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Re: [APD] Iron, physidophores and UV

Okay, one thing no one seems to realize and discuss is that the intensity of the sun's UV's are very high. It is also "always on" during a large portion of the day hitting most of the water.


Compare this amount of UV energy to a UV sterilizer that has water pass through it for 1-2 seconds perhaps 2-10x per hour.


The other issue that the UV's wavelength is different than the Sun's and generally more narrow. Many chemical bonds and complexs are specific to a particular wavelength for degradation. 

Given that people have only actually used field data from natural systems to justify the UV sterilizer claims that it breaks down iron complexes, RATHER than any real data from an aquarium, this seems speculative at best and at worst simply wrong/insignificant. 


I think the burden should be on those wanting to make this claim to show that it is or is not significant.


The observations with using UV's and dosing traces sure don't seem to support their contention.


I've given several good reasons why.

>The method by which plants 
>extract iron from EDTA is when the EDTA-iron is pulled down into the 
>root zone where the pH is much lower and thus conditions are 
>conducive to extraction of iron by the plants directly as it is 
>released from the chelate under the acid conditions or the plants can 
>also utilize phytosiderophores to extract the iron directly. However, 
>in the water column there is no release of iron (-> insert shameless 
>pitch here - use Flourish Iron to target leaves, stems as well as 
>root zone - it is non-EDTA based).

*Some plants*, only grasses, (unless you have research suggesting otherwise), utilize phytosiderophores to extract the iron.. People hear  phytosiderophores and automatically assume __all__ plants do this. That is not true.


www.rosier-be.com/media/Rosafit en.pdf





EDTA ___is applied as a foliar__(thus leaf uptake does occur in a wide variety of plants) micro nutrient. 


DPTH is a better chelator as opposed to EDTA since the pH is more useful for our application.......EDTA is useful up to about a pH of 6.3 whereas DPTH is good for up to a pH of 7.5.


 So plants most certainly can and do take in Fe EDTA via their leaves in many agriculatural crops, it is very unlikely that aquatic plants would be any different.



How do algae obtain Fe? They have no roots and their descendants are root bearing plants, why would they lose the foliar uptake ability? What about Riccia? Moss? Java fern and other plants without sediment bearing roots?


This not does fit well with aquatic plant observations nor with research on foliar applications.

Gentner 1976: Uptake and transport of iron and phosphate by Vallisneria spiralis L. 

It appears that aquatic plants do take in Fe from the leaves in the form of EDTA. 


Haller et al 1976 also used Fe EDTA with Hydrilla and found growth rates increase when they had relatively high(very high considering PMDD's standards of a wimpy 0.1ppm range) of 6.0 to 8.0ppm Fe. This was primarily from foliar uptake. 

> U.V. light would break down the compound (& chelated nutrients)
>>rapidly and thus exhaust it quickly.

>This would make sense, the chelate would rapidly release the iron which would then rapidly >fall out as iron oxide, thus rapidly removing all of it from the water column so it could no >longer resupply the root zone with this iron source. Eventually the precipitate would work into >the root zone but it would take awhile.
>Greg Morin


That assumes plants can only use Fe in the roots from EDTA and other forms of Fe, but this is not true, see above. Observational experience is counter to this and plants will use some of the Fe prior to it being oxidized. 

But the other argument is that the iron would be available for a longer time frame than say a less strongly bound chelator complex. So over time, the iron would be available longer to the plants even if the energy required was a little more to remove the iron from the complex.


This presents a good arguement also. 


That's fine if you dose frequently or have low iron demand, but here's an idea for you :

Use both the gluconate form and the DTPH form.

Then you get the benefits of both.


But is the amount energy significant in the various Fe chelator/complex forms to the overall status of the plant of one versus another form? Fe is a trace after all, not much is needed. So is the form of Fe really going to make a difference?


I think having some available whether dosed through DPTH or more frequently from weaker complexs works fine. You can dose pulses also and still maintain non deficent Iron levels as well as using low light tanks to and rely on the sediment almost exclusively. 



Tom Barr 



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