The Sites of Evaporation within Leaves.
The sites of evaporation within leaves are unknown, but they have drawn attention for decades due to their perceived implications for many factors, including patterns of leaf isotopic enrichment, the maintenance of mesophyll water status, stomatal regulation, and the interpretation of measured stomatal and leaf hydraulic conductances. We used a spatially explicit model of coupled water and heat transport outside the xylem, MOFLO 2.0, to map the distribution of net evaporation across leaf tissues in relation to anatomy and environmental parameters. Our results corroborate earlier predictions that most evaporation occurs from the epidermis at low light and moderate humidity but that the mesophyll contributes substantially when the leaf center is warmed by light absorption, and more so under high humidity. We also found that the bundle sheath provides a significant minority of evaporation (15% in darkness and 18% in high light), that the vertical center of amphistomatous leaves supports net condensation, and that vertical temperature gradients caused by light absorption vary over 10-fold across species, reaching 0.3°C. We show that several hypotheses that depend on the evaporating sites require revision in light of our findings, including that experimental measurements of stomatal and hydraulic conductances should be affected directly by changes in the location of the evaporating sites. We propose a new conceptual model that accounts for mixed-phase water transport outside the xylem. These conclusions have far-reaching implications for inferences in leaf hydraulics, gas exchange, water use, and isotope physiology.
Plant Breeding Institute, Sydney Institute of Agriculture, University of Sydney, Narrabri 2390, Australia (T.N.B.); and t.buckley@sydney.edu.au.|Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.) t.buckley@sydney.edu.au.
Thomas N
0000-0001-7610-7136
TN
Buckley
Plant Breeding Institute, Sydney Institute of Agriculture, University of Sydney, Narrabri 2390, Australia (T.N.B.); and.|Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.).
Grace P
0000-0002-8045-5982
GP
John
Plant Breeding Institute, Sydney Institute of Agriculture, University of Sydney, Narrabri 2390, Australia (T.N.B.); and.|Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.).
Christine
0000-0002-2680-3608
C
Scoffoni
Plant Breeding Institute, Sydney Institute of Agriculture, University of Sydney, Narrabri 2390, Australia (T.N.B.); and.|Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 (G.P.J., C.S., L.S.).
Lawren
L
Sack
D000465:Algorithms; D001692:Biological Transport / Q000502:physiology / Q000528:radiation effects; D003198:Computer Simulation; D006813:Humidity; D008027:Light; D058503:Mesophyll Cells / Q000378:metabolism / Q000502:physiology; D008954:Models, Biological; D019441:Plant Epidermis / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D054046:Plant Stomata / Q000378:metabolism; D018526:Plant Transpiration / Q000502:physiology* / Q000528:radiation effects; D010944:Plants / Q000145:classification / Q000378:metabolism*; D013045:Species Specificity; D013696:Temperature; D014867:Water / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism
D014867:Water