I have taken IRGA reading of rice leaf. Its showing low photosynthesis. What should be the expected outcome for Light compensation point, Dark respiration and Quantum yield?
I guess doing a whole light response curve will answer all your questions
Of course, you have to build the whole curve Photosynthesis vs PAR (Photosinthetic active radiation) and then you can get the parameters you are looking for! You can get this curve changing PAR intensity from darkness to high level say 1200 or 1500 umol m-2 s-1, in steps for example for the first 0-300 umol m-2 s-1 every 50 umol m-2 s-1 and after every 100. In every step you have to wait until readings in your irga are stable.
...and after that you'll still have to fit a nonlinear function to estimate your parameters... that might be the hardest part.
Not so hard, it is well know that the relationship is a hyperbolic function as follow
P = ((aPAR)/((b + PAR)) + c where P is the photosynthesis and a, b and c are the parameters of the curve that you can get with any computer program as curfit. You can get the compensation point when P = 0, and when PMax = a you get stauration point ; and more parameters as sensitivity for example. If this is so complicated, get the data, send them to me and I will get this parameters for you.
But there are variations of the equation, and I think the actual relationship is far from being established. Asymptotic functions for example do not account for photoinhibition, or at least are not able to model the relationship after Pmax.
Here's just some articles the OP might be interested in are:
Physiological response curve analysis using nonlinear mixed models, Peek et al. 2002
The statistical analysis of ecophysiological response curves obtained from experiments involving repeated measures, Potvin et al. 1990
The boreal dwarf shrub Vaccinium vitis-idaea retains its capacity for photosynthesis through the winter, Lundell et al. 2008. (who used a nonrectangular hyperbolic function)
and many more which I can't find now...
But basically yes, functions of that form are used.
I think there is no problem if the points distribution do not fit a hyperbolic function. Fortunately, the curfit program can cope with any type of curve, and if we know about the constants, then the problem is solved. My offer about to fit the best function to the data is still opened!
Photosynthesis as a function of light is important criteria. Therefore your measurements conditions need to be checked. Low photosynthesis most probably result in low respiration in actively growing leaves however, generally low photosynthesis accompanied with high rate of dark respiration in aged/senescence set leaves.
PS II activity is depends on light intensity and health of pigment:protein complexes some time not related to net photosynthesis. But the ETR may be related to net assimilation if stomatal and other mesophyll functions are not inhibited.
I happened upon one more model when rummaging through papers, it's a (non-asymptotic) modified exponential model by Chen et al. 2011, that seems to be able to predict light-saturated values quite closely to the original measurements, and thus give some more realistic values about the light saturation point and Amax:
http://link.springer.com/article/10.1007%2Fs11099-011-0056-5
- Badges
- Science topic
- Similar topics
- Biological Science
- Biochemistry
- Enzymology
- Enzymes