Nitrogen uptake kinetics


Junior Poster
Apr 14, 2006
Karlstad, Sweden
Size-dependent nitrogen uptake in micro- and macroalgae
Hein, M; Foldager Pedersen, M; Sand-Jensen, K
Marine ecology progress series. Vol. 118, no. 1-3, pp. 247-253.


The role of algal size as a controlling factor for nitrogen uptake kinetics is examined by comparing published values of N uptake rate and half-saturation constants in micro- and macroalgae. The uptake kinetics differ substantially among algae very different in size. Microalgae take up nitrogen much faster per unit of biomass than macroalgae at both high and low substrate concentrations, and microalgae have significantly higher affinity for nitrogen than macroalgae. These typical differences in the uptake kinetics among small and large algae are commonly attributed to size-specific differences in the relative surface area (SA:V). Regression analysis demonstrates that size-specific variations in the kinetic parameters can be attributed to changes in relative surface area over an extensive range of algal sizes, covering both micro- and macroalgae. These results agree with previously described relationships between maximum uptake rate of nutrients (nitrogen and phosphorus) and SA:V within narrow size-ranges (either phytoplankton or macroalgae), and emphasize the existence of a general coupling between physiological and morphological properties in algae.


Can this be interpreted as the reason why macros outcompete microalgae when nutrients are unlimited? And under limitation the higher uptake ratio rewards the microalgae a larger portion of transient nutrients?

Tom Barr

Staff member
Jan 23, 2005

I made this point back in 1999-2000 on the APD, such evidence falls on deaf ears in the hobby as a rule. All marine and freshwater phycologist already know this.
Basic stuff that's taught to aquatic biologist.

Sans Jensen is a good researcher in Europe.

When I talk about the algae not being in the same ecological niche, it's that 1/2 constants, the nutrient demand differences and so forth, but some fool will demand me to prove it further, bitch and whine.

Show them some Master's level research project, spending 2-3 years on it and cover every possible base.............all while they don't do jack and are too damn lazy to look up a single reference themselves.

These same folks also have basic troubles with algae, virtually no control over their problems but are extremely verbose when it comes to posting their lack of knowledge on the matter.

What would be interesting, but seldom done, is the kinetic differences between NH4 and NO3 of these groups.

I often use the mouse and elephant as an example, the mouse clearly is quick and can nab small amounts of plant material, whereas the much larger elephant requires larger amounts of food.

Also, they did not discuss the life histories of the macro vs the micro algae, or perhaps in the discussion or intro they did address it, but like elephants and mice, one breeds like flies sexually, the other is very slow.

Same deal with algae and our plants, the plants we only have vegetative methods as a rule, the algae are all sexual in our tanks, this affords them many resistant resting stages till things go sour again.

I'm not sure why so many think they out compete eachother, because they are not even in the same niche.

For competition to occur, you need to have competition for resources.
Algae and plants are not limited by resources in our tanks though...........
When we stop adding enough CO2, nutrients etc, then the micro algae attack.

The form of the Nitrogen would also make a difference, relative to a single cell/spore, the NH4 represents a much larger energy bonus and a good signle that all the best form of N is available and ready to be utilized by the spores.

NO3 is not nearly as desirable to a spore and oftern will not tell you if the nutrients are good enough to grow and make it through a life cycle.

NH4 to a large billion celled plant while having less energy demand for its usage, represents a much smaller gain for the plant vs the single celled algae spore.
So there's less difference using NH4 vs NO3 in plant culture vs algae.

Once the algae has committed to germination, it must be aggressive and finish it's life cycle. So it'll use whatever is around, NO3 or NH4, whatever it takes to make a go of it.

Tom Barr


Prolific Poster
Jun 4, 2006
Every answer from You, Tom, is a true relief, especially your comment on all those lazy whiners!! Very educative, but also very funny, hahaha, You nailed it, Tom! :D
I am not sure why folks are so concervative and believe more in the myths then in the knowledge... Probably because ppl have trouble in distinguishing myths from knowledge or something.

The thing that beats me is that oftentime ppl even get kind of semiagressive when one introduces some ideas that goes against all they stand for. For example the simple fact that nitrogen doesn't cause pestalgae in marine enviroment... or that its pretty easy to trigger greenwater with too much phosphate in saltwater (I managed to overdose it, hehe). Even such harmless statements are not well met and should be proved way way way beyond reasonable doubt, haha, and even then ppl doubt and whine... Anyways, good answer, Tom, I feel Your "pain", and thank you Morphriz, my geeky friend! :)

Tom Barr

Staff member
Jan 23, 2005
But basic stuff will still elude those who are too lazy to even be bothered with looking anything up, but still want to insist they are the "voice of reason" and the authority.

Everything is speculation to some degree, law, science, critical thinking etc.
There is no total absolution.

Where you make that reasonable cut off is important, some never get that point.

Later, I might hope that they will, they might change after all.

I base my notions on what seems most reasonable given what we know and observe. We wonder through the observations, try out hypothesis to explain stuff. Then we test, then we try and make some sense out of things.

I honestly am not going to bother doing a well funded research project level thesis everytime I do some test to see if PO4 causes algae or not in the hobby.

I already know in practical terms it does not.
So do other folks that try it and focus in on the parameters.
Instead, I see what is most reasonable with the amount of $ and time I do have. That's all I have to offer.

Even with the limitations there, I've manged to get much farther than most.

But I still get these fools that seem to insist that I be held to that level of rigor when they cannot even help a person with algae nor have enough control over their own systems at home etc, to even do a decent experiment that rules out all the issues they are bitching about.
If they actually did the experiments and try them out, rather than merely trying to win some on line web argument, they would know a lot more and realize these limitations.

But it's about ego, not information and learning.

The good thing about the approaches I try is that they are universal, they apply to CO2 enriched and non CO2 systems as well and address sediment and water column related issues.

Simply using an algae inducement model to determine likely causation for blooms has eluded aquarist, but it a very powerful simple tool to address such noxious over discussed issues.

You'd figure someone would do more on this topic given all the hassle, all effort in attempts at resolving the issue, labor etc.

That's how I went about it anyway.

Works too, better than the other speculators and snake oil vendors.
So right there, (even if I am wrong, which I might be), I'm still a lot closer to being right than these clowns.

I also never seem to get any supporting references from these folks also oddly, no test methods and possible issues one might look for that confound the results potentially .........why is that? :cool:

It's easy to be a hack, give folks a hard time personally, but it's much harder and much more a positive influence on the hobby to take the other path.

Tom Barr