Leaky plants and leaky algae

[Thomas Barr <tcbiii at earthlink_net>]

Roger Miller has proposed some notions that plants leak organic chemicals
into the water column that can feed the algae(thanks for peaking my interest
here RM:) 

I looked at some algae and higher plant morphological differences. Algae do
not have a cuticle(in the algae that we deal with). What's this mean? It
means that algae simply has a cell wall and membrane to keep its contents
inside. Plants have a "skin", an epidermal layer. Some plants have a rather
thick layer(e.g. cactus), some thinner(e.g. Echinordorus berteroi).
Just on this notion alone, it would seem plausible that the plants have a
far superior set up for gaining an advantage in this area. Plants do
certainly leak things into the water. But algae appear to do this much more
so than plants do as far as a ratio based on biomass. Algae have less choice
in the matter also. Plants leak organics that may help(say allelopathic
chemicals) were as algae leak what it cannot hang on to(it just passes
through the membrane). Some species of algae leak alleopathic
chemicals(Cyano's). This is a large difference in how this "leakiness" plays
out.

This doesn't not appear to be a predominant mechanism where large frequent
water changes are preformed but in non CO2 tanks it would seem to play a
larger role. As temperature rises algae also leak more. I'm trying to find
some literature that says the same for the plants. A stressed plant often
leaks more than a healthy plant. But do they produce more organics as a
result in temperature increase or more a result of a stress inducement? At
some point the heat will cause stress and enzymes to denature but below that
level there might be something else going on.

I believe that a healthy plant will not leak very much if at all in some
cases and what has been shown to be leakiness, is more a sign of a stress
inducement(like say not enough N, so the plant produces a chemical(s) that
frees up N somehow). Plants will leak chemicals, but only ones that are
waste, allelopathic or for some unknown reason.

So do these leaked organics help or hinder aquatic plants themselves? Does
it matter if the organics came from the plants or the algae? Will algae do
better with leaked organics(from plant or algae)?

I would argue that the answer is no IF the nutrients supply is in good
shape. The algae and the plants both would not benefit from this "leakyness"
at all. They only gain an advantage at low nutrient levels when nutrients
become scarce. Same goes for the root article in FRESHWATER BIOLOGY
journal(Feb 2002). 

Regards, 
Tom Barr