equilibrium transport of both solutes. This was demonstrated by an initial solute breakthrough at a lower pore volume, followed by the arrival of the peak solute concentration at a higher pore volume. These patterns were more pronounced in soil mixed with mucilage, and in the quartz sand. An equilibrium or a physical non-equilibrium mobile-immobile transport model, fitted to the measured results, indicated an increase in the fraction of immobile water when increasing the exudates’ concentration in soil. For example, the estimated fraction of immobile water was up from 0 in quartz sand without exudates to 0.75 at a mucilage concentration of 0.2% in quartz sand. The solutes’ breakthrough under variably saturated conditions was also altered by the exudates, demonstrated by higher amounts of the solutes measured per volume of water extracted from soil mixed with exudates, compared to soil without exudates. The results indicate that exudates have a major effect on the rhizosphere’s transport properties, most likely since in its presence low-conducting flow paths are formed, resulting in a physical non-equilibrium during solute transport.

How to cite: Paporisch, A., Harel Bavli, H., Strickman, R., Neuman, R., and Schwartz, N.: Root Exudates Alters Nutrient Transport in Soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6586, https://doi.org/10.5194/egusphere-egu21-6586, 2021.

Sustaining world food production under a changing climate and a growing population demands for higher optimization of agricultural resources including water. This requires an accurate understanding and prediction of root water uptake from soils, which depends on several root traits. The role of root hairs in root water uptake is still under debate, with experimental data that both prove and reject the hypothesis that root hairs can facilitate root water uptake, especially under drought conditions. Our objective was to investigate the effect of root hairs in maize at the field scale. A wildtype maize variety (with root hairs) and a hairless mutant were grown in two substrates (loam and sand) at a field site near Halle, Germany (Vetterlein et al., 2020, JPLN). Transpiration, leaf water potential, soil water content and potentials were monitored during 2019 and 2020. Root length density and leaf area were measured at four different plant development stages. A version of Hydrus 1D coupled with Couvreur’s macroscopic root water uptake model (Couvreur et al., 2012, HESS) was parameterized and used to further investigate soil-water relations in this field experiment. In both years, plants emptied the available water in the profile by July, and relied on rain and irrigation afterwards. Non-significant differences in cumulative water losses from the soil, estimated from soil water content measurements, were observed among the four treatments in both years. These results are in agreement with simulated water losses, which also showed small differences in cumulative transpiration among treatments. Mutant plants developed significantly smaller shoots while transpiring similar water volumes as wildtype plants, indicating lower water use efficiency. While there was no visible effect of the genotype in the soil-water relations, a clear effect of the soil type was observed. Simulated collar water potentials and field observations of rolled leaves indicated water stress occurred first in the loam compared to the sand treatments. Plants grew faster in the loam, leading to earlier onset of water stress. Even though plants in the loam produced less roots than in the sand, the onset of stress was not caused by the smaller root system since simulations presuming a larger root system did not predict a later onset of stress. Similarly, a simulation run using a smaller root system in the sandy soil did not predict a significantly earlier onset of stress. Finally, although our model simulations considered only differences in root density among treatments and did not consider different root or rhizosphere properties of the different soils and genotypes, it simulated the observed water dynamics well. Water depletion in the loamy soil was simulated earlier than it was measured. We hypothesize that this is caused by changing root hydraulic properties when roots develop and mature, and suggest that young roots do not start taking up water immediately. Nevertheless, the data quantity and quality obtained in this field experiment exposes the difficulties and challenges we face to monitor water potentials and fluxes in the soil-plant continuum in annual grasses at the field scale.

How to cite: Jorda Guerra, H., Ahmed, M., Coolens, A., Javaux, M., Vetterlein, D., and Vanderborght, J.: Field measured and simulated soil-plant water relations in maize, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15662, https://doi.org/10.5194/egusphere-egu21-15662, 2021.

Plant roots are able to exude vast amounts of metabolites into the rhizosphere especially when subjected to phosphorus (P) deficiency to increase P solubility and thus its´ uptake. This causes noteworthy costs in terms of energy and carbon (C) for the plants. For this reason, we suggested that exudates reacquisition by roots could represent an energy saving strategy of plants. This study aimed at investigating the effect of P deficiency on the ability of hydroponically grown tomato plants to re-uptake specific metabolites generally present in root exudates by using ¹³C-labelled molecules. Hence, tomato plants have been grown for 21 days in full and P deficient nutrient solution. Exudates reuptake has been assessed by immersion of roots in a solution containing ¹³C labeled glycine, glucose, fructose, citrate, and malate. δ¹³C analysis was performed using a Continuous Flow Isotope Ratio Mass Spectrometer (CFIRMS). Results revealed that P deficient tomato plants were able to take up significantly more citrate (+37%) and malate (+37%), when compared to controls. While also glycine (+42%) and fructose (+49%) uptake was enhanced in P shortage, glucose acquisition was not affected by plants nutritional status. Unexpectedly, results also highlighted that P deficiency leads to a ¹³C enrichment in both tomato roots and shoots over time (shoots +2.66 ‰, roots +2.64 ‰, compared to control plants). This could be explained by stomata closure triggered by P deficiency resulting in an increased use of ¹³CO₂ in respect to ¹²CO₂, normally preferred by RuBisCO. Our findings highlight that tomato plants are able to take up a wide range of metabolites belonging to root exudates, thus optimizing C trade off. This trait is particularly evident when plants grew in P deficiency.

