Go to OSU College of Forestry LWGate Home Page.From: "Andrew K Fletcher" <Gravity@blueyonder.co.uk>
Subject: RE: [IAWA Forum] Fluid density altered by evaporation at the leaf?
Date: Wed, 5 Apr 2006 09:35:16 +0100
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This is a multi-part message in MIME format. ------=_NextPart_000_007C_01C65894.3F223B90 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Paul The salt exuding plants like Mangrove are firm evidence for the location = of concentrated fluids in the leaves and upper branches of the tree. = Maybe the exuding salt plants have to be more efficient at transporting = higher volumes of salts due to environmental factors. So the density of = the xylem sap should be significantly higher in mangrove than a tree = with significantly higher concentrations of water molecules in the soil = water. It should as you say be possible to calculate a dynamic salt budget. = This could be tested by increasing the density of the soil water to the = point that the tree wilts, and the reverse should also be possible by = increasing the water molecules of the soil water to the point where the = wilting stops and the tree restores the lost fluids. A 3% increase in both salt / or / and sugar density at the leaves is = very significant. The molecular weight of said salts and sugars at the = top of the tree will inevitably cause an imbalance with sap in close = proximity and initiate the movement of the denser sap. I agree with you that it does not matter about the exact fraction of = water that is lost through transpiration, more water loss =3D more water = pulled in to replace the lost water and higher volumes of dilute sap = flowing through the leaves. Andrew I was wondering if maybe from the nutrient standpoint, it doesn't matter = so much the exact fraction of water that is passing straight through = (the 99%) as long as it is nearly all, but that none of the salts leave = through transpiration (except from those salt plants that exude salts). = So one could in principal calculate a sort of dynamic salt budget = incorporating input rate through the roots, the plant growth (expanding = symplasm volume), and salt loss through shedding of plant parts. I believe the density of water only increases by about 3% (at 25 deg-C) = going from pure to 1 molal NaCl. The inside of leaf parenchyma cells = must see those kind of solute concentrations, but I believe the xylem = sap is thought of as much more dilute. Seems like the living cells must = be stripping the xylem of its solutes before the transpiration stream = reaches the stomata or we'd see crusts around stomata or substomatal = cavities. Then there's those salt plants... Paul Schulte Simcha, Thank you for elaborating. I agree with you on the phloem being a route to a sink and for = identifying the drop off sites for the many types of molecules found in the sap. Do you agree that the massive loss of water vapour in the transpiring = tree=20 must have an effect on the sap it evaporates from? Andrew I think that the phloem must be a strong sink, directly or via various = types of living cells. There are many types of molecules involved with various = types of sinks and specific transporters. Some are moved by the phloem to sinks = such as cambial activity or developing fruit and leaves. Others turn into = polymers that may later turn into monomers (e.g., starch) but others may be = "buried" in lignin which is an end product. Silicon can turn into opal and be = deposited in special cells or cover the epidermis. There are many roads to Rome. I = don't think that a single, simple solution can explain this complicated = phenomenon. Simcha ------=_NextPart_000_007C_01C65894.3F223B90 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=3DContent-Type content=3D"text/html; = charset=3Diso-8859-1"> <META content=3D"MSHTML 6.00.2900.2802" name=3DGENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=3D#ffffff><FONT face=3DArial size=3D2> <P><FONT face=3D"Times New Roman" size=3D3>Paul</FONT></P> <P><FONT face=3D"Times New Roman" size=3D3>The salt exuding plants like = Mangrove are=20 firm evidence for the location of concentrated fluids in the leaves and = upper=20 branches of the tree. Maybe the exuding salt plants have to be more = efficient at=20 transporting higher volumes of salts due to environmental factors. So = the=20 density of the xylem sap should be significantly higher in mangrove than = a tree=20 with significantly higher concentrations of water molecules in the soil=20 water.