- Usualy, depend on the plant species, in cocoa tree above a photon irradiance level of 600- 700 umol photons, the carbono dioxide fixition sensible reduce due to stomata cosing.
The phosynthetic efficiency is the fraction of light energy converted into chemical energy, so I would say that it depends where (for which irradiance) would you define it. At low irradiance A has a higher efficiency (probably adapted to shadow); at high B has higher efficiency (probably adapted to high light), and C has a lower efficiency than the other two at any irradiance (proably more versatile).
Blackman roof ceiling formalism in early 1905 describes light response in two terms slope and saturation. Later Evans and Ogren in Planta introduced a curvature factor teta, but neither use the term efficiiency that is the first derivative of the curve, a variable on light. This character depends on what level of light tou inean. Roof is maximal quantum yield and ceiling is the saturation level.. The reverse of maximal quantum yield is quantum requirement. http://www.life.illinois.edu/govindjee/photosynBook/Chapter6.pdf
The higher level of CO2 absortion is at point A. But it is also depending of leaf age and
the leaf positionin the plant foliage in relation to sun irradiation.
Does B has better photosynthetic efficiency at low light than A and C?
The slope is actually the first derivative of Y versus X. Please take in mind tha absorbed fluence and not irradiance is the convenienet unit. Other limiting factors apart from light should be equal among cases, like with saturating CO2 in an oxugen electrode or in a PAM fluorimeter or stomata may regulate light response.
a curve has got a variable slope. The slope is called efficiency. Blackman put in evidence that plants gross photosynthesis response to light was descrbed by 2 parameters the initial slope and the tangent to saturation. You may well have high values for the first and low for the tangent as in most of shade plants.
C should be the lowest one. But I am not sure abut A and B. We have to think about light environment.
If these curves are the response of single leaf, for the whole plant may be different.
The photosynthetic efficiency is actually the fraction of light energy converted into chemical energy during photosynthesis in plants and algae. However, in the cases of the efficiency it depends on how light energy is defined thus depending on whether we count only the light that is absorbed, and on what kind of light is used. For actual sunlight, where only 45% of the light is in the photosynthetically active wavelength range, the theoretical maximum efficiency of solar energy conversion is approximately 11%. In actuality, however, plants do not absorb all incoming sunlight (due to reflection, respiration requirements of photosynthesis and the need for optimal solar radiation levels) and do not convert all harvested energy into biomass, which results in an overall photosynthetic efficiency of 3 to 6% of total solar radiation. in the cases of the graph, A has high efficiency than B at low irradiance, however B has high efficiency at high irradiance than A with the least efficiency at C in any irradiance.
It is possible, that these A,B,C, are as follows: A optimal photosynthesis,B Dynamic photo inhibition in moderate excess light,C ,chronic photo inhibition in high excess light.
The quantum yield of radiation is in the order of B>A>C at low irradiance level but at higher light its in the order A>B>C. Since B is efficient at lower light level (higher slope in the beginning), it is a typical light response curve for a shade adapted plant. C of course represents the least efficient. However A is more efficient at higher irradiance level.
may i ask another question here? if i m allowed, is there any general slop pattern to distinguish between herbs and trees?herbs having smaller slope compared with tress for instance???
Guido Bongi Would you please give me the reference about your comment ``Blackman put in evidence that plants gross photosynthesis response to light was described by 2 parameters the initial slope and the tangent to saturation``. I am very much interested to learn more about this.
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