Leaf enlargement and metabolic rates in corn, soybean, and sunflower at various leaf water potentials.
TL;DR: Although leaf enlargement did not occur initially, enlargement resumed toward the end of the desiccation period, however, the rate of enlargement was not as rapid as in the well watered control, nor did it return to the control rate when the plant was rewatered.
Abstract: Rates of photosynthesis, dark respiration, and leaf enlargement were studied in soil-grown corn (Zea mays), soybean (Glycine max), and sunflower (Helianthus annuus) plants at various leaf water potentials. As leaf water potentials decreased, leaf enlargement was inhibited earlier and more severely than photosynthesis or respiration. Except for low rates of enlargement, inhibition of leaf enlargement was similar in all three species, and was large when leaf water potentials dropped to about -4 bars.Intact sunflower leaves were held for 4 days at leaf water potentials which permitted maximal photosynthesis and respiration, but which inhibited leaf enlargement. Although leaf enlargement did not occur initially, enlargement resumed toward the end of the desiccation period. However, the rate of enlargement was not as rapid as in the well watered control, nor did it return to the control rate when the plant was rewatered.
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TL;DR: The FAO crop model AquaCrop as mentioned in this paper is a water-driven growth engine, in which transpiration is calculated first and translated into biomass using a conservative, crop-specific parameter: the biomass water productivity, normalized for atmospheric evaporative demand and air CO 2 concentration.
Abstract: This article introduces the FAO crop model AquaCrop. It simulates attainable yields of major herbaceous crops as a function of water consumption under rainfed, supplemental, deficit, and full irrigation conditions. The growth engine of AquaCrop is water-driven, in that transpiration is calculated first and translated into biomass using a conservative, crop-specific parameter: the biomass water productivity, normalized for atmospheric evaporative demand and air CO 2 concentration. The normalization is to make AquaCrop applicable to diverse locations and seasons. Simulations are performed on thermal time, but can be on calendar time, in daily time-steps. The model uses canopy ground cover instead of leaf area index (LAI) as the basis to calculate transpiration and to separate out soil evaporation from transpiration. Crop yield is calculated as the product of biomass and harvest index (HI). At the start of yield formation period, HI increases linearly with time after a lag phase, until near physiological maturity. Other than for the yield, there is no biomass partitioning into the various organs. Crop responses to water deficits are simulated with four modifiers that are functions of fractional available soil water modulated by evaporative demand, based on the differential sensitivity to water stress of four key plant processes: canopy expansion, stomatal control of transpiration, canopy senescence, and HI. The HI can be modified negatively or positively, depending on stress level, timing, and canopy duration. AquaCrop uses a relatively small number of parameters (explicit and mostly intuitive) and attempts to balance simplicity, accuracy, and robustness. The model is aimed mainly at practitioner-type end-users such as those working for extension services, consulting engineers, governmental agencies, nongovernmental organizations, and various kinds of farmers associations. It is also designed to fit the need of economists and policy specialists who use simple models for planning and scenario analysis.
1,329 citations
Cites background from "Leaf enlargement and metabolic rate..."
...…relations literature that leaf expansive growth is the most sensitive of plant processes to water stress, and that stomatal conductance and senescence acceleration are considerably less sensitive in comparison (Boyer, 1970; Hsiao, 1973; Bradford and Hsiao, 1982; Sadras and Milroy, 1996)....
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TL;DR: It is now established that the rate of C02 assimilation in the leaves is depressed at moderate water deficits, mostly as a consequence of stomatal closure, and carbon assimilation may diminish to values close to zero without any significant decline in mesophyll photosynthetic capacity.
Abstract: This review focuses on the effects of water deficits on photosynthesis and partitioning of assimilates at the leaf level. It is now established that the rate of C02 assimilation in the leaves is depressed at moderate water deficits, mostly as a consequence of stomatal closure. In fact, depending on the species and on the nature of dehydration, carbon assimilation may diminish to values close to zero without any significant decline in mesophyll photosynthetic capacity. This remarkable resistance of the photosynthetic apparatus to water deficits became apparent after the measurement of photosynthesis at saturating C02 concentrations was made possible. Whenever light or heat stress are superimposed a decline in mesophyll photosynthesis may occur as a result of a 'down-regulation' process, which seems to vary among genotypes. A major secondary effect of dehydration on photosynthetic carbon metabolism is the change in partitioning of recently fixed carbon towards sucrose, which occurs in a number of species in parallel to the increase in starch breakdown. This increase in compounds of low molecular weight may contribute to an osmotic adjustment. Controlling mechanisms involved in this process deserve further investigation.
1,093 citations
TL;DR: In this article, the authors discuss N dynamics in soil plant systems, and outline management options for enhancing N use by annual crops, including livestock production with cropping, to improve N efficiency in agriculture.
