Root hairs bridge the gap between roots and soil water

2020 ◽  
Author(s):  
Patrick Duddek ◽  
Mutez Ahmed ◽  
Mohsen Zarebanadkouki ◽  
Nicolai Koebernick ◽  
Goran Lovric ◽  
...  
Keyword(s):  
Water Uptake ◽  
Contact Area ◽  
Geodesic Distance ◽  
Root Hairs ◽  
Root Water Uptake ◽  
Root Surface ◽  
Particle Packing ◽  
Biophysical Properties ◽  
Soil Matrix ◽  
Water Potentials

<p>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.</p><p>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.</p><p>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.</p><p> </p><p> </p><p>References</p><ul><li>(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.</li> <li>(2) Carminati A, Benard P, Ahmed MA, Zarebanadkouki M. 2017. Liquid bridges at the root-soil interface. Plant and Soil 417, 1–15.</li> </ul><p> </p>

Advances in understanding plant root water uptake

2021 ◽  
pp. 373-392
Author(s):  
Mutez Ali Ahmed ◽  
◽  
Doris Vetterlein ◽  
Andrea Carminati ◽  
◽  
...  
Keyword(s):  
Crop Production ◽  
Plant Root ◽  
Root Hairs ◽  
Water Repellency ◽  
Root Water Uptake ◽  
Root Surface ◽  
Soil Matrix ◽  
Root Shrinkage ◽  
Moisture Conditions ◽  
Rhizosphere Processes

Water deficit is one of the primary limitations to crop production. Here, we review the role of root and rhizosphere hydraulic processes that affect the ability of a plant to extract water from the soil. Prominent features of rhizosphere hydraulic properties are: root shrinkage, alteration of pore geometry in the rhizosphere, effect of mucilage on water retention, hydraulic conductivity and water repellency, root hairs, and mycorrhiza connecting the root surface to the soil matrix. All these factors are strongly dynamic, changing over time and with soil moisture conditions. Although our understanding of the mechanisms related to these factors has advanced significantly in the last ten years, the relative importance of these rhizosphere processes for the ability of crops to extract water from the soil and better tolerate drought is still largely unclear. We propose that the next research step is to investigate the implications of these rhizosphere processes on crop growth and water use economy and use this knowledge to grow more resilient crops that match to their environment.

Mucilage exudation facilitates root water uptake in dry soils

2014 ◽  
Vol 41 (11) ◽  
pp. 1129 ◽  
Author(s):  
Mutez A. Ahmed ◽  
Eva Kroener ◽  
Maire Holz ◽  
Mohsen Zarebanadkouki ◽  
Andrea Carminati
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Root Surface ◽  
Pressure Probe ◽  
Root Pressure ◽  
Plant Trait ◽  
Suction Cup ◽  
Relaxation Curves

As plant roots take up water and the soil dries, water depletion is expected to occur in the rhizosphere. However, recent experiments showed that the rhizosphere was wetter than the bulk soil during root water uptake. We hypothesise that the increased water content in the rhizosphere was caused by mucilage exuded by roots. It is probably that the higher water content in the rhizosphere results in higher hydraulic conductivity of the root–soil interface. In this case, mucilage exudation would favour the uptake of water in dry soils. To test this hypothesis, we covered a suction cup, referred to as an artificial root, with mucilage. We placed it in soil with a water content of 0.03 cm3 cm–3, and used the root pressure probe technique to measure the hydraulic conductivity of the root–soil continuum. The results were compared with measurements with roots not covered with mucilage. The root pressure relaxation curves were fitted with a model of root water uptake including rhizosphere dynamics. The results demonstrated that when mucilage is added to the root surface, it keeps the soil near the roots wet and hydraulically well conductive, facilitating the water flow from dry soils towards the root surface. Mucilage exudation seems to be an optimal plant trait that favours the capture of water when water is scarce.

Impact of soil water potential pattern on root water uptake distribution and leaf water potential

2021 ◽  
Author(s):  
Ali Mehmandoost Kotlar ◽  
Mathieu Javaux
Keyword(s):  
Water Potential ◽  
Root System ◽  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Leaf Water Potential ◽  
Root Water Uptake ◽  
Leaf Water ◽  
Hydraulic Lift ◽  
Water Potentials

<p>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.</p>

Field measured and simulated soil-plant water relations in maize

2021 ◽  
Author(s):  
Helena Jorda Guerra ◽  
Mutez Ahmed ◽  
Anke Coolens ◽  
Mathieu Javaux ◽  
Doris Vetterlein ◽  
...  
Keyword(s):  
Water Stress ◽  
Field Experiment ◽  
Root System ◽  
Soil Water ◽  
Water Uptake ◽  
Water Relations ◽  
Root Hairs ◽  
Root Water Uptake ◽  
Field Scale ◽  
Water Losses

<p>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.</p>

Measuring very negative water potentials with polymer tensiometers: principles, performance and applications

