Hi Santoshkumar,

you would surely understand better looking at a light-response curve of photosintesis. To sum up, in the dark there is no photosynthetic carbon assimilation, and CO2 is released by leaves because of respiration . Thus, CO2 assimilation could be considered negative in this part of the curve.

As the photon flux increases, photosynthetic CO2 assimilation increases as well until it equals CO2 release by mitochondrial respiration. The point at which CO2 uptake balances CO2 release is called the light compensation point.

Increasing photon flux above this point results in a proportional increase in photosynthetic rate, represented by a linear relationship between photon flux and photosynthetic rate. In this part photosynthesis is light limited, so the more light is incident the more photosynthesis comes about. In this linear portion of the curve, the slope of the line reveals the maximum quantum yield of photosynthesis for a leaf.

At higher photon fluxes, the photosynthetic response to light starts to level off and reaches saturation, after which further increase in photon flux no longer affect photosynthetic rates, indicating that factors other than incident light, (electron transport rate, rubisco activity etc.) limit photosynthesis. After the saturation point, photosynthesis is referred to as CO2 limited, due to the inability of the Calvin cycle enzymes to keep pace with the absorbed light energy.

Of course compensation and saturation points are different based on the species and also within the leaves of a same plant. As you know, in order to study photosintesis in eucalyptus clones you should monitor the gas exchanges of leaves by proper instruments (IRGA) and build the above mentioned curves.

Best regards

Hi Santoshkumar,

you would surely understand better looking at a light-response curve of photosintesis. To sum up, in the dark there is no photosynthetic carbon assimilation, and CO2 is released by leaves because of respiration . Thus, CO2 assimilation could be considered negative in this part of the curve.

As the photon flux increases, photosynthetic CO2 assimilation increases as well until it equals CO2 release by mitochondrial respiration. The point at which CO2 uptake balances CO2 release is called the light compensation point.

Increasing photon flux above this point results in a proportional increase in photosynthetic rate, represented by a linear relationship between photon flux and photosynthetic rate. In this part photosynthesis is light limited, so the more light is incident the more photosynthesis comes about. In this linear portion of the curve, the slope of the line reveals the maximum quantum yield of photosynthesis for a leaf.

At higher photon fluxes, the photosynthetic response to light starts to level off and reaches saturation, after which further increase in photon flux no longer affect photosynthetic rates, indicating that factors other than incident light, (electron transport rate, rubisco activity etc.) limit photosynthesis. After the saturation point, photosynthesis is referred to as CO2 limited, due to the inability of the Calvin cycle enzymes to keep pace with the absorbed light energy.

Of course compensation and saturation points are different based on the species and also within the leaves of a same plant. As you know, in order to study photosintesis in eucalyptus clones you should monitor the gas exchanges of leaves by proper instruments (IRGA) and build the above mentioned curves.

Best regards

LS is the point above which an increase in photon flux produces no further increase in photosynthesis :)

Thanks a lot, dear Dr. Romano, Dr. Ali and Dr. Andrew for the valuable information you shared. Dr. Ali sir, you are correct, I am interested in both, the definition and the way of determination of light saturation in eucalyptus.