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What Is Optimal Growth?


  1. Terminology, Nutrition
    by eworobe/cc.UManitoba.CA (Sun, 25 Oct 1998)
  2. Sv: Aquatic Plants Digest V3 #724/light and co2
    by "Ole Larsen" <bse9195/> (Tue, 5 Jan 1999)

Terminology, Nutrition

by eworobe/cc.UManitoba.CA
Date: Sun, 25 Oct 1998

Growth is a technical term which refers to the rate at which plants 
increase their biomass. It is generally reported as grams produced per 
gram extant per day. A constant growth rate will therefore produce an 
exponential increase in biomass over time. An optimal or maximal growth 
rate is the maximum intrinsic growth rate of a given plant. Generally, 
for fast growing submerged plants this is a doubling time of 1 to 4 days. 
This means that if your tank is 1/4 full of plants it will be completely 
full in 2 to 8 days. If you then remove 3/4 of those plants, your tank 
will again be completely full in another 2 to 8 days... and so on.

With this as a benchmark, it is clear that NO ONE on this list has plants 
which exhibit 'good growth'. What successful aquarists have are stable 
tanks with a high 'standing crop' of healthy populations of plants. Of 
course, few would want to have to deal with optimal growth rates!

Optimal growth rates require at least 20% full sunlight (400 umol/m2/sec 
PAR or 2 klux), moderate to rapid water movement, about 20 ppm CO2 in an 
acidic or neutral tank or a pH of around 8 to 8.5 (which will deliver 
about 45 ppm CO2 as bicarbonate), an adequate replacement rate for 
mineral nutrients (either through fertilization or a flow through 
There is no way that infertile clay substrates can support optimal growth 
rates. This has been proven many times over the past 100 years using a 
wide variety of substrates and a wide variety of aquatic plants.

Having said that, the use of laterite (which is a highly weathered clay SOIL
found in hot, humid climates that contains large amounts of iron and 
aluminum hydroxide and little organic matter) is an effective and SAFE 
way to produce stable tanks with healthy plants and a high 'standing crop'.

If you want to be SAFE, then use a laterite soil. Dont fool yourself into 
thinking that your growth rates will be high. If you like to experiment, 
then get a shovel and find your own mix... you may experience disaster, 
and you may find that your plants have taken over your room during the day.


There is generally a threshold concentration below which nutrient uptake 
will be reduced and be insufficient for the needs of the plant. You need 
a concentration in the tank for a given nutrient that will supply the 
plants requirements without falling over time. For Calcium there is also 
a water column requirement apart from that amount needed within the 
plant. This is because Ca is crucial in maintaining membrane integrity 
and cell wall structure, both of which are apoplastic (outside the cell 
membrane) processes. 


Sv: Aquatic Plants Digest V3 #724/light and co2

by "Ole Larsen" <bse9195/>
Date: Tue, 5 Jan 1999

Hello all.

In Digest 724 I posted a message ( question) on the interaction of light and CO2 remembered from a lecture nov. 1997 at Aqua Planta Scandinavica by prof. Ole Pedersen, F. W. Lab., Univ. of Copenhagen.
Later I promised to come back when/if I got response to my e-mail from O.P.
Now I have it in photocopy.

It is from +ACI-Plant, Cell and Environment (1994) 17, 955-962+ACI-

+ACI-The interactive effects of light and inorganic carbon on aquatic plant growth+ACI- by
T.V.Madsen (Dept. of Plant Ecolo., Aarhus Univ.) and K. Sand-Jensen (FW Biol. lab. Univ. of Copenhagen).

It is 8 A-4+ALQ-s so I+ALQ-ll just give a little of the discussion. Those who consider this important will know how to get
a copy of the complete article.

+ACI- Our results established co-limitation of aquatic plant growth by light and inorganic carbon and demonstrate marked growth enhancement by inorganic carbon at low as well as at hight  light................but the pronounced
growth enhancement by elevated inorganic carbon at low light and the increase in light-use effiency for
growth are new observations that illustrate the insuffiency of Liebig+ALQ-s minimum theory (Liebig 1870)
which is so widely used in aquatic plant ecology.....................The positive effect suggested can result from the 
suppression of the oxygenase activity of Rubisco by increased internal inorganic carbon concentrations.................The savings in terms of NADPH and ATP, 
which are otherwise used in  photorespiratory carbon oxidation, can then be allocated to 
photosyntetic  carbon assimilation, resulting in improved  light-use effiency+ACI-
The plants were Eleodea canadensis L.C. Rich and Callictrice cophocarpa Sendtner

This certainly answered my original question (724)
Hope it  interested a few of you
Ole Larsen

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