How to cite: Tiziani, R., Trevisan, F., Pii, Y., Celletti, S., Cesco, S., and Mimmo, T.: Tomato plants reuptake root exudates and alter carbon isotope fractionation under phosphorus deficiency, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9459, https://doi.org/10.5194/egusphere-egu21-9459, 2021.

The importance of rock particle size to localized plant species distribution in subnival habitats of the Central Great Caucasus Mountains

Tamar Jolokhava^1,2,5*, Otar Abdaladze² , Zezva Asanidze^2,4 and Zaal Kikvidze ^3,4

Faculty of Exact and Natural Sciences, Ivane Javakhishvili Tbilisi State University, Georgia¹

School of Natural Sciences and Medicine, Institute of Ecology, Ilia State University, Georgia ²

Institute of Ethnobiology and Socio-ecology, Ilia State University, Georgia ³

Institute of Botany, Ilia State University, Georgia ⁴

Ministry of Environmental Protection and Agriculture of Georgia, Science-Research Centre of Agriculture, Soil Fertility Division, Georgia⁵

Subnival habitats of the Central Caucasus represent typical rocky environments with very sparse soil cover and patchy vegetation. We studied how plant species spatial distribution in a subnival habitat (alpine-nival ecotone) depends on the size of rock particles. As a first step we described the climate (mean air temperature and annual precipitation) at two sampling areas, Mt. Tetnuldi (43°01′49.9″N, 42°55′36.0″E) and Mt. Kazbegi (42°39′46.87″N; 44°33′12.87″E), at elevations of 3000 to 3100 m a. s. l. The major climatic characteristics of these two sampling areas were similar and the minor differences in them should not affect measurably the relationships between substrate coarse fragments and plant species distributions.

We categorized rock particles in following size classes (soil; 0.2-0.6cm; 0.6-2cm; 2-6cm; 6-20cm; 20-60cm).We found that large-sized rock particles (6-20cm; 20-60cm) prevailed on the surface, the largest class of 20-60cm was in a strong negative correlation with smaller classes (0.2-0.6cm, 0.6-2cm and 2-6cm), but correlation was insignificant between the large fragments(classes of 6-20cm and 20-60cm) and the soil.

We also examined how plant species associated with the rock particles of different sizes using Canonical Correspondence Analysis (CCA). Overall, we recorded 58 species, out of which 31 species were frequent (>10) and were used in the CCA. Some plant species showed a clear preference to large rock fragments while other associated clearly with soil; in particular, Tephroseris karjaginii, Ziziphora puschkinii, Festuca supina, Minuartia inamoena and Saxifraga juniperifolia tended to colonise a substrate with large fragments (20-60cm), Senecio sosnowskyi and Ziziphora subnivalis showed certain affinity to rock fragment size of 6-20cm, while Carex tristis and Sibbaldia parviflorum prefered soil substratum. We found that, while large-sized rock particles (6-20cm; 20-60cm) prevailed on the surface, most plants were associated with relatively rare fine-grained substrata and, to a lesser extent, with even rarer soil-covered spots. Our results show that the differential preference of species for certain sizes of rock particles observed in our study can conform well to the patchy pattern of vegetation typical for subnival habitats: many species that prefer a fine-grained substratum might clump together at such fine-grained spots and form the patches of associated plants provided there are facilitative interactions among them; the species that prefer coarser-grained substrata might establish as solitary plants outside of the patches.

How to cite: Jolokhava, T., Abdaladze, O., Asanidze, Z., and Kikvidze, Z.: The importance of rock particle size to localized plant species distribution in subnival habitats of the Central Great Caucasus Mountains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-294, https://doi.org/10.5194/egusphere-egu21-294, 2020.

EMF play an important role in forests around the globe, by improving tree nutrition and water supply, as well as connecting different tree species through common mycorrhizal networks (CMN's). However, the extent to which EMF control resource sharing within these networks has not yet been thoroughly addressed. We constructed a simple network of tree-fungus-tree and monitored carbon flow from a ¹³CO₂ labeled donor tree to the final recipient.  DNA Stable Isotope Probing (DNA-SIP) of ectomycorrhizal root tips was used to identify the main fungal symbionts involved in carbon transfer among trees. We used pairs of inter and intra-specie Pinus halepensis and Quercus calliprinos saplings, and examined the carbon dynamics for 40 days within the leaf, stem and root tissues. The peak of ¹³C in the roots of the donor trees was around day 4 post labeling, while the recipient roots peaked at day 9 with observed differences between pairs. The intrinsic tree carbon pool, and not the tree species identity, was the main factor governing carbon transfer between trees. Finally, we were able to identify the main fungal symbionts enriched with ¹³C. Our results add the "missing piece of the puzzle" by linking specific mycorrhizal species to carbon transfer within CMN's.

