The response of pressure volume curve water parameters and root system hydraulic architecture of two apple rootstocks to drought stress

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, Krs, 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.

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Elastic constants of inflated lobes of dog lungs

Journal of Applied Physiology ◽

10.1152/jappl.1976.40.4.508 ◽

1976 ◽

Vol 40 (4) ◽

pp. 508-513 ◽

Cited By ~ 89

Author(s):

S. J. Lai-Fook ◽

T. A. Wilson ◽

R. E. Hyatt ◽

J. R. Rodarte

Keyword(s):

Bulk Modulus ◽

Young’S Modulus ◽

Elastic Constants ◽

Young's Modulus ◽

Poisson Ratio ◽

Inflation Pressure ◽

Initial State ◽

Volume Curve ◽

Pressure Volume Curve ◽

Indentation Tests

The elastic constants of dog lungs were determined at various degrees of inflation. In one set of experiments, the lobes were subjected to deformations that approximated the conditions of uniaxial loading. These data, together with the bulk modulus data obtained from the local slope of the pressure-volume curve, were used to determine the two elastic moduli that are needed to describe small nonuniform deformations about an initial state of uniform inflation. The bulk modulus was approximately 4 times the inflation pressure, and Young's modulus was approximately 1.5 times the inflation pressure. In a second set of experiments, lobes were subjected to indentation tests using cylindric punches 1–3 cm in diameter. The value for Young's modulus obtained from these data was slightly higher, approximately twice the inflation pressure. These experiments indicate that the lung is much more easily deformable in shear than in dilatation and that the Poisson ratio for the lung is high, approximately 0.43.

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Lung volumes and alveolar expansion pattern in immature rabbits treated with serum-diluted surfactant

Journal of Applied Physiology ◽

10.1152/japplphysiol.01043.2003 ◽

2004 ◽

Vol 97 (4) ◽

pp. 1408-1413 ◽

Cited By ~ 4

Author(s):

Yongmei Xu ◽

Tsutomu Kobayashi ◽

Xiaoguang Cui ◽

Keisuke Ohta ◽

Chiharu Kabata ◽

...

Keyword(s):

Mechanical Ventilation ◽

Acute Respiratory Distress Syndrome ◽

Respiratory Distress Syndrome ◽

Respiratory Distress ◽

Distress Syndrome ◽

Ringer Solution ◽

Natural Surfactant ◽

Volume Curve ◽

Pressure Volume Curve ◽

Expansion Pattern

In acute respiratory distress syndrome, mechanical ventilation often induces alveolar overdistension aggravating the primary insult. To examine the mechanism of overdistension, surfactant-deficient immature rabbits were anesthetized with pentobarbital sodium, and their lungs were treated with serum-diluted modified natural surfactant (porcine lung extract; 2 mg/ml, 10 ml/kg). By mechanical ventilation with a peak inspiration pressure of 22.5 cmH2O, the animals had a tidal volume of 14.7 ml/kg (mean), when 2.5 cmH2O positive end-expiratory pressure was added. This volume was similar to that in animals treated with nondiluted modified natural surfactant (24 mg/ml in Ringer solution, 10 ml/kg). However, the lungs fixed at 10 cmH2O on the deflation limbs of the pressure-volume curve had the largest alveolar/alveolar duct profiles (≥48,000 μm2), accounting for 38% of the terminal air spaces, and the smallest (<6,000 μm2), accounting for 31%. These values were higher than those in animals treated with nondiluted modified natural surfactant ( P < 0.05). We conclude that administration of serum-diluted surfactant to immature neonatal lungs leads to patchy overdistension of terminal air spaces, similar to the expansion pattern that may be seen after dilution of endogenous surfactant with proteinaceous edema fluid in acute respiratory distress syndrome.

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Improved measurements of shear modulus and pleural membrane tension of the lung

Journal of Applied Physiology ◽

10.1152/jappl.1979.47.1.175 ◽

1979 ◽

Vol 47 (1) ◽

pp. 175-181 ◽

Cited By ~ 65

Author(s):

M. A. Hajji ◽

T. A. Wilson ◽

S. J. Lai-Fook

Keyword(s):

Shear Modulus ◽

Transpulmonary Pressure ◽

Elastic Half Space ◽

Concentrated Force ◽

Membrane Area ◽

Volume Curve ◽

Pressure Volume Curve ◽

Pressure Independent ◽

Work Done ◽

The Continuum

The continuum solution for the deformation of an elastic half space covered by a membrane is used to interpret measurements of the indentation of lung lobes under a column of fluid. The shear modulus mu of the underlying parenchyma is found to be approximately 0.7 times transpulmonary pressure, independent of species size. The tension in the pleural membrane T increases rapidly with increasing membrane area. For dog lungs, the value of T is 10(3) to 10(4) dyn/cm. For the larger species tested, pigs and horses, T is larger. The continuum solution shows that a concentrated force applied to the pleural surface is distributed over a distance T/mu as it is transmitted across the pleural membrane. The membrane is important in determining the displacement produced by forces that act within a region that is small compared to this distance, approximately 2 cm for dog lungs. By comparing the tension-area curve of the pleural membrane with the pressure-volume curve of the lobe, it is found that the pleural membrane contributes about 20% of the work done by the lung during deflation.

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