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[APD] The "seed" theory with why algae does not grow when plants

Okay Tom, I'll bite... :)

I've argued these mechanisms for some time but I have still felt that algae
"know when to grow" and "when not to grow". I think it might make more
sense to folks to consider spores like plant seeds to understand and
consider this concept.

Tom, you are comparing the sophisticated biological function of a very advanced sexually reproducing plant to a primitive algae cell. I'm not sure I buy into the analogy... what scientific evidence exists for this triggering behavior? I have a copy of Endnote, and access to the major academic journals, please shoot me some references, I'm very interested in this :)

I'm not sure about some, some algae certainly sense NH4+, I've shown this
with Green water and staghorn, Urea can also be included there.

I do know of at least two people that use urea based nitrogen sources in their tank and do not have problems with either of these algaes.

I have been using a pelagic plant, Utricularia stellaris to investigate the
effect of well growing plant on the algae.

Deliberately using or accidently infected? :)

I think some of the key things they are already done has opened more
questions than answers. The paper tells me what is not the case(eg high
nutrients do not mean the lake will become algae covered and turbid), but
also has cases where the lake is pea soup with similar conditions. Both
states are stable.

Right, but we're making a huge mistake here comparing a lake to our tanks. Our tanks are artificial and despite all the 'hippie' like ramblings our tanks are not ecosystems and I am very suspect of drawing generalizations made about natural bodies of water and extending them to aquarium practice. The reef hobby was stuck for quite a while until they stopped trying to emulate natural water conditions and started meeting coral needs instead. I agree we need to give our plants what they need, but the mechanism keeping a lake algae free is unlikely to work in our little glass boxes. What is needed is well controlled experiments done on an aquarium scale.

Secondly, and a much more 'philosophical' point, natural systems are exposed to flow of energy and mass and for that reason tend to be highly complicated nonlinear systems (such as the weather). We must be very careful using "steady-state" (which is the proper term) to describe these systems, as this is not the same as equilibrium. Equilibrium is 1) a unique thermodynamic state and 2) stable to perturbations, whereas steady state simply means the process isn't changing with time. Steady states in complex dynamic systems can be very dependent on the precise path followed through time (what conditions existed in the lake years ago, spatial inhomogeneities) and unstable to perturbations (water changes 1C, add 0.1ppm NO3, etc... algae take over). But there are usually _multiple steady states_ in a non-linear system so even if you replicate the exact ending conditions there is no guarantee you'll reach the same end point... There may be an all algae as well as an all plant "solution" to given nutrient/environmental conditions. But there are even more interesting states the lake might be in, limit cycles oscillating from all plants to all algae but happening over a time frame too long for us to observe, especially if there is some essential nutrients that is very limited as has slow kinetics....

So perhaps it's NH4 cycling that occurs too fast to measure, but can be
traced using isotopes(which is what I'm doing now with a Sag).
But out of 319 lakes over  wide range, there's no pattern to suggest that
nutrients cause a lake to be full of plants and gin clear or pea soup with
Planted Aquariums might be able to isolate these issue better.

Tom, could you please publish some of this data you have/had in TAG? You mention experiments you have done in the past about GW, growth etc, Chlorophyll levels, etc... Some quantitative data with a good write up described the design of experiment would be helpful in evaluating the problem a little better and I think the interest level is here. You have access to some nice lab equipment and could really help us out... "The plural of anecdote is not data" :)

Jeff Ludwig
Elkton, MD

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