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Title: Unsaturation of vapour pressure inside leaves of two conifer species

Stomatal conductance (g s) impacts both photosynthesis and transpiration, and is therefore fundamental to the global carbon and water cycles, food production, and ecosystem services. Mathematical models provide the primary means of analysing this important leaf gas exchange parameter. A nearly universal assumption in such models is that the vapour pressure inside leaves (e i) remains saturated under all conditions. The validity of this assumption has not been well tested, because so far e i cannot be measured directly. Here, we test this assumption using a novel technique, based on coupled measurements of leaf gas exchange and the stable isotope compositions of CO 2 and water vapour passing over the leaf. We applied this technique to mature individuals of two semiarid conifer species. In both species, e i routinely dropped below saturation when leaves were exposed to moderate to high air vapour pressure deficits. Typical values of relative humidity in the intercellular air spaces were as low 0.9 in Juniperus monosperma and 0.8 in Pinus edulis. These departures of e i from saturation caused significant biases in calculations of g s and the intercellular CO 2 concentration. Thus, our results refute the longstanding assumption of saturated vapour pressure in plantmore » leaves under all conditions.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [6] ; ORCiD logo [5] ;  [2] ;  [7] ;  [2]
  1. James Cook Univ., Cairns, QLD (Australia). College of Science and Engineering
  2. Australian National Univ., Canberra, ACT (Australia). Research School of Biology
  3. Univ. of California, Santa Cruz, CA (United States). Dept. of Ecology and Evolutionary Biology
  4. METER Group, Inc., Pullman, WA (United States)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  6. Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Biology
  7. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Earth Systems Analysis and Modelling Group
Publication Date:
Report Number(s):
LA-UR-17-30329
Journal ID: ISSN 2045-2322
Grant/Contract Number:
AC52-06NA25396; DP1097276; DP150100588
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 8; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Laboratory Directed Research and Development (LDRD) Program
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; Biological Science; stomatal control, leaf gas exchange, pinon, juniper, drought
OSTI Identifier:
1440441