This was a good study, I think folks read into the notion of preferences etc, while it did show when and how much PO4 was taken in, it does not show what different fertilizing routines would do to total dry weight biomass.

But it is clear that PO4 is taken in via the leaves during the day.
Not the roots as many like to claim and generalize and this is a true aqutic, the authors also references previous recent work by Cedergreen and confirms what they found as well regarding leaf uptake of nutrients.

http://www.int-res.com/articles/ab2008/3/b003p209.pdf

We need to be careful though, some think that adding PO4 only during the light is wisest, given a choice, simply having enough during the entire time, light or dark is the best. PO4 can hang around till the morning and you will not end up getting any more growth whether you dose at night or the morning.

Regards,
Tom Barr

When we prune our plants we are removing the phosphates that the plants used. So, PO4 leakage isn't going to be a problem in any case in an aquarium, even though it might be in a lake where mature plants are not removed.

Very interesting paper, even though I didn't read the whole thing. I like having a data point where the phosphate absorption of the foliage is found to be 5X that of the roots. To me that reinforces the fact that water column fertilizing is at least as effective as substrate fertilizing, for this plant if not for others.

Well, the thing is the species of plant is very important here.
Also, the methods used.

Split chamber methods are fairly noted, we do this same type of thing here with herbicide translocation and C14. Still, it's counter to most references and claims that aquatic plants uptake PO4 and prefer it from the roots.

This is a true aquatic plant as well.
Cedergreen and Madsen (2001-2002)also found similar results in dry weights and root formation under similar conditions for P, and N.

So it really shows strong evidence that water column fertilizers, at least with some of the easier to grow faster growing species, is the preferred method of uptake, not roots.

This is counter to research done by Barko and Smart which is heavily cited.
I think given the quality of this paper and that of Cedergreen and Madsen, and the species specific focus here, I have more questions about which species are and are not "preferring" something.

I've grown sword plants very very very, okay, too well for my own good, without any sediment nutrients.

Same with Crypts.

I read these claims all the time though.
Big roots are simply storage organs, runner daughter plants, mechanical anchoring in streams/rivers where they come from and to access nutrients/water when the dry season occurs and the water level drops.

Elodea, pondweeds, Egeria, Hornwort etc are true aquatics, they live all their lives under water or as seeds, tubers, turions or perhaps a few floating leaves here and there.

Regards,
Tom Barr

Here's Cedergreen and Madsen's paper:

Wiley InterScience :: Session Cookies

and older paper by Westlake about current effects:

Some Effects of Low-velocity Currents on the Metabolism of Aquatic Macrophytes -- WESTLAKE 18 (2): 187 -- Journal of Experimental Botany

Regards,
tom Barr

Here's an article that claims the opposite:

http://www.sciencemag.org/cgi/conten...t/207/4434/987

However, I know the methods used, the 2008 paper is very well done and cannot be denied. What is not yet clear to me as of yet, is why and how these authors came to such different conclusions. Cedergreen and Madsen also did an simple but elegant example that showed no differences in growth rates as long as the nutrients where supplied somewhere.

I know based on my own as well as many other aquatic plant hobbyists that Cedergreen and Madsen as well as the new paper would seem more likely correct based on our observations in aquariums.

Using P33 studies is a lot nicer than the nasty P32 radioactive stuff, that's a PITA.

Regards,
Tom Barr

Hi Tom,
What I found significantly different about the Cedergreen experiment is that the shoot portion was exposed to open water whereas the Angelstein/Schubert Experiments with E. nuttallii used controlled water in both root and shoot locations starving one while feeding the other. I don't see where Cedergreen measured the P content of the open water other than to say that the waters were eutrophic. It also does not appear that he took into account the effects of flow as discussed in the Westlake report.

Could it be that Cedergreen's results were due to a relatively higher effective concentration of sediment to water column P while Angelstein/Schubert simply shows that the leaf has a higher uptake rate capacity if given the chance?

In his concluding paragraph Cedergreen himself states: "...Only in rarely encountered hypereutrophic waters is there significant P uptake from the water. Therefore, the relative contribution of water and sediments appears to be a function of their relative P availability..."

Cheers,

Oh, really!?


WRONG.
Don't bee fooled with this baloney. See here...

I have tried water column fertilizing with an inert substrate with on three occasions. None came close to achieving the growth that I get with a soil substrate.

This is in non-injected, lower light environments.

Sometimes soil-based environments require water column dosing. I think Tom said that substrate and water column fertilizing provide the best both of approaches.

Bill

More times than I can count over the years.
ADA adds and suggest water column ferts as well

Enough said.

I have different goals and concepts about why I do this, but like you, you might have differing goals that are not those of ADA or Naman's.

I help folks achieve a goal, no matter what it is, with aquatic plants.
Some know they neglect, some want fast growth rates, some want to know why algae is blooming, some want to know if the water column is an effective method for dosing PO4(alone or in conjunction with sediment sources).

I've offered for some years now why both is best as far as method, not this "either or" business.

Of course I have few algae issues as does Amano.
So perhaps it's not the water column that's the issue with algae after all:idea:


Regards,
Tom Barr