[APD] RE: Acidity and nutrient uptake

["Steve Pushak" <teban at powersonic_bc.ca>]

Ed Hengel wrote:
> Does anyone have any information about Acidity and nutrient uptake.
> Specifically, does very low ph < 4.5 ( co2 ~ 25ppm, KH ~1) have an effect on
> plant/algae metabolism?

Most of the data which I have pertains to the effect of pH upon substrate activities. At low pH several reduction processes are
stimulated and so iron, phosphorus and manganese are generally more available at low pH (5.5-7). At lower pH phosphorus can be
complexed by iron and aluminum so at pH 4.5 you may have P shortage caused by aluminum fixation. There is a graph showing P
availability as a function of pH at <http://www.extension.umn.edu/distribution/cropsystems/DC0792.html> In the aquarium, the role of
aluminum phosphate fixation may be minor unless you have clay or fine mineral soil in your substrate.

Low pH is often associated with low levels of Ca and Mg; a shortage of calcium or magnesium is very serious for aquatic plants. pH
is a measure of hydrogen ion concentration so in itself it is not the cause of problems generally associated with soft water.

In the root zone, cation uptake is accomplished with the assistance of electrical attraction; positive hydrogen ions are released by
the plant creating a negative charge on the root which attracts positive ions. You can read more about these biochemical processes
by reading some of the material on my website specifically <http://home.infinet.net/teban/iron/ironw.html> This article focuses on
iron uptake and assimilation.

You may find Philip Barak's Soil Science web pages useful for a general understanding of nutrients and uptake mechanisms. See
<http://www.soils.wisc.edu/~barak/soilscience326/>

<http://courses.biology.utah.edu/bowling/5490/Class%20Handouts/L12,13%20Plant%20Nutrient%20Uptake%20Both%20Sets.pdf> is a good
introduction to plant nutrient concepts.

Interestingly, a low pH would inhibit ammonium uptake.

Are you trying to solve a particular problem or just interested in learning?

Steve P

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