Rate of Photosynthesis

5 Key excerpts on "Rate of Photosynthesis"

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  eBook - PDF

  Physiology of Crop Production

  • N.K. Fageria, V.C. Baligar, Ralph Clark(Authors)
  • 2006(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 4 Photosynthesis and Crop Yield INTRODUCTION Photosynthesis is the basic process underlying plant growth and production of food, fuel, and fiber required to sustain life (Tolbert, 1997). An understanding of photosynthesis is therefore necessary to appreciate processes that determine yield in agriculture, forestry, ecology, and many other fields. This most important biochemical process in green plants, which literally means building by light, prob-ably evolved 3500 million years ago (Shopf, 1993). In general, pho-tosynthesis is the process by which plants synthesize organic com-pounds from inorganic substances using light. During photosynthesis, C from atmospheric carbon dioxide (CO 2 ) is fixed to become part of many organic molecules that constitute plant tissues. Because of this, total dry matter production of crop plants is correlated with photo-synthetic rates integrated over plant growth cycles. Yield is related to total dry matter for many plants, especially associations with harvest index (see Chapter 3). Light energy is converted into chemical potential energy when processes of photosynthesis occur. Chemical products of photosyn-thesis are translocated to sites of utilization and are incorporated into plant parts of economic interest such as grain in annual crops. Effi-ciency of light energy conversion to economic products depends on various factors such as C 0 2 supply, light intensity, light interception, soil fertility level, water availability, temperature, and genetic factors related to the plant itself (Berry and Bjorkman, 1980; Eastin and Sullivan, 1984). Detailed discussion of these factors has been pro-vided by Moss (1984). In photochemical reactions, carbohydrates are produced, and 0 2 and water are released according to the following equation: 95

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  eBook - ePub

  Stress Physiology of Woody Plants

  • Wenhao Dai(Author)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  2 assimilation in chilling-tolerant C4 plants at temperatures < 20°C; however, it is uncertain that Rubisco capacity is still the limiting factor when temperatures are elevated. Sage and Kubien’s review (2007) pointed out that a better understanding of plant response to temperature stress will put us in a better position to predict and mitigate the effects of global climatic change on photosynthesis in higher plants.

  3.3  Respiration

  Plants need energy and carbon skeletons to sustain their growth and development. As discussed in the previous part of this chapter, plants capture and convert light energy into chemical energy through photosynthesis. The captured energy is stored in the plant as complex compounds, such as sugar, starch, protein, etc. The process plants use to release energy is called respiration.

  3.3.1  Aerobic respiration

  Aerobic respiration is expressed as:

  C 6 H 12 O 6 + 6 O 2 + 6 H 2 O → 6 CO 2 + 12 H 2 O + Energy   36   ATP

  In aerobic respiration, the organic molecule glucose is oxidized to release energy (ATP) in the presence of O2 . The O2 itself is reduced to form H2 O, and the carbon atoms of glucose are released as CO2 . The energy released from respiration is available to the plant in the form of adenosine triphosphate (ATP) that is involved in almost all biological processes in living plant cells.

  There are four major stages in the aerobic respiration process. The first stage is glycolysis in which one 6C-glucose is split into two 3C-pyruvates. Glycolysis occurs in the cytosol and can be seen in all living cells. In plants, glucose is derived from sucrose (12C) and other carbohydrates, such as starch. A series of enzymes are involved in the process of glycolysis (Figure 3.2

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  eBook - PDF

  Aquatic Photosynthesis

  Second Edition

  • Paul G. Falkowski, John A. Raven(Authors)
  • 2013(Publication Date)
  • Princeton University Press

    (Publisher)

  We strive here to examine the phenomenology of the short-term photosyn- thetic responses to variations in the aquatic environment. In the following chapter we examine the long-term changes and biogeochemical feedbacks that involve aquatic photosynthetic organisms. Let us begin with a brief look at how aquatic ecologists measure photosynthesis in nature and then consider acclimation responses within the framework of what we have learned in the earlier chapters. Estimating Photosynthesis in Aquatic Ecosystems Plant physiologists define the term gross photosynthesis, P g , as the light- dependent rate of electron flow from water to terminal electron acceptors (e.g., CO 2 ) in the absence of any respiratory losses (Lawlor 2001). It follows that this definition of P g is directly proportional to linear photosynthetic electron trans- port and, hence, gross oxygen evolution. 2 Gross photosynthesis accounts for all photosynthetic carbon fixation, whether the organic carbon formed becomes part of the organism or is excreted or secreted into the environment as organic carbon or is respired to CO 2 ; however, the relationship between gross oxygen evolution and CO 2 fixation will be modified by the photosynthetic quotient (see chapter 8). Respiratory losses in photosynthetic organism(s) can be defined as the rate of electron flow from organic carbon to O 2 (or, in the case of anaerobic photo- synthetic bacteria, to another electron acceptor) with the concomitant produc- tion of CO 2 . This definition includes all metabolic processes that contribute to 320 | Chapter 9 2 It should be noted that gross photosynthesis should be defined on the basis of oxygen evolution rather than carbon fixation. This difference is critical, especially if photorespiratory rates are high.

