[Jeff Kropp]

...The rates of net photosynthesis showed a significant quadratic regression with the tissue P concentration, which might resemble the action curve of mineral nutrients. ...The lack of stimulation of net photosynthesis with increasing tissue P could be due either to a deficiency in other mineral elements such as N, or to an intrinsic inability to use the excess of nutrients. The decline in net photosynthesis when the tissue P concentration exceeded 0.45% DM could be interpreted as a toxicity process.

Seems to support my observations. They speculate an N limitation but do not note any N related data. Without N data I don't think they can make a case for P "toxicity", although their paper supports a premise that too much P is detrimental to some species.

Back when I was running a P limited tank I did notice an ability to produce a lot of pearling with almost no growth. Although I don't have a diagram showing the bio-chemical process of photosynthesis at hand, my layman's observations suggest that N is used in photosynthesis, while P is involved in cellular construction and K with cellular maintainance. Could pearling be used as a subjective indicator of N availability if only pH and dKH are known?

Jeff

 

[Jeff Kropp]

Production of O2 is considered growth from plants, algae in aquatic ecosystems, more O2=> more growth and oprimary production.
Even if your eye cannot tell where the growth is occuring, if the plants are fixing carbon, they will produce O2.
More Carbon fixed, more O2.

I did a little searching on the web for a photosynthesis flow diagram. No luck but I did run across mention of a Calvin cycle? A dark phase reaction that coverts collected C into sugars? It seemed to involve some form of P. If there was insufficient P to process all the light phase C gathered would a plant then release excess C as CO2 during the dark phase? I think I recall a large pH swing with my strong pearling, low growth, P limited observation. With P supplementation my pH swings seem minimal.

Where does N enter the biochemical process of plants?

Jeff

 

[Jeff Kropp]

I'll put my two bits in here anyway.

Ah Ha! a plausible explanation. We are two bits richer.

But wait... in the linked diagram, CO2 is going into the "dark box"! I thought it was used during the light phase?
___
Jeff