algae CO2 compensation points

Just a FYI about algae, freshwater algae, not some esoteric Redfield ratio about marine phytoplankton................and the amount of CO2 they require.....

Measurement of Carbon Dioxide Compensation Points of Freshwater Algae -- Birmingham and Colman 64 (5): 892 -- PLANT PHYSIOLOGY

We can see they are hardly limited by CO2, they also are very very small and their total biomass is also very small relative to most any planted tank, so they have far fewer needs for carbon than say a large plant with lots of structure(which requires a lot more Carbon).

Regards,
Tom Barr

 

Yes, this is why we cannot limit algae.
Think about how N, P etc relate to the ratio of carbon use.

Say the carbon is the same as the Redfield ratio, or even less, say 1/2 that for FW.
106/2 = 53 Carbon atoms for 16 N and 1 P atom.

Removing the O2/O3 etc
0.01 ppm C ~ 0.003N or 3 parts per billion and now let's go to P. => 0.00019 ppm P, which is over 2 orders of magnitude lower than any test kit sold for P.

Sub parts per Billion ranges...............fish likely leak more P than is required.............so do plant tissues..........

If you use RR that is.........I think FW algae are more in the range of 14: for N.
Carbon is about the same though, still, it's just an average.

But if you use 106 C, then these numbers drop even farther and support the idea that limiting the algae is very difficult unless you are in open oceans, large lakes, have lots of light, lots of algae and time. Then, they can and do become limited.

So what happens when plants are provided with stable CO2 which is their largest enzymatic and energy input(making sugars from carbon is what they do and what they are all about), and N, P etc?

They grow well.

Even in non CO2 planted aquariums, algae are still not CO2 limited.
Nor are they nutrient limited.

What is left? Light.............disturbances, limiting plants..........changes in concentrations(but not limitations) that may signal a good time for germination.

Etc.

I've long argued this is not about limiting algae.
If you look at CO2 and other nutrients and algae growth, then use ratios like the Redfield of a FW version, then you can predict how much N and P are required, or Fe, to limit algae.

In deep northern lakes, adding P in the summer should increase algae as these are deep, good sized systems, lacking plants, lots of light over long days(Northern summers), and the P enrichment studies and rational for P limiting systems comes from such systems. At the lake edge, the algae are not limited, however, most of the open water, far from sources of P and lots of other algae under high light and long days will grow like mad.

If you go to Florida with shallow lakes, moderate light routines(still quite high intensity though if not more), lots of plants, this is not as common. In fact, there's no evidence of this eutrophication and we find a very high correlation between 30-50% plant infested lakes and clear water.

While this is not a direct way at figuring out how much P is required to limit algae, it does show an expected/predicted/modeled range.

Regards,
Tom Barr