Leaf colour in autumn

David R. Hershey dh321 at PGSTUMAIL.PG.CC.MD.US
Tue Oct 22 01:35:00 EST 1996


Lack of nitrogen is generally more limiting to plant growth than magnesium
in part because plants require a larger amount of nitrogen relative to
magnesium. The majority of nitrogen must also enter the biosphere via
nitrogen-fixing bacteria while magnesium comes from soil minerals. The
nitrogen store in soils is mainly in the form of organic matter which
slowly releases nitrogen as it decays. Nitrate is also more easily lost
from soils via leaching or denitrification. Cationic magnesium is fairly
resistant to leaching because it is held by the soil's cation exchange 
sites. 

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David R. Hershey
					
Snail mail: 6700 Belcrest Road #112, Hyattsville, MD 20782-1340

Adjunct Professor, Biology/Horticulture Department
Prince George's Community College, Largo, MD 20772-2199

Email: dh321 at pgstumail.pg.cc.md.us
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On 20 Oct 1996, Char A Bezanson wrote:

> Thanks for the summary.  Just one question- I've always been under the
> impression that it was the Mg ion in the center of each chorophyll
> molecule that is the primary object of recycling by trees before
> leaf-drop.  Since Mg++ occupies essentially the same position as Fe++ in
> hemoglobin, its lack would cause the plant equivalent of "iron-poor
> blood"...although I'm sure N is worth retrieving as well.  Do any of the
> plant physiologists out there have any comment on the relative scarcity of
> Mg and N, and of their fate and storage over winter? 
> 
> Char A. Bezanson (bezanson at stolaf.edu)
> School Nature Area Project
> St. Olaf College
> Northfield,  MN  55057
> 
> 
> 



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