Biologia ◽  
2009 ◽  
Vol 64 (3) ◽  
Author(s):  
Gerrit Rooij ◽  
Martine Ploeg ◽  
Hermanus Gooren ◽  
Gerben Bakker ◽  
Cornelis Hoogendam ◽  
...  
Keyword(s):  
Polymer Solution ◽  
Water Uptake ◽  
Fold Increase ◽  
Root Water Uptake ◽  
Measurement Range ◽  
Water Potentials ◽  
Disturbed Soil ◽  
And Performance ◽  
Wilting Point

AbstractIn recent years, a polymer tensiometer (POT) was developed and tested to directly measure matric potentials in dry soils. By extending the measurement range to wilting point (a 20-fold increase compared to conventional, water-filled tensiometers), a myriad of previously unapproachable research questions are now open to experimental exploration. Furthermore, the instrument may well allow the development of more water-efficient irrigation strategies by recording water potential rather than soil water content. The principle of the sensor is to fill it with a polymer solution instead of water, thereby building up osmotic pressure inside the sensor. A high-quality ceramic allows the exchange of water with the soil while retaining the polymer. The ceramic has pores sufficiently small to remain saturated even under very negative matric potentials. Installing the sensor in an unsaturated soil causes the high pressure of the polymer solution to drop as the water potentials in the soil and in the POT equilibrate. As long as the pressure inside the polymer chamber remains sufficiently large to prevent cavitation, the sensor will function properly. If the osmotic potential in the polymer chamber can produce a pressure of approximately 2.0 MPa when the sensor is placed in water, proper readings down to wilting point are secured. Various tests in disturbed soil, including an experiment with root water uptake, demonstrate the operation and performance of the new polymer tensiometer and illustrate how processes such as root water uptake can be studied in more detail than before. The paper discusses the available data and explores the long term perspectives offered by the instrument.

scholarly journals Simulation of Water and Salt Dynamics in the Soil Profile in the Semi-Arid Region of Tunisia—Evaluation of the Irrigation Method for a Tomato Crop

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1594
Author(s):  
Sabri Kanzari ◽  
Issam Daghari ◽  
Jiří Šimůnek ◽  
Anis Younes ◽  
Riadh Ilahy ◽  
...  
Keyword(s):  
Water Uptake ◽  
Crop Yields ◽  
Root Zone ◽  
Root Water Uptake ◽  
Coefficient Of Determination ◽  
Silty Clay ◽  
Water Requirements ◽  
Tomato Crop ◽  
Soil Matrix ◽  
Irrigation Method

In Tunisia, water used for irrigation is often saline, increasing the risk of salinization for soils and crops. In this study, an experiment was conducted on a tomato crop cultivated on a silty-clay soil irrigated with three different water qualities: 0, 3.5, and 7 dS·m−1. Experimental data were then used to calibrate and validate the Hydrus-1D model, which simulates water flow and salt transfer in soils. The successfully-calibrated and validated model was then used to study the combined effects of the soil osmotic and soil matrix potentials on root water uptake. The values of the root mean square error (RMSE), the coefficient of determination (CD), the modeling efficiency (EF), and the coefficient of residual mass (CRM) were close to their optimal values for both soil water content and soil electrical conductivity profiles, indicating the reliability of the model to reproduce water and salt dynamics. Relative yields (Yr), indirectly estimated using actual and potential root water uptake (transpiration), indicated that the multiplicative stress response model (using the S-shape model) satisfactorily simulates measured yields and reproduces the effects of irrigation with saline waters on crop yields. An alternative scenario using a reduction of water requirements by 50% was investigated to assess an irrigation method with considerable water savings. As the results show that relative yields, Yr, were only slightly reduced, the crop water requirements estimated by CROPWAT 8.0 must have been overestimated. The variation of the soil salinity in the root zone highlighted a high salinization risk in the short-term when water of 7 dS·m−1 is used for irrigation.

Techniques for preparing the Lolium perenne coleorhiza for scanning electron microscope evaluation

1992 ◽  
Vol 50 (1) ◽  
pp. 766-767
Author(s):  
Susan B.G. Debaene ◽  
John S. Gardner ◽  
Phil S. Allen
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Lolium Perenne ◽  
Morphological Study ◽  
Root Hairs ◽  
Inner Pressure ◽  
Water Potentials ◽  
Radicle Emergence ◽  
Standard Fixation ◽  
Scanning Electron

The coleorhiza is a nonvascular sheath that encloses the embryonic radicle in Poaceae, and is generally the first tissue to emerge during germination. Delicate hairlike extensions develop from some coleorhiza cells prior to radicle emergence. Similar to root hairs, coleorhiza hairs are extremely sensitive to desiccation and are damaged by exposure to negative water potentials. The coleorhiza of Lolium perenne is somewhat spherical when first visible, after which a knob forms at a right angle to the caryopsis due to inner pressure from the elongating radicle. This knob increases in length until the radicle finally punctures the coleorhiza. Standard fixation procedures cause severe desiccation of coleorhiza cells and hairs, making morphological study of the coleorhiza difficult. This study was conducted to determine a more successful process for coleorhiza preservation.

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