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Title: Effect of Leaf Water Potential on Internal Humidity and CO 2 Dissolution: Reverse Transpiration and Improved Water Use Efficiency under Negative Pressure

The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but with much lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flat surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO 2, thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO 2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Here, our results indicate that the reduction inmore » vapor pressures of water and CO 2 could enhance plant water use efficiency up to about 10% at a leaf water potential of -2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. Lastly, the omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO 2 concentration based on leaf gas exchange measurements. Manufactures of leaf gas exchange measurement systems should incorporate leaf water potentials in measurement set-ups.« less
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [4] ;  [4]
  1. Univ. of Helsinki (Finland). Dept. of Physics; Univ. of Helsinki (Finland). Dept. of Forest Sciences; Univ. of Helsinki (Finland). Viikki Plant Science Centre
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of Helsinki (Finland). Dept. of Physics
  4. Univ. of Helsinki (Finland). Dept. of Forest Sciences
Publication Date:
Report Number(s):
Journal ID: ISSN 1664-462X
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Frontiers in Plant Science
Additional Journal Information:
Journal Volume: 8; Journal ID: ISSN 1664-462X
Frontiers Research Foundation
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Laboratory Directed Research and Development (LDRD) Program; Academy of Finland Centre of Excellence
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; Biological Science; Earth Sciences; Kelvin effect; foliar water uptake; vapor pressure deficit; water potential; CO2 assimilation; carbon uptake; water uptake; water use efficiency; redwood
OSTI Identifier: