The role of freezing in setting the latitudinal limits of mangrove forests.
Mangrove trees dominate coastal vegetation in tropical regions, but are completely replaced by herbaceous salt marshes at latitudes above 32 degrees N and 40 degrees S. Because water deficit can increase damage caused by freezing, we hypothesized that mangroves, which experience large deficits as a result of saline substrates, would suffer freeze-induced xylem failure. Vulnerability to freeze-induced xylem embolism was examined in the most poleward mangrove species in North America, in an area where freezing is rare but severe, and in Australia, in an area where freezing is frequent but mild. Percentage loss in hydraulic conductivity was measured following manipulations of xylem tension; xylem sap ion concentration was determined using X-ray microanalysis. Species with wider vessels suffered 60-100% loss of hydraulic conductivity after freezing and thawing under tension, while species with narrower vessels lost as little as 13-40% of conductivity. These results indicate that freeze-induced embolism may play a role in setting the latitudinal limits of distribution in mangroves, either through massive embolism following freezing, or through constraints on water transport as a result of vessel size.
Stuart
S A
SA
Department of Organismic and Evolutionary Biology, Harvard University, Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, USA.|Present address: Department of Integrative Biology, 3960 Valley Life Sciences Building #3140, University of California, Berkeley, CA 94702, USA.
Choat
B
B
Department of Organismic and Evolutionary Biology, Harvard University, Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Martin
K C
KC
Ecosystem Dynamics Group, Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, Canberra, ACT, 0200, Australia.
Holbrook
N M
NM
Department of Organismic and Evolutionary Biology, Harvard University, Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Ball
M C
MC
Ecosystem Dynamics Group, Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, Canberra, ACT, 0200, Australia.
D032407:Avicennia / Q000033:anatomy & histology / Q000502:physiology*; D005615:Freezing; D053147:Plant Exudates / Q000737:chemistry; D018547:Plant Stems / Q000502:physiology; D043982:Rhizophoraceae / Q000033:anatomy & histology / Q000502:physiology*; D013997:Time Factors; D014197:Trees / Q000502:physiology*; D052584:Xylem / Q000737:chemistry / Q000502:physiology
D053147:Plant Exudates