Xylem traits mediate a trade-off between resistance to freeze—thaw-induced embolism and photosynthetic capacity in overwintering evergreens

• Published in: The New phytologist Vol. 191; no. 4; pp. 996 - 1005
• Main Authors: Choat, Brendan, Medek, Danielle E., Stuart, Stephanie A., Pasquet-Kok, Jessica, Egerton, John J. G., Salari, Hooman, Sack, Lawren, Ball, Marilyn C.
• Format: Journal Article
• Language: English
• Published: Oxford, UK John Wiley & Sons 01.09.2011; Blackwell Publishing Ltd; Wiley Subscription Services, Inc
• Subjects: Adaptation, Physiological; Anatomy; Australia; Biological Transport - physiology; Capacity; Carbon dioxide; cavitation; Cold Temperature; Conductance; Correlation; Embolism; Embolisms; evergreen; Freeze-thawing; Freezing; Gas exchange; Heat exchange; Hot Temperature; Hydraulic conductivity; Hydraulics; Interspecific; Leaves; Magnoliopsida - anatomy & histology; Magnoliopsida - physiology; Overwintering; Photosynthesis; Plant cells; Plant ecology; Plant Leaves - physiology; Plant Stems - physiology; Plant Stomata - physiology; Plant Transpiration; Plants; Resistance; Seasons; Specific conductivity; Stomata; Stomatal conductance; Transport; Winter; Xylem; Xylem - anatomy & histology; Xylem - physiology; Xylem vessels
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2011.03772.x

Hydraulic traits were studied in temperate, woody evergreens in a high-elevation heath community to test for trade-offs between the delivery of water to canopies at rates sufficient to sustain photosynthesis and protection against disruption to vascular transport caused by freeze—thaw-induced embolism. Freeze—thaw-induced loss in hydraulic conductivity was studied in relation to xylem anatomy, leaf- and sapwood-specific hydraulic conductivity and gas exchange characteristics of leaves. We found evidence that a trade-off between xylem transport capacity and safety from freeze—thaw-induced embolism affects photosynthetic activity in over-wintering evergreens. The mean hydraulically weighted xylem vessel diameter and sapwood-specific conductivity correlated with susceptibility to freeze—thaw-induced embolism. There was also a strong correlation of hydraulic supply and demand across species; interspecific differences in stomatal conductance and CO₂ assimilation rates were correlated linearly with sapwood- and leaf-specific hydraulic conductivity. Xylem vessel anatomy mediated an apparent trade-off between resistance to freeze—thaw-induced embolism and hydraulic and photosynthetic capacity during the winter. These results point to a new role for xylem functional traits in determining the degree to which species can maintain photosynthetic carbon gain despite freezing events and cold winter temperatures.