Torus-margo pits help conifers compete with angiosperms.
The unicellular conifer tracheid should have greater flow resistance per length (resistivity) than the multicellular angiosperm vessel, because its high-resistance end-walls are closer together. However, tracheids and vessels had comparable resistivities for the same diameter, despite tracheids being over 10 times shorter. End-wall pits of tracheids averaged 59 times lower flow resistance on an area basis than vessel pits, owing to the unique torus-margo structure of the conifer pit membrane. The evolution of this membrane was as hydraulically important as that of vessels. Without their specialized pits, conifers would have 38 times the flow resistance, making conifer-dominated ecosystems improbable in an angiosperm world.
Pittermann
Jarmila
J
Department of Biology, University of Utah, 257S 1400E, Salt Lake City, UT 84112, USA.
Sperry
John S
JS
Hacke
Uwe G
UG
Wheeler
James K
JK
Sikkema
Elzard H
EH
D000222:Adaptation, Physiological; D005075:Biological Evolution; D001692:Biological Transport; D019684:Magnoliopsida / Q000502:physiology; D008566:Membranes / Q000502:physiology; D018514:Plant Structures / Q000502:physiology; D064028:Tracheophyta / Q000033:anatomy & histology / Q000502:physiology*; D014197:Trees / Q000502:physiology; D014867:Water
D014867:Water