I understand basically how water transport from roots to leaves through the xylem works, but I have no idea of the timescales involved.

How long does it take for water to get from root tips to leaves? How does this speed change in different parts of the plant? How does it differ between different plant types? How is it affected by plant size?

Also, I guess it changes from relatively fast in the middle of the day to almost zero at night, but how does it change during a normal sunny day (e.g. sinusoidal? More like a square wave?)

  • $\begingroup$ Could someone please tag this "water" and "xylem" and then delete this comment? $\endgroup$ – naught101 Nov 10 '15 at 23:47
  • $\begingroup$ You can retain this when you edit your question. $\endgroup$ – TanMath Nov 11 '15 at 5:12
  • $\begingroup$ We usually use more general tags and not down to a very fine characterisation of the question. So plant-physiology is fine here. $\endgroup$ – Chris Nov 11 '15 at 7:14
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    $\begingroup$ @user137: Wrong. There is part of the water not evaporating but going down in phloem sap, boundless.com/biology/textbooks/boundless-biology-textbook/… $\endgroup$ – Joce Nov 11 '15 at 14:40
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    $\begingroup$ @user137: Do you have data showing that it is a good approximation? It seems to me that water efficiency would imply an evaporation much smaller than sap flux. This wouldn't contradict pore-pressure driven sap flow, although of course there is always some unavoidable evaporation for this process. $\endgroup$ – Joce Nov 12 '15 at 15:52

You can find some answers for your questions in this paper (it is only for Ricinus communis, but you may follow the cited by from google and find for other plants):


velocity in the phloem (0·250 ± 0·004 mm s−1)
xylem in the light (0·401 ± 0·004 mm s−1), in the dark (0·255 ± 0·003 mm s−1)

Graphs on daily change are on the paper.

  • $\begingroup$ Great, thanks! That's about 1.5m/h in the light, and Castor plants get to a few meters, so I guess it might take a few hours to get from root tips to stomata. $\endgroup$ – naught101 Nov 17 '15 at 0:19

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