On the Relationship Between Transpiration Rate and Leaf Water Potential

Abstract

SUMMARYThe aim was to vary the transpiration rate of water culture plants and to measure corresponding values of ISW, the leaf water potential depression ( = DPD = suction force), as well as relative water content (relative turgidity) and stomatal aperture. On the Ohm-law analogy tS.W and transpiration rate should be linearly related.Ricinus communis plants were placed in a wind tunnel and the transpiration rate was varied by changing the level of the relative humidity of the air stream. With increasing rate of transpiration, A [r rose steeply to a value of about 6 atmospheres at which it remained virtually constant (Fig. i). Thus from very low transpiration rates to the highest obtainable, far from AIF rising linearly with transpiration, there was no response in AW and similarly no response in relative water content and stomatal resistance. When transpiration was reduced to zero the leaves still maintained a ATFof about 3 atmospheres instead of zero, but reasons are put for\vard for considering this value to present water saturation.The main resistance to water movennent in the plant was shown to reside in the roots. If a leaf was detached from a transpiring plant and allowed to continue transpiration at a similar rate, water being freely supplied to the cut end of the petiole, its A IF fell from 6 to 3.5 atmospheres (Fig. 3). Thus the resistance must lie 'below' the petiole. Similarly it was shown to lie below the stem.The constancy of leaf APF in the face of large changes in flux of water through the roots, implies that the root resistance declines in step with the rise in flux. A simple hydraulic model is presented which would behave in this way.

A Negative Hydraulic Message from Oxygen-Deficient Roots of Tomato Plants? (Influence of Soil Flooding on Leaf Water Potential, Leaf Expansion, and Synchrony between Stomatal Conductance and Root Hydraulic Conductivity)

“…How the synchrony between stomatal aperture and L, is achieved is not known. The possibility that L, increases as water flux increases in response to stomatal opening (the rotameter flow gauge analogy of Tinklin and Weatherley, 1966) seems unlikely, since we found a linear rather than an upwardly curving relationship between driving force and the resultant Jv that the Tinklin and Weatherley analogy would predict (Fig. 3A).…”

Efficiency and Regulation of Water Transport in Some Woody and Herbaceous Species

“…degree at the University of California, Riverside. by measuring the response of 4 have not (17), and Barrs (1) observed both types of response with different species. These differences may be due to differences in methodology; but it is also possible that important differences exist between species in their ability to transport water.…”

In Situ Measurements of Leaf Water Potential and Resistance to Water Flow in Corn, Soybean, and Sunflower at Several Transpiration Rates

“…and Stoker and Weatherly (1971) with cotton (Gossypium hirsutum L.) and sunflower (Helianthus annus L.) found water potential gradients to remain constant over a wide range of transpiration rates. Tinklin and Weatherly (1966) noted that most of the nonlinearity and indeed most of the resistance in castor bean appeared to be associated with the root system. All the above workers were puzzled by their observation of a 3-8-bar potential gradient at zero transpiration.…”