Jeff Kropp· Registered
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.plantbrain said:...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.
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?