Size and function in conifer tracheids and angiosperm vessels
Tóm tắt
The wide size range of conifer tracheids and angiosperm vessels has important consequences for function. In both conduit types, bigger is better for conducting efficiency. The gain in efficiency with size is maximized by the control of conduit shape, which balances end‐wall and lumen resistances. Although vessels are an order of magnitude longer than tracheids of the same diameter, they are not necessarily more efficient because they lack the low end‐wall resistance of tracheids with torus‐margo pits. Instead, vessels gain conducting efficiency over tracheids by achieving wider maximum diameters. End‐walls contributed 56–64% to total xylem resistance in both conduit types, indicating that length limits conducting efficiency. Tracheid dimensions may be more limited by unicellularity and the need to supply strength to homoxylous wood than by the need to protect against cavitation. In contrast, the greater size of the multicellular vessel is facilitated by fibers that strengthen heteroxylous wood. Vessel dimensions may be most limited by the need to restrict intervessel pitting and cavitation by air‐seeding. Stressful habitats that promote narrow vessels should favor coexistence of conifers and angiosperms. The evolution of vessels in angiosperm wood may have required early angiosperms to survive a phase of mechanic and hydraulic instability.
Từ khóa
Tài liệu tham khảo
Baas P., 1986, On the economy of plant form and function, 327
Bisset I. J., 1951, The relation of differential collapse and shrinkage to wood anatomy in Eucalyptus regnans F. v. M. and E. Gigantea Hook. F., Australian Journal of Applied Science, 2, 175
Cronquist A., 1988, The evolution and classification of flowering plants
Liese W., 1965, Cellular ultrastructure of woody plants, 271
Mayr S. Hacke U. Schmid P. Schwienbacher F. andGruber A.In press.frost drought in conifers at the alpine timberline: xylem dysfunction and adaptations.Ecology..
Niklas K. J., 1994, Plant allometry
Panshin A. J., 1970, Textbook of wood technology
Vincent J. F. V., 1991, Biomechanics and evolution, 21