Water-Sensitive Periods during the Reproductive Growth Phase of Glycine max L. I. Regression Model for estimating daily leaf water potential

Peltier-cooled thermocouple dewpoint hygrometers were used to measure leaf water potentials at several transpiration rates on intact corn (Zea mays L.), soybean (Glycine max (L.) Merr.), and sunflower (Helianthus annus L.), grown in a controlled environment in silica sand rooting media frequently watered with nutrient solution. Hygrometers were left in position for the duration of measurements on each plant, but tests showed this to have little effect on measured potentials. Measured potentials were found to be linearly related to the transpiration rates (correlation coefficients greater than 0.98). Extrapolated values of leaf water potential at zero transpiration were within a few tenths bar of measured nutrient-solution potentials. These results indicated that plant resistances to water flow remained constant from near zero transpiration up to the maximum obtained average rates of 1.8–3.0 g dm−2 h−1. The magnitude of the resistance varied considerably from plant to plant even within a single cultivar of one species and definite conclusions as to interspecies differences in resistance were not made. Estimates of the relative resistance in the root, stalk, and the leaf that were made for a few plants were similar to previously published results.

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Soybean (Glycine max) – Velvetleaf (Abutilon theophrasti) Interspecific Competition

Weed Science ◽

10.1017/s0043174500060732 ◽

1987 ◽

Vol 35 (5) ◽

pp. 647-653 ◽

Cited By ~ 28

Author(s):

Philip H. Munger ◽

James M. Chandler ◽

J. Tom Cothren ◽

Frank M. Hons

Keyword(s):

Glycine Max ◽

Stomatal Conductance ◽

Water Potential ◽

Interspecific Competition ◽

Soil Water ◽

Leaf Water Potential ◽

Abutilon Theophrasti ◽

Leaf Water ◽

Water Extraction ◽

Soil Water Extraction

In a 2-yr field study conducted on a Weswood silt loam soil (Fluventic Ustochrepts), interspecific competition between soybeans [Glycine max(L.) Merr. ‘Hutton′] and velvetleaf (Abutilon theophrastiMedik. # ABUTH) resulted in greater than 40 and 50% reductions in soybean and velvetleaf seed yield, respectively. Leaf area index, number of mainstem nodes, total number of leaves, and plant dry weight of monocultured and intercropped velvetleaf differed significantly as early as 4 weeks after emergence. Interspecific competition had litttle or no effect on soybean morphology before 8 weeks after emergence. Soil water extraction occurred to 1-m depths in a monoculture of velvetleaf (five plants/m2) in 1984 and 1985. Monocultured soybeans (32.5 plants/m2) extracted water from a 1.5-m or greater depth of the soil profile during the same years. Soil water extraction in the intercropped plots resembled that of the monocultured velvetleaf treatment until soybeans attained R6, when soil water was extracted to a 1.5-m depth. The potential for interspecific competition for water existed early in the season before late-season soybean root development. Relative water content and leaf water potential (Ψw1) did not differ (0.05) between monocultured and intercropped soybeans in 1984 or 1985. In 1985, Ψw1differed between monocultured and intercropped velvetleaf during anthesis. Leaf water potential values in the youngest, fully expanded leaves were approximately 0.3 and 0.4 MPa lower during midmorning and midday hours, respectively, in intercropped and monocultured velvetleaf. Transpiration and stomatal conductance did not differ between monocultured and intercropped soybeans or velvetleaf at any time during 1984. Photosynthetic and transpiration rates, stomatal conductance, and Ψw1were lower in intercropped than in monocultured velvetleaf during anthesis in 1985, suggesting interspecific competition for soil water. Soybean water relations were not affected in either year. The data suggest that soybean yield reductions in soybean-velvetleaf interspecific competition are attributable to resource limitations other than water in south-central Texas.

