[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Algae:plant competition and carbon

Tom Barr wrote:

> I have been looking up some competing ideas for certain algae groups lately.
> Often you'll see something called the Redfield ratio in chemical
> oceanography. It'll have a ratio of something like Carbons: 106: Nitrogen:
> 16 and P: 1. This is also about the same ratio in phytoplankton.
> But looking at something such as Macrocystis, a larger brown kelp, you find
> this ratio is now 500 carbon to 15 N's and 1 P. So why is this? Why would it
> need more Carbon?
> It's larger and needs more support. The smaller phytoplanktons do not need
> this support like the larger beast, Macrocystis.

Tom and all,

I checked a couple sources and came up with (all in weight ratios):

C:N:P in aquatic plants (from Walstad, based on 40% carbon)
285:   11:1

Data from Raven:
C:N:P in phytoplankton
 75: 9-11:1  (Chlorella)
 49: 5- 9:1  (Euglena)

C:N:P in freshwater macroalgae
117: 6- 8:1  (Nitella)
174:   17:1  (Hydrodictyon)

C:N:P in marine macroalgae
106: 3- 4:1  (Macrocystis)
600:25-50:1  (Laminaria)

There's a huge variation in these values, and there was some data
processing involved but the trend is fairly clear.  Larger algaes have
more carbon relative to N and P than do smaller algaes.  Plants are
higher yet.  The Laminaria analysis is odd.  The P content is very low,
giving very high N:P and C:P values, but pretty normal C:N ratios.

In discussing variations among the algae, Raven suggested a correlation
between the high C content of the larger algaes to the presence of a
thicker cell wall.

Where are our typical nuisance algae relative to the types shown here? 
Green water is phytoplankton, so that's fairly clear.  Diatoms aren't
addressed.  My guess is that our tough, attached and filamentous algaes
have thick cells walls and are more similar to the macroalgaes than they
are to the phytoplankton.  Either way, carbon would still be higher in
plants than in algae.

Certainly it seems possible that carbon could limit plant growth in
cases where it doesn't limit algae growth.  On the other hand, there are
so many other variables involved that I don't think the compositional
analysis alone provides a very strong argument.

Interestingly (to me, anyway) Raven pointed out differences in the
concentration of electrolytes (K, Ca, Mg) between different algae and
related those to the volume of vacuoles in the cells.  It would be
interesting to see how that variation carried over into aquatic plants.

Roger Miller