(Fwd) Re: [IAWA Forum] Radial water transport

From: "Richard Jagels" <Richard_Jagels@apollo.umenfa.maine.edu>
Subject: (Fwd) Re: [IAWA Forum] Radial water transport
Date: Mon, 7 Oct 2002 15:34:46 -0500

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------- Forwarded message follows -------
From:           	Richard Jagels <Richard_Jagels@apollo.umenfa.maine.edu>
To:             	"Gartner, Barbara" <Barbara.Gartner@orst.edu>
Subject:        	Re: [IAWA Forum] Radial water transport
Date sent:      	Mon, 7 Oct 2002 09:14:32 -0500

Hi Barbara,

I haven't actually given much thought to radial water transport in
conifers, but here are some comments:

1.  In Metsequoia, a tree easily drought stressed, the evidence seems
to suggest little radial transport.  When a drought stressed tree is
cut in late summer and a radial section of sapwood is examined we see
narrow  bands of saturated wood intermixed with bands of dry wood.  I
see this as a protedtive mechanism (preventing complete loss of water
columns).

2.  Since files of tracheids bend into branches, a lack of efficient
radial transport of water may allow  the tree to maintain water
columns (sheaths) to the top of the tree while cutting off water to
lower branches.

3.  Maintaining somewhat independent colums of water may help in
recharging sapwood water at night.  As the column pressures become
less negative lateral diffusion could recharge adjacent dry columns. 
This would be more energy efficient than vertically reestablishing
columns.

One could argue that bordered pits in tangential walls could serve the
same purpose, but the problem with this argument is that bordered pits
are purely passive valves, so I can't envision a mechanism that would
allow  closing of tangential wall pits without also closing all pits
and thus stopping vertical water transport.

I'd be interested in your comments on this.

Dick Jagels

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