</FONT></P> <P><FONT face=3D"Times New Roman" size=3D3>It should as you say be = possible to=20 calculate a dynamic salt budget. This could be tested by increasing the = density=20 of the soil water to the point that the tree wilts, and the reverse = should also=20 be possible by increasing the water molecules of the soil water to the = point=20 where the wilting stops and the tree restores the lost = fluids.</FONT></P> <P><FONT face=3D"Times New Roman" size=3D3>A 3% increase in both salt / = or / and=20 sugar density at the leaves is very significant. The molecular weight of = said=20 salts and sugars at the top of the tree will inevitably cause an = imbalance with=20 sap in close proximity and initiate the movement of the denser = sap.</FONT></P> <P><FONT face=3D"Times New Roman" size=3D3>I agree with you that it does = not matter=20 about the exact fraction of water that is lost through transpiration, = more water=20 loss =3D more water pulled in to replace the lost water and higher = volumes of=20 dilute sap flowing through the leaves.</FONT></P> <P><FONT face=3D"Times New Roman" size=3D3>Andrew</FONT></P> <P><BR><BR><FONT face=3D"Times New Roman" size=3D3>I was wondering if = maybe from the=20 nutrient standpoint, it doesn't matter so much the exact fraction of = water that=20 is passing straight through (the 99%) as long as it is nearly all, but = that none=20 of the salts leave through transpiration (except from those salt plants = that=20 exude salts). So one could in principal calculate a sort of dynamic salt = budget=20 incorporating input rate through the roots, the plant growth (expanding = symplasm=20 volume), and salt loss through shedding of plant parts.<BR><BR>I believe = the=20 density of water only increases by about 3% (at 25 deg-C) going from = pure to 1=20 molal NaCl. The inside of leaf parenchyma cells must see those kind of = solute=20 concentrations, but I believe the xylem sap is thought of as much more = dilute.=20 Seems like the living cells must be stripping the xylem of its solutes = before=20 the transpiration stream reaches the stomata or we'd see crusts around = stomata=20 or substomatal cavities. Then there's those salt plants...<BR><BR>Paul=20 Schulte</FONT></P><SPAN=20 style=3D"FONT-SIZE: 12pt; FONT-FAMILY: 'Times New Roman'; = mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-GB; = mso-fareast-language: EN-US; mso-bidi-language: AR-SA"> <DIV><BR><FONT face=3DArial size=3D2>Simcha, </FONT>Thank you for = elaborating.<BR>I=20 agree with you on the phloem being a route to a sink and for = identifying<BR>the=20 drop off sites for the many types of molecules found in the sap.<BR>Do = you agree=20 that the massive loss of water vapour in the transpiring tree <BR>must = have an=20 effect on the sap it evaporates from?</DIV> <DIV>Andrew</DIV> <DIV> </DIV> <DIV> <P class=3DMsoNormal style=3D"MARGIN: 0cm 0cm 0pt">I think that the = phloem must be a=20 strong sink, directly or via various types of<BR>living cells. = There are=20 many types of molecules involved with various types of<BR>sinks and = specific=20 transporters. Some are moved by the phloem to sinks such = as<BR>cambial=20 activity or developing fruit and leaves. Others turn into = polymers<BR>that=20 may later turn into monomers (e.g., starch) but others may be "buried"=20 in<BR>lignin which is an end product. Silicon can turn into opal = and be=20 deposited in<BR>special cells or cover the epidermis. There are = many roads=20 to Rome. I don=92t<BR>think that a single, simple solution can = explain this=20 complicated phenomenon.<BR>Simcha<SPAN lang=3DEN-US=20 style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial; = mso-ansi-language: EN-US"><?xml:namespace=20 prefix =3D o ns =3D "urn:schemas-microsoft-com:office:office"=20 /><o:p></o:p></SPAN></P></SPAN></FONT></DIV></BODY></HTML> ------=_NextPart_000_007C_01C65894.3F223B90-- ======== Welcome All Anatomists! ========== About this IAWA Discussion Group, subscribing, unsubscribing, and archives: http://www.cof.orst.edu/org/IAWA About the IAWA and/or the IAWA Journal: http://www.kuleuven.ac.be/bio/sys/iawa The International Association of Wood Anatomists
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