Root hairs enable high transpiration rates in drying soils

Carminati, Andrea; Passioura, J. B.; Zarebanadkouki, Mohsen; Ahmed, Mutez Ali; Ryan, Peter R.; Watt, Michelle; Delhaize, Emmanuel

doi:10.1111/nph.14715

Cited by 128 publications

(135 citation statements)

References 47 publications

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“…Eventually, when plants are exposed to severe drying, their roots shrink and lose part of their contact to the soil (Carminati et al, 2013), which further decreases the conductance between rhizosphere and root. On the other hand, plants can close this gap and attenuate the drop in conductivity by secreting mucilage (Carminati et al, 2010) or by growing root hairs (Carminati et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Transpiration Reduction in Maize (Zea mays L) in Response to Soil Drying

et al. 2020

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The relationship between leaf water potential, soil water potential, and transpiration depends on soil and plant hydraulics and stomata regulation. Recent concepts of stomatal response to soil drying relate stomatal regulation to plant hydraulics, neglecting the loss of soil hydraulic conductance around the roots. Our objective was to measure the effect of soil drying on the soil-plant hydraulic conductance of maize and to test whether stomatal regulation avoids a loss of soil-plant hydraulic conductance in drying soils. We combined a root pressure chamber, in which the soil-root system is pressurized to maintain the leaf xylem at atmospheric pressure, with sap flow sensors to measure transpiration rate. The method provides accurate and high temporal resolution measurements of the relationship between transpiration rate and xylem leaf water potential. A simple soil-plant hydraulic model describing the flow of water across the soil, root, and xylem was used to simulate the relationship between leaf water potential and transpiration rate. The experiments were carried out with 5-week-old maize grown in cylinders of 9 cm diameter and 30 cm height filled with silty soil. The measurements were performed at four different soil water contents (WC). The results showed that the relationship between transpiration and leaf water potential was linear in wet soils, but as the soil dried, the xylem tension increased, and nonlinearities were observed at high transpiration rates. Nonlinearity in the relationship between transpiration and leaf water potential indicated a decrease in the soil-plant hydraulic conductance, which was explained by the loss of hydraulic conductivity around the roots. The hydraulic model well reproduced the observed leaf water potential. Parallel experiments performed with plants not being pressurized showed that plants closed stomata when the soil-plant hydraulic conductance decreased, maintaining the linearity between leaf water potential and transpiration rate. We conclude that stomata closure during soil drying is caused by the loss of soil hydraulic conductivity in a predictable way.

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Section: Introductionmentioning

confidence: 99%

Transpiration Reduction in Maize (Zea mays L) in Response to Soil Drying

et al. 2020

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“…Symbiosis between roots and mycorrhizal fungi, for example, positively affect water balance, energy balance, nutrient/element cycling and soil hydrophobicity 9,10 . Likewise, root hairs have been linked to phosphate uptake, rhizosphere soil structure formation 11 , root penetration 12 , water uptake 13 and rhizosheath (i.e. the weight of soil adhering strongly to roots upon excavation) formation in crop plants 14 .…”

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Micro-scale interactions between Arabidopsis root hairs and soil particles influence soil erosion

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Soil is essential for sustaining life on land. Plant roots play a crucial role in stabilising soil and minimising erosion, although these mechanisms are still not completely understood. Consequently, identifying and breeding for plant traits to enhance erosion resistance is challenging. Root hair mutants in Arabidopsis thaliana were studied using three different quantitative methods to isolate their effect on root-soil cohesion. We present compelling evidence that micro-scale interactions of root hairs with surrounding soil increase soil cohesion and reduce erosion. Arabidopsis seedlings with root hairs were more difficult to detach from soil, compost and sterile gel media than those with hairless roots, and it was 10-times harder to erode soil from roots with than without hairs. We also developed a model that can consistently predict the impact root hairs make to soil erosion resistance. Our study thus provides new insight into the mechanisms by which roots maintain soil stability.

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“…Spatial variability in root-soil contact (partial contact) may further add to this complexity (Carminati et al, 2013;de Willigen et al, 2018;Herkelrath et al, 1977;North & Nobel, 1997;Veen et al, 1992). Some of these features (mucilage, partial contact) have already been used in attempts to explain the hysteresis in the relation between xylem pressure and rates of root water uptake (Carminati et al, 2017). Yet it has not been thoroughly studied whether a more general understanding of how these features contribute to local heterogeneities in water flow and the delay in the redistribution of pressure can provide new insights into the puzzling hysteresis.…”

Section: Discussionmentioning

confidence: 99%

Spatial Heterogeneity Enables Higher Root Water Uptake in Dry Soil but Protracts Water Stress After Transpiration Decline: A Numerical Study

Jeetze

Zarebanadkouki

Carminati

2020

Water Resources Research

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A common assumption in models of water flow from soil to root is that the soil can be described in terms of its representative or effective behavior. Microscale heterogeneity and structure are thereby replaced by effective descriptions, and their role in flow processes at the root-soil interface is neglected. Here the aim was to explore whether a detailed characterization of the microscale heterogeneity at the scale of a single root impacts the relation between flow rate and pressure gradient. Numerical simulations of water flow toward a root surface were carried out in a two-dimensional domain with a randomized configuration of spatially variable unsaturated hydraulic conductivities and varying boundary conditions, that is, increasing and decreasing root water uptake rates. By employing Matheron's method, the soil hydraulic properties were varied, while the effective hydraulic conductivity (corresponding to the geometric mean) remained unchanged. Results show that domains with a uniform conductivity could not capture important features of water flow and pressure distribution in spatially variable domains. Specifically, increasing heterogeneity at the root-soil interface allowed to sustain higher root water uptake rates but caused a slower recovery in xylem suction after transpiration ceased. The significance of this is that, under critical conditions, when pressure gradients and flow rates are high, microscale heterogeneity may become an important determinant and should not be neglected in adequate descriptions of water flow from soil to root in dry soil.

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Root hairs enable high transpiration rates in drying soils

Cited by 128 publications

References 47 publications

Transpiration Reduction in Maize (Zea mays L) in Response to Soil Drying

Transpiration Reduction in Maize (Zea mays L) in Response to Soil Drying

Micro-scale interactions between Arabidopsis root hairs and soil particles influence soil erosion

Spatial Heterogeneity Enables Higher Root Water Uptake in Dry Soil but Protracts Water Stress After Transpiration Decline: A Numerical Study

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