compensation point and senescence?

[Janice M. Glime]

If a plant is in a situation where CO2 concentration is below the CO2
compensation point, it means the plant will use more CO2 in respiration
that it will fix in photosynthesis.  Yes, in a sense it does starve.  I am
having difficulty interpreting your question about becoming a sink.  If it
has too little CO2, how could it become a sink for CO2?  Help me out with
your thinking here - perhaps I can help a little more.
Janice
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 Janice M. Glime, Professor  
 Department of Biological Sciences
 Michigan Technological University
 Houghton, MI 49931-1295
 jmglime at mtu.edu
 906-487-2546
 FAX 906-487-3167 
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 > 
> Here's a question Doug Bielenberg and I have been pondering that might
> be interesting for the group to consider:
> What is the mechanism by which a plant recognizes that a leaf is below
> the CO2 compensation point?  This is often used to explain why shaded
> leaves begin to senesce.  Why doesn't the leaf just become a sink for
> carbon?  It doesn't just starve does it?  If the CO2 compensation point
> or a negative carbon budget is the cue for leaf senescence what is the
> mechanism?  It may be pertinent to recall that leaves can have functions
> other than just carboon acquisition; e.g. nutrient stores used for
> growth elsewhere in the plant, transpirational "sinks" driving nutrient
> uptake, modifiers of canopy microclimate, etc. etc.
> Any ideas on this topic?
> John Skillman
> 
> 
>