Abstract Detail

Novel Approaches to Plant Evolution from Paleontological, Physiological, and Developmental Perspectives

Pittermann, Jarmila [1], Baer, Alex [2], Brodersen, Craig [3], Burns, Emily [4], Watkins, James E. [5], Wheeler, James [6].

Water transport in seed-free vascular plants: a macro-evolutionary perspective.

The evolution of vascular tissue was a transformative leap in the colonization of land by plants. Throughout the Devonian, effective water transport and stomatal function not only enabled early-derived seed-free plants to inhabit different niches, but also to explore a broader morphospace by evolving taller and more developed canopies. The fossil record shows that concurrent selection for hydraulic efficiency favoured greater xylem content and progressively larger conduits, traits that supported increasing plant size and complexity throughout this period. However, water transport must strike a balance between hydraulic efficiency and resistance to cavitation, that is the suction of air into water-filled conduits, a phenomenon most commonly associated with periods of drought stress. Little is known about how ancient tracheophytes balanced hydraulic efficiency with cavitation resistance, a situation further complicated by the absence of modern analogues for some of the more unusual taxa. Despite this gap, developing a nuanced understanding of the evolution of plant water transport is possible by using a comparative approach to investigate the functional attributes of extant mosses, ferns and lycophytes, relative to the well-studied xylem of woody plants. Indeed, the xylem of seed-free vascular plants is substantially different: they have no secondary xylem, and transport depends entirely on tracheids. Yet taken together, the structure and function of this primary xylem network exhibits attributes that both converge with and diverge from woody plants. For example, xylem conduit diameters in fern fronds fall within the typical range seen in stems of conifers and angiosperms, but conduit ultrastructure differs substantially. At the organismal level, preliminary data suggest a fundamental co-ordination of scale between xylem (internal) and branching (external) networks that is comparable to conifers and angiosperms, but the reliance on primary xylem limits overall transport capacity and morphological flexibility. Lastly, field studies indicate that perennial ferns can survive extended periods of drought, despite experiencing significant hydraulic failure and frond dieback. Drought tolerance in these plants appears to be a function of stomatal closure and cavitation resistance, but also rapid rehydration and recovery of gas-exchange following a rain event. Altogether, studies suggest that the transport physiology of seed-free vascular plants is limited relative to woody plants, but also remarkably resilient. Given their origins in the Devonian, this hardiness must explain, in part, the continued success of seed-free vascular plants, and their presence in nearly every habitat across the globe.

1 - University Of California, Integrative Biology, 1156 High Street, Santa Cruz, CA, 95064, USA
2 - California State University, Biology, 9001 Stockdale Highway, Bakersfield, CA, 93311-1022, USA
3 - Yale University, School of Forestry and Environmental Studies, Kroon Hall, 195 Prospect Street, New Haven, CT, 06511, USA
4 - Save the Redwoods League, 111 Sutter Street, 11th Floor, San Francisco, CA, 94104, USA
5 - Colgate University, Department Of Botany, 129 Ho Science Center, 13 Oak Drive, Hamilton, NY, 13346-1338, USA
6 - University of California, Ecology and Evolutionary Biology, 1156 High St., Santa Cruz, CA, 95064, USA

Keywords:
xylem
ferns
cavitation
fossil
drought.

Presentation Type: Symposium Presentation
Session: SY11, Novel approaches to plant evolution from paleontological, physiological, and developmental perspectives
Location: 101/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 4:15 PM
Number: SY11007
Abstract ID:847
Candidate for Awards:None