[APD] sand cap for nutrients & amino acid uptake by roots

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

Scott R.H. asks:
> Would it be possible to make a layered substrate with
> "cap" of sand/light clay mix.  Or just fine sand.
> ...  This way you can lock your macros
> away for when the roots delve deeper.

A layer of sand is very porous in comparison to clay. You would have
dissolved nutrients leaching out into the aquarium water.

The problem with putting fertilizer in a layer underneath a clay cap are as
follows:

a) Delayed access: the clay cap needs to be thick enough & it will take
considerable time for roots to grow through it to access the nutrients
there. Chemotrophism will not direct root growth because diffusion will be
too slow.

b) Denitrification, sulphate reduction: a permeable layer under the clay
would permit a lot of mixing there & bacteria will have an opportunity to
act upon the nitrates to produce nitrogen gas (denitrification). If there
are sulfur compounds, you will get very low redox & production of sulphides.
Since the layer is porous, plant roots would not be able to sufficiently
oxidise a local region around the root hairs for protection; they would not
penetrate beyond the protection of the clay layer. See my comments in the
Krib at <http://www.thekrib.com/Plants/Fertilizer/roots.html#2>. Dr Dave &
Charley Bay also have very interesting comments in this same collection of
postings.

c) Leakage: inevitably you will make a hole in the clay through which
nutrients & toxic by-products will leach out. This would happen if you
uprooted a plant with a tap root or inserted a digging instrument to chop
through roots for plant removal.

d) Low iron availability: many clays contain high amounts of calcium, and
increase pH thereby limiting Fe availability.

If on the other hand, you put ammonium nitrate (or other N fertilizer)
inside a small clay ball, you can place it very close to the target roots so
root hair penetration can occur within a few weeks.

If there is no organic material or carbon inside the clay ball,
denitrification cannot occur there.

Root hairs can release oxygen when they penetrate a micro-region containing
ammonia; this will oxidize the ammonia to nitrite or nitrate & will protect
the root from the toxic effects of the ammonia. Some ammonia can be taken up
directly by the root hairs provided that the concentration is not too high.

I believe that soluble phosphate salts (such as N-P-K fertilizer) can also
be embedded within clay balls. Mineral phosphates (as in rocks or bone meal)
on the other hand would probably require the presence of organic material to
facilitate solubilization. You don't have to be concerned about the loss of
phosphorus in a substrate as you do for nitrogen; it stays in the substrate
& is easily accessed by plant roots there. I have not researched phosphorus
availability in substrates as much as nitrogen.

See <http://www.soils.umn.edu/academics/classes/soil3416/lecture3.htm> for a
discussion of nutrient uptake in soils. See
<http://www.wetlands.com/coe/87manapc.htm> for a summary of morphological &
physiological adaptations to anaerobic root conditions.
<http://www.agron.iastate.edu/courses/agron230/notes/nutrient.htm> is a good
summary of nutrient uptake, transport & assimilation.

I did find several references which indicates dissolved organic nitrogen
(amino acids) exist within soils & are taken up by plant roots.
See <http://geode.colorado.edu/~jneff/Publications/NeffFrontiers2003.pdf>
<http://jxb.oupjournals.org/cgi/content/full/53/379/2305>
<http://www.utsc.utoronto.ca/~britto/publications/minra.pdf>
<http://mycorrhiza.ag.utk.edu/latest/latest02/02_10yu1.htm>

The Neff article is probably the best of the above.

Below are other references if you have access to a research library.

Henry HAL, Jefferies RL. 2002. Free amino acid, ammonium and nitrate
concentrations in soil solutions of a grazed coastal marsh in relation to
plant growth. Plant, Cell and Environment 25, 665-676.

Kielland K. 1994. Amino acid absorption by arctic plants: implications for
plant nutrition and nitrogen cycling. Ecology 75, 2373-2383.

Nasholm T, Ekblad A, Nordin A, Giesler R, Hogberg M, Hogberg P. 1998. Boreal
forest plants take up organic nitrogen. Nature 392, 914-916.

Nasholm T, Huss-Danell K, Hogberg P. 2000. Uptake of organic nitrogen in the
field by four agriculturally important plant species. Ecology 81, 1155-1161.

Nasholm T, Huss-Danell K, Hogberg P. 2001. Uptake of glycine by field-grown
wheat. New Phytologist 150, 59-63.

Nasholm T, Persson J. 2001. Plant acquisition of organic nitrogen in boreal
forests. Physiologia Plantarum 111, 419-426.

Raab TK, Lipson DA, Monson RK. 1999. Soil amino acid utilization among
species of the Cyperaceae: Plant and soil processes. Ecology 80, 2408-2419.

Sarojini G, Oliver DJ. 1985. Inhibition of glycine oxidation by
carboxymethoxylamine, methoxylamine and acethydrazide. Plant Physiology 77,
786-789.

Schiller P, Heilmeier H, Hartung W. 1998b. Uptake of amino acids by the
aquatic resurrection plant Chamaegigas intrepidus and its implication for
N-nutrition. Oecologia 117, 63-69.

Schmidt S, Stewart GR. 1999. Glycine metabolism by plant roots and its
occurrence in Australian plant communities. Australian Journal of Plant
Physiology 26, 253-264.

Streeter TC, Bol R, Bardgett RD. 2000. Amino acids as a nitrogen source in
temperate upland grasslands: the use of dual labelled (13C, 15N)glycine to
test for direct uptake by dominant grasses. Rapid Communications in Mass
Spectrometry 14, 1351-1355.[Medline]

Thornton B. 2001. Uptake of glycine by non-mycorrhizal Lolium perenne.
Journal of Experimental Botany 52, 1315-1322.
<http://jxb.oupjournals.org/cgi/content/abstract/52/359/1315?ijkey=0252d0c99
cd07ad2e1951eb400f7c78f6429ac45&keytype2=tf_ipsecsha>

Steve P in rainy Vancouver, no more snow! :-(

_______________________________________________
Aquatic-Plants mailing list
Aquatic-Plants at actwin_com
http://www.actwin.com/mailman/listinfo.cgi/aquatic-plants