Leaf water potentials of pasture plants in a semi-arid subtropical environment

1975 ◽  
Vol 15 (76) ◽  
pp. 645 ◽  
Author(s):  
DCI Peake ◽  
GD Stirk ◽  
EF Henzell
Keyword(s):  
Water Stress ◽  
Leaf Water ◽  
Panicum Maximum ◽  
Research Station ◽  
Buffel Grass ◽  
Heteropogon Contortus ◽  
Drought Avoidance ◽  
Water Potentials ◽  
Severe Water Stress ◽  
Pasture Plants

Leaf water potentials (�1) were measured on pasture plants at the Narayen Research Station in southern Queensland. The main findings were: 1. There were marked differences between species in the value of �1, measured during drought. Lucerne (Medicago sativa cv. Hunter River) and buffel grass (Cenchrus ciliaris cv. Biloela) usually showed a lower (i.e. more negative) �1 than Siratro (Macroptilium atropurpureum cv. Siratro), when they were grown together in a mixed pasture. Siratro seemed to possess a useful degree of drought avoidance. High drought resistance was observed in buffel grass; this was attributed to its tolerance of water stress. Green panic (Panicum maximum var. trichoglume cv. Petrie) was found to have as low a �1 as lucerne during drought when the two species were grown with Siratro in a mixed pasture. 2. The plants were under severe water stress before all the available water was removed from the deeper soil horizons. 3. �1 was lower in nitrogen-fertilized buffel grass or spear grass (Heteropogon contortus), than in the corresponding unfertilized controls. 4. The vapour-exchange and dye-marker densiometric methods gave different values for �1 in buffel grass, green panic and Siratro; the vapour exchange technique recorded lower, i.e, more negative figures than the other method when the plants were under severe water stress. The two methods gave similar values for lucerne. The relation between the values obtained for buffel grass by the two methods was affected by nitrogen fertilization. The reaction of sown pasture plants to drought at Narayen is discussed.

Adaptation to Water Stress of the Leaf Water Relations of Four Tropical Forage Species

1980 ◽  
Vol 7 (2) ◽  
pp. 207 ◽  
Author(s):  
JR Wilson ◽  
MM Ludlow ◽  
MJ Fisher ◽  
E Schulze
Keyword(s):  
Water Stress ◽  
Water Content ◽  
Water Relations ◽  
Bound Water ◽  
Leaf Tissue ◽  
Dry Weight ◽  
Panicum Maximum ◽  
Soil Drying ◽  
Buffel Grass ◽  
Heteropogon Contortus

Three tropical grasses, green panic (Panicum maximum var, trichoglume), spear grass (Heteropogon contortus) and buffel grass (Cenchrus ciliaris) and the tropical legume siratro (Macroptilium atropurpureum), were grown in plots in a semi-arid field environment. The water relations characteristics of leaves from plants subjected to a soil drying cycle were compared with those of unstressed leaves from plants in irrigated plots. Minimum water potentials attained in the stressed leaves were c. -44, - 38, - 33 and - 13 bar for the four species, respectively. The grass leaves adjusted osmotically to water stress, apparently through accumulation of solutes, so that there was a decrease in osmotic potential at full turgor (Ψπ100) of 5.5, 3.9 and 7.1 bar, and in water potential at zero turgor (Ψ0) of 8.6, 6.5 and 8.6 bar for green panic, spear grass and buffel respectively. Water stress appeared to increase slightly the proportion of bound water (B) and the bulk modulus of elasticity (ε) of the grass leaves, but it did not alter the relative water content at zero turgor (RWC0) or the ratio of turgid water content to dry weight of the tissue. The Ψπ100 and Ψ0 of stressed siratro leaves decreased by 2.5-4 bar and 3-5 bar respectively when subjected to soil drying cycles. These changes could be explained by the marked decrease in the ratio of turgid water content to dry weight of the leaf tissue rather than by accumulation of solutes. The values of RWC0 and ε for siratro leaves were not altered by stress but, in contrast to the grasses, B was apparently decreased although the data exhibited high variability. Adjustments in Ψπ100 and Ψ0 of stressed leaves of buffel grass and siratro were largely lost within 10 days of rewatering.

