Studies in the Water Relations of the Cotton Plant

Weatherley, P. E.

doi:10.1111/j.1469-8137.1951.tb05168.x

Cited by 95 publications

(23 citation statements)

References 13 publications

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“…As water becomes limiting, the magnitude of the daily fluctuation increases and eventually the soil and plant water potentials decrease. When soil water potential falls below some critical level, a combination of both soil and atmospheric conditions controls the plant water status (6,8,18,23,32 (19,20 Although our data suggest that the effective soil water potential in the root zone was about -10 bars, plant water potential data provide no information concerning the soil water potential profile. The distribution of soil matric potential with depth is shown in Figure 3.…”

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Influence of Soil Water Stress on Evaporation, Root Absorption, and Internal Water Status of Cotton

1971

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Diurnal variations in leaf water potential, diffusion resist.ance, relative water content, stem diameter, leaf temperature, and energy balance components were measured in cotton (Gossypium hirsutum L. var. Lankart 57) during drought stress under field conditions. A plot of leaf water potential against either relative water content or stem diameter during the 24-hour period yielded a closed hysteresis loop. The relation between ceil hydration and evaporation is discussed.Despite low soil water potential in the main root zone, significant plant evaporation rates were maintained. Root absorption rates as a function of soil depth were calculated from water content profiles measured with a neutron probe.The maximal root absorption rate of 3.5 X 10-' day-' occurred at the 75-centimeter depth, welil below the main root zone.Stomatal resistance of individual leaves during the daylight hours remained nearly constant at 2.5 seconds centimetereven though leaf water potentials approached -30 bars. A growth chamber study indicated stomatal closure occurred at potentials near -16 bars. Possible implications of high soil water stress in relation to stomatal funetion and growth are discussed. Based on an energy balance method, the actual to potential plant evapotranspiration ratio was 0.43 for the 24-hour period, indicating partial stomatal closure. A surface resistance, r,, of 4.0 seconds centimeter-' was calculated for the incomplete canopy with the use of the energy balance data. Alternatively, a canopy resistance of 1.3 seconds centimeter-' was attained from a relationship between leaf area and stomatal resistance of individual leaves. If the soil resistance was assumed to be very large and the canopy resistance was weighted for the fractional ground cover of the crop, the calculated surface resistance was 4.3 seconds centimeter-. Under these conditions, the two independent estimates of r, were in essential agreement.Significant enhancement of our understanding of the response of internal plant water status to changes in the evaporative demand, in the water potential in the root environment, and in illumination have been made by theoretical analysis and by experiments under controlled conditions, but parallel studies with plants growing in a natural environment are relatively rare. Because of a prolonged drought in central Texas, the 1969 summer growing season provided an opportunity for field study of the water status of cotton under high soil water stress. Accordingly, diurnal variations in plant and soil water status and evaporation rate during drought stress were measured for purposes of comparison with theoretical predictions and with results from experiments under controlled conditions.Field studies by Weatherley (32) and Slatyer (23) have shown that plant water status is directly influenced by evaporative demand until a critical soil water potential is reached. The transpiration rates presented in these studies were inferred from a technique with the use of excised leaves and cannot be interpreted in absolute...

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Influence of Soil Water Stress on Evaporation, Root Absorption, and Internal Water Status of Cotton

1971

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“…In a study of the water relations of the commercial cotton crop in East Africa (Weatherley, 1951), it was found that above a certain critical level of soil water tension, the diurnal pattern of changes in relative turgidity (R.T.) of the cotton leaves showed a partial recovery from daytime low values during the period up to, and around, midnight. There was little further rise in R.T. after this, in spite of the transpiration being virtually zero.…”

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confidence: 99%

Controlled Environment Studies of the Nature and Origins of Water Deficits in Plants

Macklon

Weatherley

1965

New Phytologist

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SUMMARYDepression of water potential. All '(d.p.d.), in the leaves, transpiration and stomatal aperture were measured on Ricinus cornmunis plants subjected to controlled levels of atmospheric evaporation m a climatological wind tunnel.It was found that the leaf All' of transpiring plants rooted in water took up a value of about 5 atm and remained unaffected by large changes in transpirational flux. When water was replaced by an osmoticum round the roots, leaf tJV merely rose to approach the AW'' of the medium. These results indicate that root resistance plays little part in determining levels of leaf ATI'above i; atm.

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“…That this can be of considerable ecological significance has been demonstrated for field grown cotton (Weatherley, 1951) where it was suggested that leaf water deficits which persisted throughout the night were reflections of the state of the water in the soil adjacent to the root surface (perirhizal zones). This hypothesis can be represented in terms of water potential by the following equation:…”

Section: Introductionmentioning

confidence: 99%

The Effect of Transpiration Rate on the Leaf Water Potential of Sand and Soil Rooted Plants

Tinklin

Weatherley

1968

New Phytologist

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SUMMARYTwelve-week-old Ricimis comiminis plants were transplanted to boxes of sand or soil in which the water table was maintained at various levels below the root system. The boxes were placed in a climatological wind tunnel and transpiration varied by altering the humidity of the air stream. Responses in the water potential depression (= suction force or D.P.D.) of the leaves (AH^i) and stomatal conductance were followed.With a fine sand it was found that when the water table was high (15 cm below the roots) AIF, was 6 atm. irrespective of the rate of transpiration and behaved therefore as if the roots were surrounded by f^ree water as previously shown. \\'hen the water table was 25 cm below the roots, A IF, was also 6 atm. provided the transpiration rate was low (0.4 g/dm^ leaf/hour) but when the transpiration rate was raised threefold, Afr, rose steeply to a value of 12 atm., a steady state value being approached in about 8 hours (see Fig. 3). On reducing the transpiration rate, A IF, returned to 6 atm. This rise in A IF, is interpreted as due to a rise in the AfF of the water in the sand at the root surface, this in turn resulting from the low water conductivity of the sand at this height above the water table. Varying the humidity continuously between saturation and about ^0°/^ relative humidity through a 24-hour cycle produced a regular 24-hour cycle of transpiration (see Figs. 4, 5 and 6). Responses in A IF, in plants rooted in fine sand, clay soil and moorland soil were explicable in terms of the above hypothesis of the development of perirhizal zones of soil water tension.These results suggest that much of the ecologically significant water stress in plants is a manifestation of the dynamic gradients of water potential developing in the perirhizal zones and that these can be considerable even when the water stress in the bulk of the soil is virtually zero.

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Studies in the Water Relations of the Cotton Plant

Cited by 95 publications

References 13 publications

Influence of Soil Water Stress on Evaporation, Root Absorption, and Internal Water Status of Cotton

Influence of Soil Water Stress on Evaporation, Root Absorption, and Internal Water Status of Cotton

Controlled Environment Studies of the Nature and Origins of Water Deficits in Plants

The Effect of Transpiration Rate on the Leaf Water Potential of Sand and Soil Rooted Plants

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