How to cite: Livne- Luzon, S., Cahanovitc, R., and Klein, T.: Shooting the messenger: Identifying the mycorrhizal species transferring carbon between neighboring trees, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10644, https://doi.org/10.5194/egusphere-egu21-10644, 2021.

Shelterbelts, also termed windbreaks, play a significant role in reducing soil erosion, sand drift, and protecting crops, livestock and farmstead. Cropland shelterbelts are known to improve the microclimate and provide protection against sand-related damages to crops. However, the protection of shelterbelts to crops may be complicated by fine roots near the edge of the shelterbelt, which directly affects the absorption of soil water and the accumulation of soil organic carbon. In this study, we investigated the effects of shelterbelt fine roots on farmland soil water content (SWC) and soil organic carbon density in an agricultural system located in northern China. The distribution characteristics of fine-root biomass density, soil water content and soil organic carbon density were measured at the 0-200 cm soil depth in a farmland shelterbelt system at distances of 0.3H (H is the windbreak height), 0.5H, and 0.7H from the shelterbelt with three replicates. Soil samples were randomly collected in the center of the cropland. The results showed that fine roots of shelterbelts concentrated at the depth of the 20-60 cm soil layer, whereas the fine roots of the crop summer squash (Cucurbita pepo L.) were mainly found within the top 20 cm of the soil profile. With the presence of shelterbelt fine roots, strong SWC deficiency that occurred up to100 cm in the soil profile was observed. The SWC was deficient at all sampling points, the overall shallow layer deficient was larger than the deep layer. In contrast, the soil organic carbon was cumulative, and the overall deep accumulation was greater than the shallow layer. The effects of fine roots on SWC and soil organic carbon density variations in different soil layers were inconsistent. The information accrued in this study can be used to evaluate the effect of farmland shelterbelt on soil water and soil carbon in the Hetao irrigation area of Inner Mongolia, northern China.

How to cite: Xiao, H., Li, J., Xin, Z., Wang, G., and Wang, D.: Effects of fine roots on the distribution of soil water and soil organic carbon in a shelterbelt modified agricultural system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16234, https://doi.org/10.5194/egusphere-egu21-16234, 2021.

Plant species differ in their ability to preferentially grow their roots into nutrient-rich patches in the substrate - this aspect of plant phenotypic plasticity is known as "root foraging". Using a set of approx. 80 Central European herbaceous species of open habitats we show how the root foraging precision of the species is linked to their usual environment. We have obtained the root foraging data experimentally and we combine them with tabelar data that describe species' preference for soil moisture and soil nutrients availability (Ellenberg's Indicator Values), species' ability to occupy frequently disturbed habitats and typical habitats of the species in general. 

How to cite: Weiser, M., Koubek, T., and Herben, T.: Where do the good foragers live?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13559, https://doi.org/10.5194/egusphere-egu21-13559, 2021.

Container size and fruit load intensity are two common factors manipulated to regulate plant growth and development. As saline water is increasingly used for irrigation in arid and semi-arid regions, it is important to study effects of container size and fruit load intensity on tomato in both aboveground and belowground parts under salt stress. The experiment was conducted in a net house located in Sede Boqer Campus, Israel. Containers of four sizes (8-, 28-, 48-, and 200L with the same depth but vary in diameters), two salinity levels (1.5- and 7.5 dS m⁻¹) and two crop load intensities (0% and 100%) were applied. Gas exchange parameters (i.e., stomatal conductance and CO₂ assimilation rate), plant growth parameters (i.e., plant height and stem diameter), and root development were monitored periodically. Plant biomass and various root traits were measured at harvest. For aboveground part, results revealed that container size and salinity level significantly influenced gas exchange performance while fruit load intensity had no significant effect. Plants grown in larger containers without salt stress had higher stomatal conductance and CO₂ assimilation rate. Plant height and stem diameter were significantly greater in plants grown in 200L than those in other containers despite salinity and fruit load levels. Moreover, plants grown in 200L containers exhibited significant increase of 56.3%, 152.9%, and 174.9% respectively in yield compared with those grown in 48-, 28- and 8L under salt stress. The increase magnitudes were greater when there was no salt stress: 109.0%, 430.8%, and 454.0% respectively. For belowground parts, increased container size leads to increased rooting depth. Besides, Minirhizotron data showed that in 200L containers, plants grown under low salinity without fruit developed the greatest total root length. More detailed root data will be presented.  It is concluded that container size has a pronounced effect on physiological behaviours of tomato plants. Therefore, properly increasing container size can alleviate yield reduction under saline irrigation.

How to cite: Zhou, K., Lazarovitch, N., and Ephrath, J.: Effects of container size and fruit load intensity on tomato under salt stress, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1960, https://doi.org/10.5194/egusphere-egu21-1960, 2021.