Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Not Hydraulic but an Adsorption Water Transport occurs in the Xylem of Land Plants

Version 1 : Received: 23 January 2023 / Approved: 26 January 2023 / Online: 26 January 2023 (03:02:38 CET)

How to cite: Hahn, K. Not Hydraulic but an Adsorption Water Transport occurs in the Xylem of Land Plants. Preprints 2023, 2023010464. Hahn, K. Not Hydraulic but an Adsorption Water Transport occurs in the Xylem of Land Plants. Preprints 2023, 2023010464.


Ad- and desorption forces move water in living xylem/wood from the root to the leaf thermodynamically. The doctrine of plant water transport, the so-called cohesion- or cohesion-tension theory, postulates however that the process is physically based on a hydraulic fluid flow with negative pressure in water conducting tubes originating from the leaves. Lower pressure (suction) driven volume flow is physically a branch of mechanics. Moisture absorbed from the soil via the root is thought to be pulled up the stem by the leaves in continuous and tensioned threads of water. It is assumed that the hydraulic Hagen/Poiseuille flow law, derived for tubes, applies in the xylem. In a textbook of botany you can find the opinion: "Just as the pipes of a water pipe supply necessary water to each household, leaf nerves supply water and nutrient salts to each individual cell.” (Translated from German). Many plant physiologists consider this hydraulic principle to be correct, but it does not remain unchallenged. Doubts are repeatedly expressed. The question arises: How does water transport actually take place? It is shown how the diffusive/adsorption transport principle works. The partial dehydration (desorption) of the plant, driven by the diffusive process of transpiration, forms a combined concentration and adsorption-site gradient for water in the xylem matrix. Especially with open stomata the lowest moisture concentration and the highest number of adsorption-sites for water (sites with free van der Waals forces), can be found in the mesophyll cell walls at the liquid/vapor boundary in the leaf. The water taken up by the root moves spontaneously in the direction of this boundary and can thus partially or completely compensate for the existing concentration- and adsorption-site- differences for water. Thus, a thermodynamic overlapping diffusive/adsorptive movement of moisture along the stationary xylem/wood takes place. After the introduction and a review of some controversies with cohesion theory, the physiology of the processes associated with long-distance water displacement is mentioned below. A thermodynamic adsorption hypothesis of the natural water transport in plants, based on known facts, is presented.


Adsorption water movement; adsorption hypothesis; plant long-distance water transport; thermodynamic water movement; not-hydraulic movement


Biology and Life Sciences, Forestry

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