I was thumbing through a well known, but older Limnology text (Hutchinson, 1975, Vol 3 Limnological Botany pg 351-357) when I saw a nice graph showing growth rate vs NO3 concentration.
It seems Paul had found that 20 ppm N-NO3 and above was the ideal range for submersed plant growth(Vallisneria americana) back in the 1960's(1966). I suppose I redisocovered this range(20-75ppm) independently some 30 years later.
What is interesting is that we both arrived at the same range. At progressively high concentrations, this high rate of growth slowly decline, but very slowly.....even at 100ppm N-NO3 etc.
This also mirrors my own observations when I did longer term NO3 at 75ppm for several weeks.
What is really interesting is how rapid the growth rate increases when the level is maintained.
For example
N-NO3)
At 5 ppm the rate of growth is greatly reduce, about 2.2/0.7= 3.14 times less growth (dry weight mass).
At 10ppm, the growth was about 1/2, 2.2/1.1 = 2x less growth than at 20-80ppm.
After 20ppm, the plant's growth is no longer nitrogen limited.
Fast forward to the molecular age of plant biology.
Why might these plants show this pattern? How would they control it?
Given what is known about LAT and HAT transportors for NO3, it may now be suggested that when plants have all their constitutive and inducible transporters upregulated and maintained, they grow faster and have non limited growth.
In order for the plants to do this, 20-30ppm of N-NO3 needs to be present in the medium(the water column). Now we have a plant that is healthy and can grow at a maximum rate. If the NO3 levels varies between say 2-15ppm, then the various transporters will be degraded and more efficient transports(the HATs) specific to low N-NO3 levels will be put in their place. As a result, the plants growth rate will be reduced.
It takes more energy to concentrate nutrients when there is less in the external environment. So at higher levels, the plants use different transportors that take full advantage of the higher N-NO3 levels and grow faster as result.
Which is about what we find to be optimal for growth in the water column.
Seems the data was and has been there all along, just no one bothered to listen to Paul, nor look stuff up.
He looked at many lakes and plants and did a lot of tissue analysis beside this as well.
Reference:
Gerloff, G.C., and Krombholz, P.H., 1966. Tissue analysis as measure of nutrient availability for the growth of aquatic plants. Limnological Oceanography, 11:529-537. (Hutchinson, 351-357)
Regards,
Tom Barr
It seems Paul had found that 20 ppm N-NO3 and above was the ideal range for submersed plant growth(Vallisneria americana) back in the 1960's(1966). I suppose I redisocovered this range(20-75ppm) independently some 30 years later.
What is interesting is that we both arrived at the same range. At progressively high concentrations, this high rate of growth slowly decline, but very slowly.....even at 100ppm N-NO3 etc.
This also mirrors my own observations when I did longer term NO3 at 75ppm for several weeks.
What is really interesting is how rapid the growth rate increases when the level is maintained.
For example
At 5 ppm the rate of growth is greatly reduce, about 2.2/0.7= 3.14 times less growth (dry weight mass).
At 10ppm, the growth was about 1/2, 2.2/1.1 = 2x less growth than at 20-80ppm.
After 20ppm, the plant's growth is no longer nitrogen limited.
Fast forward to the molecular age of plant biology.
Why might these plants show this pattern? How would they control it?
Given what is known about LAT and HAT transportors for NO3, it may now be suggested that when plants have all their constitutive and inducible transporters upregulated and maintained, they grow faster and have non limited growth.
In order for the plants to do this, 20-30ppm of N-NO3 needs to be present in the medium(the water column). Now we have a plant that is healthy and can grow at a maximum rate. If the NO3 levels varies between say 2-15ppm, then the various transporters will be degraded and more efficient transports(the HATs) specific to low N-NO3 levels will be put in their place. As a result, the plants growth rate will be reduced.
It takes more energy to concentrate nutrients when there is less in the external environment. So at higher levels, the plants use different transportors that take full advantage of the higher N-NO3 levels and grow faster as result.
Which is about what we find to be optimal for growth in the water column.
Seems the data was and has been there all along, just no one bothered to listen to Paul, nor look stuff up.
He looked at many lakes and plants and did a lot of tissue analysis beside this as well.
Reference:
Gerloff, G.C., and Krombholz, P.H., 1966. Tissue analysis as measure of nutrient availability for the growth of aquatic plants. Limnological Oceanography, 11:529-537. (Hutchinson, 351-357)
Regards,
Tom Barr
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