I need to know.

Thanks

I would not apply those exact terms to roots. Instead, I would say
roots can excrete acids or bases depending on the environment. Also,
roots have a cation exchange capacity.

Tree roots should be able to excrete acid (hydrogen ions) or bases
(hydroxyl ions or carbonate ions) depending on the ionic composition
of the soil solution.

If most or all of the nitrogen is present as nitrate (NO3-), then
roots excrete hydroxyl ions (OH-). With all nitrogen as NO3-, roots
generally take up more anions than cations so must excrete some OH- to
maintain cation-anion balance. The hydroxyl ions may cause the soil
solution pH to rise. Roots have to have a net cation uptake about
equal to the net anion uptake on a charge basis in order to maintain
electroneutrality.

If a significant amount of nitrogen is present as ammonium (NH4+),
then most roots excrete hydrogen ions (H+) . With a significant amount
of NH4+, roots generally take up more cations than anions so must
excrete some H+ to maintain cation-anion balance. The hydrogen ions
cause the soil solution pH to decline.

In some species of iron-efficient plants, the roots excrete large
quantities of H+ even with all nitrogen as nitrate. This occurs when
the plants become iron deficient. The decline in rootzone pH greatly
increase iron availability. The shrub, Euonymus japonica, responds to
iron deficiency in this way (Hershey and Paul 1983).

In common philodendron (Philodendron scandens ssp. oxycardium), the
roots excrete H+ and the soil solution pH declines even when all
nitrogen is provided as nitrate. This pH decline occurs even when the
plant is not iron deficient (Mattis and Hershey 1992).

The above phenomena have not been studied for too many species.

Roots have a cation exchange capacity because of negative charges on
their cellulose surfaces which are satisfied by cations, such as
calcium (Ca++). Roots have an absolute requirement for calcium and
boron in the external solution to maintain membrane integrity.


References

Hershey, D.R. and Paul, J.L. 1983. Ion absorption by a woody plant
with episodic growth. HortScience 18: 357-359.

Hershey, D.R. 1986. Iron deficiency stress response of Tolmiea
menziesii. Journal of Plant Nutrition 14:1145-1150.

Hershey, D.R. 1992. Plant nutrient solution pH changes. Journal of
Biological Education 26:107-111.

Mattis, P. R. and Hershey, D.R. 1992. Iron deficiency stress response
of Epipremnum aureum and Philodendron scandens subspecies oxycardium.
Journal of Plant Physiology 139: 498-502.

Nye, P.H. 1986. Acid-base changes in the rhizosphere. Advances in
Plant Nutrition 2: 129-153.

Cation specific exchange capacity of cell wall material isolated from
roots of plant species differing in Al resistance:
http://www.ipe.uni-hannover.de/publi...in_poster1.pdf

Thank you very much for this.

We are a small chemical company trying to develop a poison to kill localized
tree roots in sewer and storm-water drains.

Given the inaccessibility of these roots, we need a specific poison attached
to a cationic/anionic/acidic/basic/charge-transfer polymer to be
absorbed/adsorbed by these roots with a single transient pass of delivery
fluid. We are thinking along the lines of a heavy-metal ligand compound
such as Cr or Cu, and for experimental purposes a dye included to gauge root
absorption of the compound.



"David Hershey" wrote in message
om...
I would not apply those exact terms to roots. Instead, I would say
roots can excrete acids or bases depending on the environment. Also,
roots have a cation exchange capacity.

Tree roots should be able to excrete acid (hydrogen ions) or bases
(hydroxyl ions or carbonate ions) depending on the ionic composition
of the soil solution.

If most or all of the nitrogen is present as nitrate (NO3-), then
roots excrete hydroxyl ions (OH-). With all nitrogen as NO3-, roots
generally take up more anions than cations so must excrete some OH- to
maintain cation-anion balance. The hydroxyl ions may cause the soil
solution pH to rise. Roots have to have a net cation uptake about
equal to the net anion uptake on a charge basis in order to maintain
electroneutrality.

If a significant amount of nitrogen is present as ammonium (NH4+),
then most roots excrete hydrogen ions (H+) . With a significant amount
of NH4+, roots generally take up more cations than anions so must
excrete some H+ to maintain cation-anion balance. The hydrogen ions
cause the soil solution pH to decline.

In some species of iron-efficient plants, the roots excrete large
quantities of H+ even with all nitrogen as nitrate. This occurs when
the plants become iron deficient. The decline in rootzone pH greatly
increase iron availability. The shrub, Euonymus japonica, responds to
iron deficiency in this way (Hershey and Paul 1983).

In common philodendron (Philodendron scandens ssp. oxycardium), the
roots excrete H+ and the soil solution pH declines even when all
nitrogen is provided as nitrate. This pH decline occurs even when the
plant is not iron deficient (Mattis and Hershey 1992).

The above phenomena have not been studied for too many species.

Roots have a cation exchange capacity because of negative charges on
their cellulose surfaces which are satisfied by cations, such as
calcium (Ca++). Roots have an absolute requirement for calcium and
boron in the external solution to maintain membrane integrity.


References

Hershey, D.R. and Paul, J.L. 1983. Ion absorption by a woody plant
with episodic growth. HortScience 18: 357-359.

Hershey, D.R. 1986. Iron deficiency stress response of Tolmiea
menziesii. Journal of Plant Nutrition 14:1145-1150.

Hershey, D.R. 1992. Plant nutrient solution pH changes. Journal of
Biological Education 26:107-111.

Mattis, P. R. and Hershey, D.R. 1992. Iron deficiency stress response
of Epipremnum aureum and Philodendron scandens subspecies oxycardium.
Journal of Plant Physiology 139: 498-502.

Nye, P.H. 1986. Acid-base changes in the rhizosphere. Advances in
Plant Nutrition 2: 129-153.

Cation specific exchange capacity of cell wall material isolated from
roots of plant species differing in Al resistance:
http://www.ipe.uni-hannover.de/publi...in_poster1.pdf