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LEAF WATER CONTENT AND POTENTIAL IN CORN, SORGHUM, SOYBEAN, AND SUNFLOWER

Canadian Journal of Plant Science ◽

10.4141/cjps74-028 ◽

1974 ◽

Vol 54 (1) ◽

pp. 185-195 ◽

Cited By ~ 13

Author(s):

H. H. NEUMANN ◽

G. W. THURTELL ◽

K. R. STEVENSON ◽

C. L. BEADLE

Keyword(s):

Water Potential ◽

Water Content ◽

Leaf Water Potential ◽

Leaf Water ◽

Leaf Water Content ◽

Relative Water ◽

Helianthus Annus ◽

Glycine Max L ◽

Water Contents

The Peltier-cooled thermocouple dewpoint hygrometer technique of in situ measurement of leaf water potential was further developed. The observed response of the instrument agreed so well with theoretical analysis that calibration based on theory was within 1% of that obtained using salt solutions of known water potential. Simultaneous measurements with the hygrometer and a beta gauge were made to derive the leaf water content–potential relationships for several crop plants. Results showed relative water contents dropping only to near 0.95 for mature corn (Zea mays L.); sorghum (Sorghum vulgare Pers.); and sunflower (Helianthus annus L.) leaves, and to 0.90 for not quite mature soybean (Glycine max (L.) Merr.) leaves as potentials declined from near −1 bar to the plant wilting point (−8 to −14 bars). Further decline of leaf water potential resulted in relatively much greater loss of leaf water.

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Water deficits change dry matter partitioning and seed yield in narrow-leafed lupins (Lupinus angustifolius L.)

Australian Journal of Agricultural Research ◽

10.1071/ar9910471 ◽

1991 ◽

Vol 42 (3) ◽

pp. 471 ◽

Cited By ~ 34

Author(s):

RJ French ◽

NC Turner

Keyword(s):

Water Potential ◽

Water Deficit ◽

Leaf Water Potential ◽

Seed Yield ◽

Growth Rates ◽

Leaf Water ◽

Reproductive Growth ◽

Water Deficits ◽

First Order ◽

Severe Water Deficit

lrrigation treatments were imposed in the field on an indeterminate cultivar of narrow-leafed lupins (Lupinus angustifolius L., cv. Danja) and on a breeding line with reduced branching (75A/329) so that they experienced no water-deficits (frequently irrigated), a transient mild water-deficit or a transient severe water-deficit during early reproductive growth, or continuous severe water-deficit during reproductive growth (unirrigated). Both leaf water potential and leaf conductance declined in all treatments in which a water-deficit was imposed. Differences in leaf conductance were apparent before differences in leaf water potential: conductance declined to 40% and 30% of the frequently irrigated controls in the transient mild and severe water-deficit treatments, respectively. Leaf water potential declined to -1 - 1 MPa and -1.6 MPa, respectively, in the transient mild and severe water-deficit treatments, compared to between -0 - 65 and -0 - 95 MPa for the frequently irrigated controls. Seed yield and total dry weight were reduced in the transient severe water-deficit and unirrigated treatments, but were no different from the frequently irrigated treatment when the water-deficit was transient and mild. However both transient water-deficit treatments produced more main-stem seed yield than the frequently irrigated treatment, especially in the reduced-branching line 75A/329. The transient mild water-deficit treatment also produced more first-order apical axis yield than the frequently irrigated treatment. These yield increases were mainly due to a greater yield of seed per pod, although on the first-order apical axes there was also a tendency to set more pods. The greater seed yield per pod in the transient water-deficit treatments was due to an apparent redirection of assimilate from vegetative to reproductive growth. This was not due to a smaller reduction in reproductive growth rates than in vegetative growth rates, but to an acceleration of reproductive growth that was maintained after stress relief. The same early acceleration of reproductive growth was also observed in unirrigated treatments, but the severe stress which persisted throughout later reproductive growth reduced pod growth rates and negated the early advantage.

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