Changes in Levels of Solutes During Osmotic Adjustment to Water Stress in Leaves of Four Tropical Pasture Species

1981 ◽  
Vol 8 (1) ◽  
pp. 77 ◽  
Author(s):  
CW Ford ◽  
JR Wilson
Keyword(s):  
Water Stress ◽  
Organic Acids ◽  
Osmotic Adjustment ◽  
Inorganic Ions ◽  
Arid Environment ◽  
Low Molecular Weight ◽  
Panicum Maximum ◽  
Buffel Grass ◽  
Heteropogon Contortus ◽  
Macroptilium Atropurpureum

Three tropical grasses, green panic (Panicum maximum var. trichoglume), buffel grass (Cenchrus ciliaris), and spear grass (Heteropogon contortus), and a tropical legume, siratro (Macroptilium atropurpureum), were field-grown in a semi-arid environment. One set of plants was well watered, while another set was subjected to a continuous 35-day drying cycle. Samples of specific leaves were taken at the beginning, middle and end of the drying cycle, and 1, 5 and 14 days after rewatering. The major low-molecular-weight solutes which accumulated in the grasses during water stress were the inorganic ions sodium (green panic), potassium (buffel and spear grass) and chloride (all grasses). Accumulation of these ions largely accounted for the osmotic adjustments determined from a previous study of water relations of the leaves. Concentrations of the minor constituents glucose and fructose increased only slightly in the stressed grasses, whereas levels of sucrose, the major carbohydrate component, increased substantially, particularly in spear grass. Inositol accumulated to a small extent in spear grass. Differences between the grasses were evident in the organic acid spectrum and also in changes in concentration of organic acids due to water stress. In water-stressed tissue, malate levels increased in green panic and spear grass but were reasonably constant in buffel grass. Aconitate concentrations (not detected in buffel grass) decreased in stressed green panic, but increased in spear grass. Oxalate (only trace quantities in spear grass) was a major component in green panic and buffel grass, but did not appear to vary with increase in water stress. Succinate accumulated only in stressed spear grass. The contribution of carbohydrates and organic acids to the osmotic adjustment was relatively small. Proline accumulated to varying degrees in all stressed grasses. Betaine occurred only in trace amounts in spear grass, but accumulated substantially in green panic and buffel grass. Water-stressed leaves of siratro did not accumulate inorganic ions, sugars, organic acids, proline or betaine, but pinitol levels increased. Implications of the results relating osmotic adjustment to changes in chemical composition are discussed.

Water stress affects the productivity, growth components, competitiveness and water relations of phalaris and white clover growing in a mixed pasture

1992 ◽  
Vol 43 (3) ◽  
pp. 659 ◽  
Author(s):  
L Guobin ◽  
DR Kemp ◽  
GB Liu
Keyword(s):  
Water Stress ◽  
Soil Water ◽  
White Clover ◽  
Leaf Growth ◽  
Leaf Water ◽  
Water Potentials ◽  
Relative Water ◽  
Dry Conditions ◽  
Leaf Appearance ◽  
Water Contents

The effect of water stress during summer and recovery after rain on herbage accumulation, leaf growth components, stomatal conductance and leaf water relations of white clover (Trifolium repens cv. Haifa) and phalaris (Phalaris aquatica cv. Australian Commercial) was studied in an established mixed pasture under dryland (dry) or irrigated (wet) conditions. Soil water deficits under dry conditions reached 150 mm and soil water potentials in the top 20 cm declined to nearly -2 MPa after 50 days of dry weather. Water stress severely restricted growth of both species but then after rain fell, white clover growth rates exceeded those of phalaris. Under irrigation, white clover produced twice the herbage mass of phalaris but under dry conditions herbage production was similar from both species. Leaf appearance rates per tiller or stolon were slightly higher for white clover than phalaris but were reduced by 20% under water stress in both species. Leaf or petiole extension rates were more sensitive to water stress than leaf appearance rates and declined by 75% in phalaris and 90% in white clover. The ratio of leaf or petiole extension rates on dry/wet treatments was similar for both species in relation to leaf relative water contents, but in relation to leaf water potentials phalaris maintained higher leaf growth rates. Phalaris maintained a higher leaf relative water content in relation to leaf water potentials than did white clover and also maintained higher leaf water potentials in relation to the soil water potential in the top 20 cm. Stomata1 conductances for both species declined by 80-90% with increasing water stress, and both species showed similar stomatal responses to bulk leaf water potentials and leaf relative water contents. It is suggested that the poorer performance of white clover under water stress may be due principally to a shallower root system than phalaris and not due to any underlying major physiological differences. The white clover cultivar used in this study came from the mediterranean region and showed some different responses to water stress than previously published evidence on white clover. This suggests genetic variation in responses to water stress may exist within white clover. To maintain white clover in a pasture under dry conditions it is suggested that grazing practices aim to retain a high proportion of growing points.

