Light compensation point

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The light compensation point of a plant indicates the illuminance at which the carbon dioxide fixed by the Calvin cycle and the carbon dioxide excreted during its respiration are quantitatively equal. The illuminance indicates how much photosynthetically usable light, i.e. photons of the wavelengths 400 to 700 nm per area and time, hit the plants (µmol · m −2 · s −1 ).

This can also be related to the oxygen turnover: the light intensity, at which the oxygen consumption through the breathing of a plant and the oxygen production through photosynthesis are balanced, is the light compensation point.

If this point is exceeded, there is a net gain in carbon fixation (net photosynthesis). In the long term, the plant can only survive at illuminance levels above the compensation point.

Dependence of the photosynthesis rate (ordinate) on the amount of light available (abscissa) in sun and shade plants . The light saturation point is reached much faster by shade plants, their light compensation point is also lower. Net photosynthesis takes place in the positive area of ​​the ordinate, while net respiration occurs in the negative area.

The light compensation point allows you to distinguish between sun plants and shade plants . While in sun plants the light compensation point is only reached at a relatively high illuminance, shadow plants can already show a net gain in carbon fixation at lower illuminance. The light compensation point for a sun leaf is 20–30 µmol · m −2 · s −1 , for a shadow leaf it is less than 10 µmol · m −2 · s −1 .

With C 4 plants the illuminance at the light compensation point is higher than with C 3 plants , so they need significantly more light than C 3 plants in order to exist. However, at high illuminance levels, they are far superior to the C 3 plant plants in terms of their rate of photosynthesis. Under natural conditions, C 4 plants do not reach their light saturation point, so they are usually light-limited. Only when a severe lack of water causes the plant to largely or completely close its stomata, and as a result there is a lack of CO 2 , are they CO 2 limited.

See also

literature

  • Lüttge, Ulrich; Kluge Manfred and Bauer, G .: Botany . 5th edition. Wiley-VCH, Weinheim 2005, ISBN 978-3-527-31179-8 .

supporting documents

  1. ↑ Katharina Munk: Botany . Thieme, 2008; ISBN 978-3131448514 , p. 263
  2. ↑ Linder Biologie Complete Volume, Schroedel, 22nd edition, Braunschweig, 2005, p. 56
  3. ↑ Joachim W. Kadereit, Christian Körner, Benedikt Kost, Uwe Sonnewald: Strasburger, Textbook of Plant Sciences, 37th edition, 2014, Springer-Spektrum, doi : 10.1007 / 978-3-642-54435-4 , page 396