CO 2 compensation point

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The CO 2 compensation point (Γ) of a plant indicates the carbon dioxide concentration above which, especially in the intercellular areas of the leaf , the CO 2 uptake ( photosynthesis ) and CO 2 release ( respiration , photorespiration ) are in equilibrium. Above this value, there is a net photosynthesis and thus a gain in carbon. Breathing predominates, so that the plant loses carbon in its balance sheet. There is therefore no net CO 2 flow in equilibrium.

Γ depends strongly on the temperature and the path of the CO 2 fixation from ( C 3 - or C 4 -Pflanze ).

background

Dependence of the photosynthesis rate on the amount of CO 2 in the air for C 3 (green) or C 4 plants (red). The CO 2 compensation point Γ is the point of intersection with the abscissa . This is lower for C 4 plants than for C 3 plants.

Photosynthesis depends on a number of abiotic factors that also influence one another. The law of the minimum applies : if one of the factors becomes limiting, it throttles the entire system.

One of these factors is the CO 2 concentration, as carbon dioxide is fixed in photosynthesis. Provided that the amount of light is high enough and does not itself become a limiting factor, it has been observed that the photosynthetic output increases when the CO 2 concentration in the surrounding atmosphere is increased. This process is limited - the photosynthesis rate follows a saturation curve so that no increase is observed at sufficiently high concentrations. Conversely, the carbon dioxide release from respiration and photorespiration exceeds the CO 2 fixation of photosynthesis if the CO 2 concentration drops too much. The point at which both processes take place in equilibrium is called the CO 2 compensation point.

For the consideration of the CO 2 dependency the internal CO 2 concentration of the leaf, especially in the intercellular ones, is decisive. This of course depends on the atmospheric CO 2 concentration as well as various internal plant factors.

C 3 plants

For most of the higher plants the CO 2 compensation point is between 30 and 60 µl / l (corresponds to around 10–20% of the natural CO 2 concentration in the air, around 0.005–0.010% by volume of CO 2 ). Saturation is reached at around 0.05-0.10% by volume of CO 2 .

C 4 plants

C 4 plants have an energy-driven, internal CO 2 enrichment mechanism. This means that the Γ values ​​of these plants are much lower than those of C 3 plants (<0.001% by volume)

meaning

The height of the CO 2 compensation point reflects the effectiveness of the photosynthetic output. If Γ is low, a CO 2 fixation is operated effectively against the release - the leaf thus shows a high affinity for CO 2 . In contrast, a high Γ means that the effectiveness of the CO 2 uptake is low.

With increasing temperatures, the effects of photorespiration in C 3 plants come into play, which reduce the carbon gain. Compared to C 3 plants, especially at temperatures above 25 ° C, C 4 plants enjoy an ecophysiological advantage due to the active CO 2 enrichment . Therefore, they are far more common than C 3 plants in warm and hot climates .

See also

literature

  • Peter Schopfer, Axel Brennicke: Plant Physiology . 7th edition, Spektrum Akademischer Verlag, 2010, ISBN 978-3827423511 , pp. 257 f.
  • Ulrich Lüttge, Manfred Kluge: Botany - The introductory biology of plants . 6th updated edition, Wiley-VCH, 2012, ISBN 978-3527331925 , p. 497 ff.
  • Katharina Munk: botany . Thieme, 2008; ISBN 978-3131448514 , p. 264.

supporting documents

  1. ↑ Peter Schopfer and Axel Brennicke: Plant Physiology . 7th edition, Spektrum Akademischer Verlag, 2010, ISBN 978-3827423511 , p. 258.
  2. ↑ Ulrich Lüttge and Manfred Kluge: Botany - The introductory biology of plants . 6th updated edition, Wiley-VCH, 2012, ISBN 978-3527331925 , p. 497.
  3. ↑ a b Ulrich Lüttge, Manfred Kluge: Botany - The introductory biology of plants . 6th updated edition, Wiley-VCH, 2012, ISBN 978-3527331925 , p. 498.