compensation point

To: Aquatic-Plants at actwin_com
Subject: compensation point
From: "Robb D. VanPutte" <ROBB at bio_tamu.edu>
Date: Mon, 25 Mar 1996 9:26:21 -0600

John Shane wrote:

I have a distant memory from school biology of a concept known as "The
Compensation Point". This (if I remember correctly) is a state that terrestial
plants strive to achieve where the O2 + sugars produced by photosynthesis
are entirely used up in respiration and the water + CO2 produced by respiration
are entirely used up in photosynthesis. The plant is in an optimum state of
equillibrium and is evolved to reach this point for its given growing
conditions.

This definition of compensation point is a little confusing. Usually it is expressed as a net
rate of oxygen evolution equal to zero. In other words, the rate at which the plant is
evolving oxygen due to photosynthesis is equal to the rate at which the plant is using
oxygen in aerobic respiration. Any plant that is at its compensation point is not producing
extra photosynthate (sugars) which it can store and utilize during the nighttime for
respiration. Consequently, this state of equilibruim is detrimental to the health of a plant.
Ideally, the plant needs to be photosynthesizing at a rate much greater then its respiration
rate so that extra energy (in the form of sugars) will be produced that can be used for
growth and reproduction. I don't know much about higher plant physiology (I've been
trained as an algal physiologist) but I can't believe that a plant would strive for this
equilibruim all of the time.

Therefore, I would say that this is not the condition we should be striving for with our
aquarium plants. We want them to grow and flourish in the aquarium. I hope this clears up
the issue.
Robb D. VanPutte
Dept. of Biology
Texas A&M University