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  Photosynthesis V2

  Development, Carbon Metabolism, and Plant Productivity

  • Govindjee, Unknown Govindjee(Authors)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  (Chapter 11) and by Christy Porter (Chapter 14) (this volume). With the exception of minor updating, this chapter is based on literature avail-able to the authors up to May 1980—Editor. 419 Photosynthesis: Development, Carbon Metabolism, and Plant Productivity, Vol. II Copyright © 1982 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN: 0-12-294302-3 420 ROGER Μ. GIFFORD AND COLIN L. D. JENKINS CER Carbon dioxide exchange rate per unit leaf area CGR Crop growth rate per unit ground area Chi Chlorophyll DW Dry weight LAD Leaf area duration, meaning the area under a plot of LAI against time LAI Leaf area index, meaning the leaf area per unit ground area SLW Specific leaf weight, meaning leaf DW per unit leaf area RuBP Case Ribulosebisphosphate carboxylase HPMS α-Hydroxypyridinemethanesulfonic acid HBA 2-Hydroxy-3-butynoic acid MeHBA Methyl 2-hydroxy-3-butynoate BuHBA Butyl 2-hydroxy-3-butynoate INH Isonicotinyl hydrazide P A L P Pyridoxal phosphate PCO Photosynthetic carbon oxidation PCR Photosynthetic carbon reduction ABSTRACT Crop photosynthesis is a hierarchical process, and its rate can be separated into capaci-ty and intensity components. Crop photosynthetic capacity can be improved by man-agement strategies, which extend the persistence of the leaf cover for as much of the year as possible, and by ensuring rapid attainment of full interception of the incoming solar radiation by leaves after leaf canopy development starts. Although there are circumstances where crop growth rate can suffer due to too high a leaf area, the concept of optimum leaf area index has not yet proved to be a useful management criterion. For C 3 -crops in tropical environments, there may be some scope to improve productivity by having up-right-leaved canopies, but for most situations modification of canopy architecture has little to offer.

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  eBook - ePub

  Biophysical Ecology

  • David M. Gates(Author)
  • 2012(Publication Date)
  • Dover Publications

    (Publisher)

  3 -type plants have photorespiration.

  It has been shown by Decker (1959), Holmgren and Jarvis (1967), Hew et al. (1969), and Jackson and Volk (1970) that photorespiration increases with increasing light intensity. Hofstra and Hesketh (1969) indicate that the temperature dependence of photorespiration probably follows the temperature response of photosynthesis, although according to Jackson and Volk (1970), this may not be true at temperatures above the photosynthetic optimum. Photorespiration increases with increasing oxygen concentration according to Forrester et al. (1966).

  Internal CO 2 Concentration

  If one measures net photosynthetic rate as a function of carbon dioxide concentration in the air outside a leaf, conversion of this function to that relating photosynthesis to carbon dioxide concentration in the intercellular air spaces inside the leaf is straightforward. The procedure involves measuring the rate of loss of water vapor, or the transpiration rate E , and deriving the water-vapor resistance r e as given by

  (14.22)

  when the leaf temperature

  T

  , air temperature T a , and relative humidity h are measured. The quantity s d (

  T

  ) is the water-vapor density at saturation as a function of leaf temperature, and s d a (T a ) is the water-vapor density of the air at saturation as a function of air temperature. Since all quantities except r are known, one can solve for r . (This analysis depends on the air movement across the leaf surface being vigorous enough to reduce the boundary-layer resistance to a small value.) When r for water vapor is determined, this value then gives the resistance R 1 to carbon dioxide since R 1 = 1.56r . The quantity 1.56 is the ratio of the diffusion coefficients of H2 O and CO2

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