Abstract: Nitrogen is the most limiting nutrient for crop production in many of the world's agricultural areas and its efficient use is important for the economic sustainability of cropping systems Furthermore, the dynamic nature of N and its propensity for loss from soil‐plant systems creates a unique and challenging environment for its efficient management Crop response to applied N and use efficiency are important criteria for evaluating crop N requirements for maximum economic yield Recovery of N in crop plants is usually less than 50% worldwide Low recovery of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, denitrification, and plant canopy Low recovery of N is not only responsible for higher cost of crop production, but also for environmental pollution Hence, improving N use efficiency (NUE) is desirable to improve crop yields, reducing cost of production, and maintaining environmental quality To improve N efficiency in agriculture, integrated N management strategies that take into consideration improved fertilizer along with soil and crop management practices are necessary Including livestock production with cropping offers one of the best opportunities to improve NUE Synchrony of N supply with crop demand is essential in order to ensure adequate quantity of uptake and utilization and optimum yield This paper discusses N dynamics in soil‐plant systems, and outlines management options for enhancing N use by annual crops
1,083 citations
722 citations
TL;DR: Results are interpreted as the signature of a transition from source to sink growth limitation under water deficit, suggesting release of the influence of C availability on sink organ growth.
Abstract: In plants, carbon (C) molecules provide building blocks for biomass production, fuel for energy, and exert signalling roles to shape development and metabolism. Accordingly, plant growth is well correlated with light interception and energy conversion through photosynthesis. Because water deficits close stomata and thus reduce C entry, it has been hypothesised that droughted plants are under C starvation and their growth under C limitation. In this review, these points are questioned by combining literature review with experimental and modelling illustrations in various plant organs and species. First, converging evidence is gathered from the literature that water deficit generally increases C concentration in plant organs. The hypothesis is raised that this could be due to organ expansion (as a major C sink) being affected earlier and more intensively than photosynthesis (C source) and metabolism. How such an increase is likely to interact with C signalling is not known. Hence, the literature is reviewed for possible links between C and stress signalling that could take part in this interaction. Finally, the possible impact of water deficit-induced C accumulation on growth is questioned for various sink organs of several species by combining published as well as new experimental data or data generated using a modelling approach. To this aim, robust correlations between C availability and sink organ growth are reported in the absence of water deficit. Under water deficit, relationships weaken or are modified suggesting release of the influence of C availability on sink organ growth. These results are interpreted as the signature of a transition from source to sink growth limitation under water deficit.
620 citations
Cites background from "Leaf enlargement and metabolic rate..."
...Proceedings of the National Academy of Sciences, USA...
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...The maintenance of photosynthesis under water deficit has been repeatedly reported (Boyer, 1970b; Quick et al., 1992; Bogeat-Triboulot et al., 2007)....
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...In contrast, water deficit strongly reduces leaf or shoot expansion rates (Boyer, 1970a; Hsiao, 1973; Ben Haj Salah and Tardieu, 1997; Tardieu et al., 1999, 2000)....
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TL;DR: * Supported by grants G 24052 and GE 3612 from the National Science Foundation.
Abstract: * Supported by grants G 24052 and GE 3612 from the National Science Foundation. 1 Beauchesne, G., M. Leboeuf, and R. Goutarel, in Regulateurs Naturels de la Croissance Vegtale (Paris: Centre National de la Recherche Scientifique, 1964), p. 119. 2 Letham, D. A., in Regulateurs Naturels de la Croissance Vegetale (Paris: Centre National de la Recherche Scientifique, 1964), p. 109; and ref. 6 (below). 3Miller, C. O., these PROCEEDINGS, 47, 170 (1961); and refs. 13 and 16 (below). 4Letham, D. S., and C. 0. Miller, Plant Cell Physiol., in press. 6 Letham, D. S., J. S. Shannon, and I. R. McDonald, Proc. Chem. Soc., 1964, 230. 6 Letham, D. S., Life Sci., 2, 569 (1963). 7 Kefford, K. P., Science, 142, 1495 (1963). 8 Miller, C. O., in Modern Methods of Plant Analysis (Berlin: Springer-Verlag, 1963), vol. 6, p. 194. 9 McCalla, D. R., D. J. Moore, and D. Osborne, Biochim. Biophys. Acta, 55, 522 (1962). 10 Hurlbert, R. B., H. Schmitz, A. F. Brumm, and V. R. Potter, J. Biol. Chem., 209, 23 (1954). 11 Jacobson, K. B., Science, 138, 515 (1962). 12 Khym, J. X., and W. E. Cohn, J. Am. Chem. Soc., 76, 1818 (1954). 13 Miller, C. O., Plant Physiol., 37, xxxv (1962). 14 Loeffier, J. E., and J. Van Overbeek, in Regulateurs Naturels de la Croissance V~ggtale (Paris: Centre National de la Recherche Scientifique, 1964), p. 77. 15 Fox, J. E., Plant Physiol., 39, xxxi (1964). 16 Miller, C. O., and F. H. Witham, in Rlgulateurs Naturels de la Croissance V~ggtale (Paris: Centre National de la Recherche Scientifique, 1964), p. I (erratum).
