Cavitation Resistance in Seedless Vascular Plants: The Structure and Function of Interconduit Pit Membranes.
Plant water transport occurs through interconnected xylem conduits that are separated by partially digested regions in the cell wall known as pit membranes. These structures have a dual function. Their porous construction facilitates water movement between conduits while limiting the spread of air that may enter the conduits and render them dysfunctional during a drought. Pit membranes have been well studied in woody plants, but very little is known about their function in more ancient lineages such as seedless vascular plants. Here, we examine the relationships between conduit air seeding, pit hydraulic resistance, and pit anatomy in 10 species of ferns (pteridophytes) and two lycophytes. Air seeding pressures ranged from 0.8 ± 0.15 MPa (mean ± sd) in the hydric fern Athyrium filix-femina to 4.9 ± 0.94 MPa in Psilotum nudum, an epiphytic species. Notably, a positive correlation was found between conduit pit area and vulnerability to air seeding, suggesting that the rare-pit hypothesis explains air seeding in early-diverging lineages much as it does in many angiosperms. Pit area resistance was variable but averaged 54.6 MPa s m-1across all surveyed pteridophytes. End walls contributed 52% to the overall transport resistance, similar to the 56% in angiosperm vessels and 64% in conifer tracheids. Taken together, our data imply that, irrespective of phylogenetic placement, selection acted on transport efficiency in seedless vascular plants and woody plants in equal measure by compensating for shorter conduits in tracheid-bearing plants with more permeable pit membranes.
School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511 (C.B.);Institute for Systematic Botany and Ecology, Ulm University, 89081 Ulm, Germany (S.J.);University of Western Sydney, Hawkesbury Institute for the Environment, Richmond, New South Wales 2753, Australia (B.C.); andDepartment of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064 (C.R., J.P.).
Craig
C
Brodersen
School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511 (C.B.);Institute for Systematic Botany and Ecology, Ulm University, 89081 Ulm, Germany (S.J.);University of Western Sydney, Hawkesbury Institute for the Environment, Richmond, New South Wales 2753, Australia (B.C.); andDepartment of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064 (C.R., J.P.).
Steven
S
Jansen
School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511 (C.B.);Institute for Systematic Botany and Ecology, Ulm University, 89081 Ulm, Germany (S.J.);University of Western Sydney, Hawkesbury Institute for the Environment, Richmond, New South Wales 2753, Australia (B.C.); andDepartment of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064 (C.R., J.P.).
Brendan
B
Choat
School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511 (C.B.);Institute for Systematic Botany and Ecology, Ulm University, 89081 Ulm, Germany (S.J.);University of Western Sydney, Hawkesbury Institute for the Environment, Richmond, New South Wales 2753, Australia (B.C.); andDepartment of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064 (C.R., J.P.).
Christopher
C
Rico
School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511 (C.B.);Institute for Systematic Botany and Ecology, Ulm University, 89081 Ulm, Germany (S.J.);University of Western Sydney, Hawkesbury Institute for the Environment, Richmond, New South Wales 2753, Australia (B.C.); andDepartment of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064 (C.R., J.P.) jpitterm@ucsc.edu.
Jarmila
J
Pittermann