Abstract Detail

Paleobotany

Decombeix, Anne-Laure [1], Rowe, Nick P [1], Serbet, Rudolph [2], Taylor, Edith L [3].

What is the functional significance of the unusual cambial development in Vertebraria (Glossopteridales) roots? Some geometrical and mechanical clues.

Developmental changes in the onset of secondary growth are a powerful source of variation for the hydraulic and mechanical properties of woody plants. A fascinating example from the fossil record is the Permian morphogenus Vertebraria. Vertebraria axes represent the roots of the glossopteridalean seed plants, which dominated Southern Hemisphere floras during the Permian. In the first stages of their secondary growth, Vertebraria roots typically have a discontinuous production of secondary xylem around the axis. The lengthening of this phenomenon results in a wood cylinder that is discontinuous and appears star-shaped in cross-section, with lacunae between the wedges of wood. In older roots, xylem production becomes continuous around the axis, surrounding the central discontinuous wood development. This unique anatomy of the young developmental stages and the following "inside out" transformation likely has a strong impact on the functional properties of Vertebraria axes.
In this study, we combine new anatomical observations of Vertebraria from the Late Permian of Skaar Ridge, Antarctica, with geometrical and mechanical approaches. We investigate (1) to what extent Vertebraria differs from “normal” roots with a conventional circular outline, and (2) what is the functional significance of its derived organization. Comparisons of tissue distribution in cross-section between a normal root with an entire cylinder of wood and a star-shaped organization show “cheaper” growth in the latter where a smaller number of wood cells are produced to develop a given overall diameter. The star-shaped organization of the wood in young Vertebraria roots also leads to a reduced surface for hydraulic conductivity compared to a normal root but a potentially higher bending rigidity owing to its "I"-beam-like organisation. Young Vertebraria specimens are observed to have grown inside the wood of another trunk suggesting that the star-shaped organization provided a potentially effective method for growth through the surrounding matrix by young roots.
The unique organization of the wood in young Vertebraria roots possibly represents a "light structural organisation" and efficient strategy for fast root growth and rapid establishment in a wet environment such as a peat swamp. The “inside out” transformation to a more classical root anatomy might reflect the prioritization of new functions (such as carbon storage, water transport and strength) in later stages of root development. The ecological implications of these functional strategies in high-latitude peat swamps will be discussed.

1 - CNRS, UMR AMAP, C/o CIRAD, TA A51/PS2, Bvd De La Lironde, Montpellier, N/A, F-34398, France
2 - University Of Kansas, Division Of Paleobotany, NAT HIST MUS & BIODIV RES INST, 1200 Sunnyside Avenue, Lawrence, KS, 66045, USA
3 - University Of Kansas, Department Of Ecology And Evolutionary Biology, 1200 Sunnyside Avenue, Haworth Hall, Lawrence, KS, 66045-7600, USA

Keywords:
Permian
Glossopteridales
Antarctica
anatomy
root
development.

Presentation Type: Oral Paper
Session: 17, Paleozoic and Mesozoic paleobotany
Location: Sundance 3/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 8:30 AM
Number: 17003
Abstract ID:144
Candidate for Awards:None