# What drives uptake rate?



## banderbe (Nov 17, 2005)

Perhaps this is a dumb question.. but I wonder what drives the nutrient uptake rate of plants.

Obviously the amount of light is the primary factor in how rapidly the plant photosynthesizes.

But, does the amount of nutrients (assuming none are zero) impact the nutrient uptake rate?

What about the amount of CO2 (again assuming it's not at zero)?

In other words assume we have a tank that is at 4 WPG.

First scenario, the CO2 is 15 ppm, NO3 is < 10 ppm, PO4 is ~0.1 ppm. In other words this tank's nutrient regime is "lean".

Second scenario, the CO2 is 45 ppm, NO3 is ~30 ppm, PO4 is ~3 ppm. These are values one might expect to see in a tank using standard EI dosing regime.

Will nutrients be used slower (and consequently plants will grow slower) in a "lean" tank? Will plants grow faster in the tank with more generous amounts of nutrients? Again, assuming lighting is a constant in both scenarios and that nothing is "limiting". (My understanding of "limiting" is that a nutrient macro or micro actually runs out - correct me if I am wrong).

I ask because I have seen a few folks asserting that in order to keep their plants from growing too quickly they use a "lean" dosing regime but it seems to me that the plants would use nutrients at a constant rate regardless of the quantity of nutrients in solution.

Thanks for any feedback!


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## yildirim (Nov 25, 2004)

My current tank is a third scenario which doubles everything in your second. I tried first in the past for a long time but second obviously resulted an incredible growth rate and less algea. Plants will not stay the same size, will grow continuously and require more nutrients everytime.


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## plantbrain (Jan 23, 2004)

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## banderbe (Nov 17, 2005)

plantbrain said:


> As 4w/gal is not a standard level in the terms of the plant, depends on how high the light is, how long it's on, bulb age, aquascape, pruning/selfshading issue.
> 
> Plant species variability, different plants will take up more/less.
> 
> ...


Yeah my scenario assumes the same light, same bioload, same plants, same everything. Given only variation in the levels of CO2 and/or nutrients.. does more cause faster growth. If so, why?



> So.....leaner tanks, particularly PO4 limited ones can slow down the rest if the growth without as much damage to growth but the trade off is often times some GSA.


Tom, by PO4 limited do you mean that PO4 has gone to 0 ppm?



> Upkeep and maintaining a good nutrients balance without falling off and limiting something seriously is a user issue.
> 
> Slight limitations and consistent relief from frequent dosing can help.
> Plants regulate their needs and plants also take up more nutrients than they need.


I understand what you mean about plants taking more than they need, but does the mere existance of more nutrients *cause* them to take more at a higher rate? Sounds like the answer is no.



> We eat more than the bare minmum of food required for health and growth don't we?
> 
> Many folks that try the leaner methods general had lots of troubles in the past. The problem is worst these days not because of nutrients/dosign more etc, it's because folks do add 4-6 w/PC lighting.
> 
> That's a harder balance to achieve, so if you want slower growth, try less light, these plants are all generally low light plants.


Okay so it sounds like we agree, the amount of nutrients in solution (assuming none are limiting) will not cause plants to grow faster or slower. It's riskier to run a tank lean but a strategy to slow plant growth by keeping nutrient concentrations low (again, not limiting) is not going to result in slow plant growth.



> Less l;ight= slower growth, that also applies to algae, slower algae growth.
> 
> Leaner tanks are easier to balance, as well as EI tanks.
> 
> ...


Alright, well it sounds like based on what you've said that assuming no nutrient is limiting, the actual concentration of nutrients in solution (e.g. 5 ppm NO3 vs 30 ppm NO3) will not have any impact on the rate of plant growth / nutrient uptake rates.

It's riskier to run a tank lean, but that's another issue 

It seems to me that even if NO3 were at 1 ppm _consistantly_, that is 1 ppm above what the plants are taking out of the water, is that correct?


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## Laith (Sep 4, 2004)

Interesting thread...

I've always found that plants like the following, and in this order:

Light, carbon (eg CO2), macros and then micros.

If you have high light, low carbon then dosing lots of macros and micros will not drive uptake and plant growth.

If you have high light, good carbon and no macros, dosing lots of micros will not drive uptake and plant growth.

If you have low light (eg <1wpg), adding CO2 will still help a little but adding lots of macros and micros will not change anything.

And, interestingly, if you have good light, good CO2, only partially good macros (NO3 but no PO4 for example) and good micros, the plants will have a lower uptake of NO3 and the micros than when PO4 is present. Which is why sometimes when people start adding adequate amounts of PO4, they think that the PO4 is causing algae when actually the addition of PO4 has caused a deficiency of something else (NO3 through better uptake)...

Just my two cents


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## Ransom (May 3, 2006)

It seems that the level/concentration would have some effect otherwise you could just running airstones would keep your tank at 3% CO2 all the time and that would be just as good as having 30% injected all the time. 

Therefore, I am (totally) guessing that it must be easier for the plants to extract chemicals from the water if the concentration is higher - i.e. whatever mechanism that the plant uses to absorb one iron molecule per period of time has a better chance of succeeding if there are 500 iron molecules floating by in that time than if there is only one.


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## Edward (May 25, 2004)

There is no visible difference in growth at equal light and CO2, regardless the other nutrient levels. As long as nothing is limited plants are growing well. 

Some suggest more and more is better. Well, then try it. Make 300 ppm NO3, 30 ppm PO4, 20 ppm Fe, 100 ppm Mg and 400 ppm Ca. Give it 4 weeks and then post pictures. Any volunteer?


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## plantbrain (Jan 23, 2004)

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## plantbrain (Jan 23, 2004)

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## plantbrain (Jan 23, 2004)

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## bleaklow (Jan 12, 2006)

Tom would you say that Amano's tanks (thinking of some of the setups in the aquarium world books) fall into the lean (but balanced) regime? I'd always noticed that that his WPG values are never particularly high?


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## banderbe (Nov 17, 2005)

bleaklow said:


> Tom would you say that Amano's tanks (thinking of some of the setups in the aquarium world books) fall into the lean (but balanced) regime? I'd always noticed that that his WPG values are never particularly high?


His WPG values seem pretty high to me. 5 WPG or more in most of the tanks in NAW Vol. 1.


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## Laith (Sep 4, 2004)

banderbe said:


> His WPG values seem pretty high to me. 5 WPG or more in most of the tanks in NAW Vol. 1.


But usually not for the full photoperiod, only a noon burst. Or was he not doing this back then?


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## banderbe (Nov 17, 2005)

Laith said:


> But usually not for the full photoperiod, only a noon burst. Or was he not doing this back then?


Not sure, the first book doesn't mention anything about noon-bursts.


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## plantbrain (Jan 23, 2004)

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