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Barbour MM, Farquhar GD, Buckley TN. Leaf water stable isotopes and water transport outside the xylem. PLANT, CELL & ENVIRONMENT 2017; 40:914-920. [PMID: 27739589 DOI: 10.1111/pce.12845] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Revised: 09/12/2016] [Accepted: 09/19/2016] [Indexed: 06/06/2023]
Abstract
How water moves through leaves, and where the phase change from liquid to vapour occurs within leaves, remain largely mysterious. Some time ago, we suggested that the stable isotope composition of leaf water may contain information on transport pathways beyond the xylem, through differences in the development of gradients in enrichment within the various pathways. Subsequent testing of this suggestion provided ambiguous results and even questioned the existence of gradients in enrichment within the mesophyll. In this review, we bring together recent theoretical developments in understanding leaf water transport pathways and stable isotope theory to map a path for future work into understanding pathways of water transport and leaf water stable isotope composition. We emphasize the need for a spatially, anatomically and isotopically explicit model of leaf water transport.
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Affiliation(s)
- M M Barbour
- Centre for Carbon, Water and Food, University of Sydney, Brownlow Hill, New South Wales, 2570, Australia
| | - G D Farquhar
- Research School of Biology, Australian National University, Acton, Australian Capital Territory, 0200, Australia
| | - T N Buckley
- Plant Breeding Institute, Faculty of Agriculture and Environment, The University of Sydney, Narrabri, New South Wales, 2390, Australia
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Buckley TN, John GP, Scoffoni C, Sack L. How Does Leaf Anatomy Influence Water Transport outside the Xylem? PLANT PHYSIOLOGY 2015; 168:1616-35. [PMID: 26084922 PMCID: PMC4528767 DOI: 10.1104/pp.15.00731] [Citation(s) in RCA: 128] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 06/15/2015] [Indexed: 05/18/2023]
Abstract
Leaves are arguably the most complex and important physicobiological systems in the ecosphere. Yet, water transport outside the leaf xylem remains poorly understood, despite its impacts on stomatal function and photosynthesis. We applied anatomical measurements from 14 diverse species to a novel model of water flow in an areole (the smallest region bounded by minor veins) to predict the impact of anatomical variation across species on outside-xylem hydraulic conductance (Kox). Several predictions verified previous correlational studies: (1) vein length per unit area is the strongest anatomical determinant of Kox, due to effects on hydraulic pathlength and bundle sheath (BS) surface area; (2) palisade mesophyll remains well hydrated in hypostomatous species, which may benefit photosynthesis, (3) BS extensions enhance Kox; and (4) the upper and lower epidermis are hydraulically sequestered from one another despite their proximity. Our findings also provided novel insights: (5) the BS contributes a minority of outside-xylem resistance; (6) vapor transport contributes up to two-thirds of Kox; (7) Kox is strongly enhanced by the proximity of veins to lower epidermis; and (8) Kox is strongly influenced by spongy mesophyll anatomy, decreasing with protoplast size and increasing with airspace fraction and cell wall thickness. Correlations between anatomy and Kox across species sometimes diverged from predicted causal effects, demonstrating the need for integrative models to resolve causation. For example, (9) Kox was enhanced far more in heterobaric species than predicted by their having BS extensions. Our approach provides detailed insights into the role of anatomical variation in leaf function.
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Affiliation(s)
- Thomas N Buckley
- I.A. Watson Grains Research Centre, Faculty of Agriculture and Environment, University of Sydney, Narrabri, New South Wales 2390, Australia (T.N.B.); andDepartment of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.)
| | - Grace P John
- I.A. Watson Grains Research Centre, Faculty of Agriculture and Environment, University of Sydney, Narrabri, New South Wales 2390, Australia (T.N.B.); andDepartment of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.)
| | - Christine Scoffoni
- I.A. Watson Grains Research Centre, Faculty of Agriculture and Environment, University of Sydney, Narrabri, New South Wales 2390, Australia (T.N.B.); andDepartment of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.)
| | - Lawren Sack
- I.A. Watson Grains Research Centre, Faculty of Agriculture and Environment, University of Sydney, Narrabri, New South Wales 2390, Australia (T.N.B.); andDepartment of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.)
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