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I wasn't around for the start of this topic, but I'll put my two bits in here anyway. I suspect that I've seen the same thing that Jeff saw. In an apparently phosphate-limited tank the plants can bubble daily while there is little observable increase in plant mass. The plants are sometimes stunted.
Oxygen is evolved in step one of the photosynthetic reactions -- using Tom's UC Davis link -- but free phosphate isn't required in the reaction until ATP is produced from ADP and P in the last step of the thylkaloid membrae process.
Carbon isn't actually fixed in the photosynthetic process until you get to the dark reactions. There CO2 is combined with a simple sugar phosphate. Phosphates are not only required in the initial reactants but also required in the form of ATP later on in the process.
The page at
http://www.lions.odu.edu/~knesius/miniunits/epsilon/epsilon12.html
Provides a pretty simple diagram of the overall process, plus some details of the dark reactions.
There are a lot of steps involved between the point where O2 is evolved in the reaction to the point where free phosphate is required in large amounts. It looks to me like under pathologic conditions it should be possible to get O2 evolved without there being any actual growth.
Phosphate is essential to a lot of reactions in a plant. I read somewhere that under phosphate deficient conditions a plant can move phosphate from less essential roles to reactions where it is more necessary. I can easily imagine that a plant suffering a phosphorus shortage might shift its limited supply out of the Calvin cycle and into the Krebs cycle. The plant dies if the Krebs cycle shuts down. It can survive for a while without the products of the Calvin cycle.
Roger Miller
Oxygen is evolved in step one of the photosynthetic reactions -- using Tom's UC Davis link -- but free phosphate isn't required in the reaction until ATP is produced from ADP and P in the last step of the thylkaloid membrae process.
Carbon isn't actually fixed in the photosynthetic process until you get to the dark reactions. There CO2 is combined with a simple sugar phosphate. Phosphates are not only required in the initial reactants but also required in the form of ATP later on in the process.
The page at
http://www.lions.odu.edu/~knesius/miniunits/epsilon/epsilon12.html
Provides a pretty simple diagram of the overall process, plus some details of the dark reactions.
There are a lot of steps involved between the point where O2 is evolved in the reaction to the point where free phosphate is required in large amounts. It looks to me like under pathologic conditions it should be possible to get O2 evolved without there being any actual growth.
Phosphate is essential to a lot of reactions in a plant. I read somewhere that under phosphate deficient conditions a plant can move phosphate from less essential roles to reactions where it is more necessary. I can easily imagine that a plant suffering a phosphorus shortage might shift its limited supply out of the Calvin cycle and into the Krebs cycle. The plant dies if the Krebs cycle shuts down. It can survive for a while without the products of the Calvin cycle.
Roger Miller
