🚀 go-pugleaf

In article <1992Jan2.182754.29872@mcs.anl.gov>, tim@spatial.uucp (Tim
Eckert) writes:In article <1992Jan2.182754.29872@mcs.anl.gov>,
tim@spatial.uucp (Tim Eckert) writes:
|>   Does anyone have some handy references on uptake factors for
|> nitrates from soil to plants?  All of the literature I can find
|> only seems to discuss how nitrogen levels in the soil affect
|> uptake of other metals and chemicals into plants.
|> 
|>   I've been told to assume that the concentration in the plant
|> is equal to the concentration in the soil.  
   ^^^^^^^^^^^^
Not a good idea for several reasons:

1) Nitrate is actively transported into roots from the 
rhizosphere.  Photosynthate supply to roots influences the
rate of transport.  Diffusion across the resulting 
concentration gradient controls the rate at which nitrate 
reaches the root surface.

2) Nitrate is quickly reduced to an amine and incorporated
in free amino acids and eventually protein--so what is the
"nitrate concentration" in the plant?

3) Many wild (non-agricultural) plants not only thrive in
environments with very low levels of detectable nitrate in 
the soil, but take up ammonium in preference to nitrate if
both are present.

4) Nitrogen concentrations vary greatly among different
plant parts, e.g. high in leaves and reproductive organs,
low in roots, very low in woody stems.

5) In many long-lived plants, retranslocation from leaves,
small branches, and fine roots before they are shed, is a
major source of nitrogen for new growth.

6) Although nitrate tends to stay in soil solution.  Most 
nitrogen used by plants is *not* in the soil solution for 
long.  Rather it is mineralized from organic material, at
a rate dependent on temperature, moisture, carbon:nitrogen
ratios, and lignin content (primarily), and is only briefly 
present in the soil solution before being taken up by plants
or soil microorganisms.  Mineralization rates are widely 
viewed as more useful measures of nitrogen supply than 
solution concentrations.  Organic nitrogen mineralized to 
ammonium may or may not get oxidized to nitrate before uptake 
by plants or loss in gaseous forms.

7) For a given level of soil nitrogen supply, concentrations 
in leaves are influenced by root:shoot ratios.  More root
surface area per g leaf generally implies more N per g leaf.

And all that ignores complications associated with nitrogen
fixation in root nodules.

|>I need some 
|> references to verify this or get a new uptake factor.  I
|> appreciate your help.
|> 

This is nowhere near as clean as having an "uptake factor"
sorry.

Some useful references:

Nobel, P.S. 1991. Physiochemical and environmental plant 
physiology.  Academic Press, San Diego.

Fitter, A.H. and R.K.M. Hay. 1987. Environmental physiology
of plants, 2nd Ed.  Academic Press, London.

Charles-Edwards, D.A., D. Doley, G.M. Rimmington. 1986. 
Modeling plant growth and development. Academic Press,
Syndey. --this one is closest to having a suitable simple 
uptake model (pp. 144-146).

Haynes, R.J., K.C. Cameron, K.M. Goh, R.R. Sherlock. 1986.
Mineral nitrogen in the plant--soil system. Academic Press,
Orlando. --see chapter 6: Uptake and assimilation of mineral
nitrogen by plants, text pp. 303-358, references pp. 358-378.

|> Tim Eckert
|> tim@spatial.eid.anl.gov
|> 


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