Effect of Water Stress on Stomatal Conductance and Leaf Water Relations of Leaves Along Current-Year Branches of Peach

1989 ◽  
Vol 16 (6) ◽  
pp. 549 ◽  
Author(s):  
SL Steinberg ◽  
MJ Mcfarland ◽  
JC Miller
Keyword(s):  
Water Stress ◽  
Stomatal Conductance ◽  
Water Potential ◽  
Water Status ◽  
Stomatal Closure ◽  
Water Flux ◽  
Leaf Water ◽  
Leaf Water Status ◽  
Mature Leaves ◽  
Water Potentials

A gradation, that reflects the maturity of the leaves, exists in the leaf water, osmotic and turgor potential and stomatal conductance of leaves along current and 1-year-old branches of peach. Predawn leaf water potentials of immature folded leaves were approximately 0.24 MPa lower than mature leaves under both well-watered and dry conditions. During the daytime the leaf water potential of immature leaves reflected the water potential produced by water flux for transpiration. In well- watered trees, mature and immature unfolded leaves had a solute potential at least 0.5 MPa lower than immature folded leaves, resulting in a turgor potential that was approximately 0.8 MPa higher. The turgor requirement for growth appeared to be much less than that maintained in mature leaves. As water stress developed and leaf water potentials decreased, the osmotic potential of immature folded leaves declined to the level found in mature leaves, thus maintaining turgor. In contrast, mature leaves showed little evidence of turgor maintenance. Stomatal conductance was lower in immature leaves than in fully mature leaves. With the onset of water stress, conductance of mature leaves declined to a level near that of immature leaves. Loss of turgor in mature leaves may be a major factor in early stomatal closure. It was concluded that osmotic adjustment played a role in maintenance of a leaf water status favorable for some growth in water-stressed immature peach leaves.

Water Relations of Root-Pruned Jarrah (Eucalyptus marginata Donn ex Smith) Saplings

1987 ◽  
Vol 35 (6) ◽  
pp. 653 ◽  
Author(s):  
DS Crombie ◽  
JT Tippett ◽  
DJ Gorddard
Keyword(s):  
Water Relations ◽  
Phytophthora Cinnamomi ◽  
Leaf Water ◽  
Lateritic Soil ◽  
Root Pruning ◽  
Deep Roots ◽  
Eucalyptus Marginata ◽  
Water Potentials ◽  
Severe Water Stress ◽  
Leaf Shedding

Roots were pruned from jarrah (Eucalyptus marginata Donn ex Smith) saplings to simulate the effects of root loss induced by Phytophthora cinnamomi Rands. Stomatal conductance was more sensitive to root loss than was leaf water potential. Stomatal conductances of trees on moist soils declined when more than 50% of roots were removed but were more variable and were affected more severely by root pruning when soils were dry. Predawn leaf water potentials were unaffected by removal of up to 80% of roots irrespective of whether surface soils were dry or moist. The effects of root pruning on midday water potentials were variable especially when soils were dry. Leaf shedding and efficient stornatal closure prevented severe water stress developing in leaves until nearly 90% of the roots had been removed. It is suggested that destruction of the deep 'sinker' roots by P. cinnamomi has greater effects on jarrah's water relations during summer than does loss of shallow roots. The deep roots are especially important as jarrah grows on highly developed lateritic soil profiles.

scholarly journals Comparison of Strawberry F. chilocnsis and F. ×ananassa in Response to Water Stress: I. Leaf Water Potential, Relative Water Content, and Gas Exchange Characteristics

HortScience ◽  
1996 ◽  
Vol 31 (4) ◽  
pp. 601c-601
Author(s):  
Chuhe Chen ◽  
J. Scott Cameron ◽  
Stephen F. Klauer
Keyword(s):  
Water Stress ◽  
Gas Exchange ◽  
Water Potential ◽  
Water Content ◽  
Leaf Water Potential ◽  
Relative Water Content ◽  
Leaf Water ◽  
Severe Water Stress ◽  
Relative Water ◽  
Gas Exchange Characteristics