343 citations
TL;DR: It was concluded that leaves are not in equilibrium with the potential of the water which is absorbed during growth, and the nonequilibrium is brought about by a resistance to water flow which requires a potential difference of 1.5 to 2.5 bars in order to supply water at the rate necessary for maximum growth.
Abstract: A thermocouple psychrometer that measures water potentials of intact leaves was used to study the water potentials at which leaves grow Water potentials and water uptake during recovery from water deficits were measured simultaneously with leaves of sunflower (Helianthus annuus L), tomato (Lycopersicon esculentum Mill), papaya (Carica papaya L), and Abutilon striatum Dickson Recovery occurred in 2 phases The first was associated with elimination of water deficits; the second with cell enlargement The second phase was characterized by a steady rate of water uptake and a relatively constant leaf water potential Enlargement was 70% irreversible and could be inhibited by puromycin and actinomycin D During this time, leaves growing with their petioles in contact with pure water remained at a water potential of -15 to -25 bars regardless of the length of the experiment It was not possible to obtain growing leaf tissue with a water potential of zero It was concluded that leaves are not in equilibrium with the potential of the water which is absorbed during growth The nonequilibrium is brought about by a resistance to water flow which requires a potential difference of 15 to 25 bars in order to supply water at the rate necessary for maximum growthLeaf growth occurred in sunflower only when leaf water potentials were above -35 bars Sunflower leaves therefore require a minimum turgor for enlargement, in this instance equivalent to a turgor of about 65 bars The high water potentials required for growth favored rapid leaf growth at night and reduced growth during the day
343 citations
TL;DR: It was concluded that moderately low leaf water potential affects photosynthesis in at least two ways: first, through an inhibition of oxygen evolution by chloroplasts and, second, by closure of stomata in intact leaves.
Abstract: Chloroplasts were isolated from pea and sunflower leaves having various water potentials. Oxygen evolution by the chloroplasts was measured under identical conditions for all treatments with saturating light and with dichloroindophenol as oxidant. Evolution was inhibited when leaf water potentials were below -12 bars in pea and -8 bars in sunflower and the inhibition was proportional to leaf water potential below these limits. Inhibition was more severe in sunflower than in pea chloroplasts. In sunflower, it could be detected after 5 minutes of leaf desiccation, and, up to 1 hour, the effect was independent of the duration of low leaf water potential.In high light, the reduction in activity of sunflower chloroplasts paralleled the reduction in CO(2) fixation by intact sunflower plants having low leaf water potentials. Stomatal apertures and transpiration rates were also reduced under these conditions and were probably limiting. In low light, intact sunflowers required more light per unit of CO(2) fixed when leaf water potentials were low than when they were high. This increased light requirement in the intact system was of a magnitude which could be predicted from the reduced oxygen evolution by the isolated chloroplasts. It was concluded that moderately low leaf water potential affects photosynthesis in at least two ways: first, through an inhibition of oxygen evolution by chloroplasts and, second, by closure of stomata in intact leaves.
142 citations
TL;DR: Over long periods of treatment in a variety of osmotica the threshold value for extensibility and growth is seen to fall to lower values to permit resumption of growth at reduced turgor.
Abstract: The view that the plant cell grows by the yielding of the cell wall to turgor pressure can be expressed in the equation: rate = cell extensibility × turgor. All growth rate responses can in principle be resolved into changes in the 2 latter variables. Extensibility will relate primarily to the yielding properties of the cell wall, turgor primarily to solute uptake or production. Use of this simple relationship in vivo requires that at least 2 of the 3 variables be measured in a growing cell. Extensibility is not amenable to direct measurement. Data on rate and turgor for single Nitella cells can, however, be continuously gathered to permit calculation of extensibility (rate/turgor). Rate is accurately obtained from measurements on time-lapse film. Turgor is estimated in the same cell, to within 0.1 atm or less, by measurement of the ability of the cell to compress gas trapped in the closed end of a capillary the open end of which is in the cell vacuole. The method is independent of osmotic equilibrium. It operates continuously for several days, over a several fold increase in cell length, and has response time of less than one minute. Rapid changes in turgor brought on by changes in tonicity of the medium, show that extensibility, as defined above, is not constant but has a value of zero unless the cell has about 80% of normal turgor. Because elastic changes are small, extensibility relates to growth. Over long periods of treatment in a variety of osmotica the threshold value for extensibility and growth is seen to fall to lower values to permit resumption of growth at reduced turgor. A brief period of rapid growth (5× normal) follows the return to normal turgor. All variables then become normal and the cycle can be repeated. The cell remains essentially at osmotic equilibrium, even while growing at 5× the normal rate. The method has potential for detailed in vivo analyses of “wall softening.”
128 citations
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