Leaf water potential (LWP), relative water content (RWC), gas exchange characteristics, and specific leaf weight (SLW) were measured six hours before, during, and after water stress treatment in F. chiloensis and F. ×ananassa grown in growth chambers. The leaves of both species showed significantly lower LWP and RWC as water stress developed. F. ×ananassa had consistency lower LWP under stressed and nonstressed conditions than F. chiloensis. F. ×ananassa had higher RWC under nonstressed conditions, and its RWC decreased more rapidly under water stress than F. chiloensis. In comparison to F. ×ananassa, F. chiloensis had significantly higher CO2 assimilation rate (A), leaf conductance (LC), and SLW, but not transpiration rate (Tr), under stressed and nonstressed conditions. LC was the most sensitive gas exchange characteristic to water stress and decreased first. Later, A and stomatal conductance were reduced under more severe water stress. A very high level of Tr was detected in F. ×ananassa under the most severe water stress and did not regain after stress recovery, suggesting a permanent damage to leaf. The Tr of F. chiloensis was affected less by water stress. Severe water stress resulted in higher SLW of both species.

Stem and leaf water potentials, gas exchange, sap flow, and trunk diameter fluctuations for detecting water stress in lemon trees

Trees ◽  
2005 ◽  
Vol 20 (1) ◽  
pp. 1-8 ◽  
Author(s):  
M. Fernanda Ortuño ◽  
Yelitza García-Orellana ◽  
Wenceslao Conejero ◽  
M. Carmen Ruiz-Sánchez ◽  
Juan José Alarcón ◽  
...  
Keyword(s):  
Water Stress ◽  
Gas Exchange ◽  
Sap Flow ◽  
Leaf Water ◽  
Trunk Diameter ◽  
Water Potentials ◽  
Trunk Diameter Fluctuations

Effects of preconditioning on subsequent water relations, stomatal sensitivity, and photosynthesis in osmotically stressed black spruce

1989 ◽  
Vol 67 (8) ◽  
pp. 2240-2244 ◽  
Author(s):  
Janusz J. Zwiazek ◽  
Terence J. Blake
Keyword(s):  
Water Stress ◽  
Water Relations ◽  
Black Spruce ◽  
Water Potentials ◽  
Conditioning Treatment ◽  
Severe Water Stress ◽  
Use Efficiency ◽  
Stomatal Sensitivity ◽  
Stress Conditioning ◽  
Osmotic Potentials

The effects of stress conditioning with polyethylene glycol on water relations and photosynthesis in preconditioned ramets were compared with those of unconditioned black spruce (Picea mariana Mill. BSP). Preconditioned plants maintained lower osmotic and water potentials and higher turgor potentials (measured as a difference between osmotic and water potentials), but photosynthetic rates were similar in both groups of plants. The conditioning treatment increased stomatal sensitivity to water stress, and stomatal conductance was lower in preconditioned plants soon after water stress was imposed. Preconditioned plants maintained significantly lower osmotic potentials during a severe water stress and were able to maintain turgor at the time when unconditioned plants wilted. Water-use efficiency was not affected by stress-conditioning treatment.

Nitrogen response of pasture grasses on duplex soils formed from granite in southern Queensland

1975 ◽  
Vol 15 (75) ◽  
pp. 498 ◽  
Author(s):  
EF Henzell ◽  
DCI Peake ◽  
Mannetje L 't ◽  
GB Stirk
Keyword(s):  
High Probability ◽  
Growing Season ◽  
Research Station ◽  
Lower Yield ◽  
Nitrogen Response ◽  
Buffel Grass ◽  
Heteropogon Contortus ◽  
Pasture Grasses ◽  
Native Pasture ◽  
Drought Damage

The response to fertilizer N of native pasture containing black spear grass (Heteropogon contortus) and of buffel grass (Cenchrus ciliaris cv. Biloela) was measured on granitic soils at the Narayen Research Station, in southern Queensland. Experiments were carried out in grazed and ungrazed areas. In 1968-69, which was as dry as any year on record for this district, neither pasture responded to N; in wetter years both did, the native pasture giving a lower yield than the sown buffel grass pasture. Grazed areas that received 168 kg N ha-1 year-1 as urea did not respond to further additions. Analysis of buffel grass yields over intervals of 8 to 16 weeks during the growing season indicated that 1. there was no growth or response to N unless the rainfall exceeded about 30 mm, 2. above 30 mm the response to near-optimum rates of N increased with rainfall, 3. buffel grass grown with such rates of N produced more than four times as much DM per unit rainfall as buffel grass without added N when 100 mm of rain fell. Examination of rainfall records suggested that there is a high probability of worthwhile responses to N on these soils at Narayen.Spear grass and other native grass plants were killed by high rates of N during the first, dry season. The results of a pot trial with Biloela buffel grass and a late flowering strain of spear grass showed that N increased drought damage in both grasses but spear grass was more susceptible than buffel grass.

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