Positive and negative consequences of salinity stress for the growth and reproduction of the clonal plant, Iris hexagona

Authors

  • Peter A. Van Zandt,

    Corresponding author
    1. Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana 70504–2451, USA, and
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  • Mark A. Tobler,

    1. Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana 70504–2451, USA, and
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    • *

      Present address: Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana 70118, USA.

  • Edmund Mouton,

    1. Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana 70504–2451, USA, and
    2. Louisiana Department of Wildlife and Fisheries, 2415 Darnall Road, New Iberia, Louisiana 70560, USA.
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  • Karl H. Hasenstein,

    1. Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana 70504–2451, USA, and
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  • Susan Mopper

    1. Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana 70504–2451, USA, and
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Present address and correspondence: P. A. Van Zandt, Washington University, Department of Biology, 1 Brookings, Campus Box 1137, St Louis, MO 63130, USA (e-mail vanzandt@biology2.wustl.edu).

Summary

  • 1Salinization is a growing environmental stress in wetland ecosystems world-wide. Several models have been proposed that predict clonal plant responses to stress, including that environmental stress stimulates sexual reproduction.
  • 2We conducted a common-garden experiment to investigate the effects of salinity on 10 natural populations of Iris hexagona, a clonal perennial endemic to freshwater and brackish wetlands of the North American Gulf Coast.
  • 3Salinity reduced vegetative growth but either increased or had neutral effects on sexual reproduction, consistent with the clonal stress hypothesis. Salinity of 4 µg g−1 more than doubled the number of seeds produced compared with freshwater controls, but flower number and seed mass were unaffected.
  • 4Salinity reduced total below-ground mass by nearly 50% compared with controls, with no significant change in rhizome numbers.
  • 5Plants from 10 randomly selected I. hexagona populations differed dramatically in growth and reproduction, independent of salinity. Total biomass that accumulated over the 20-month experiment ranged across all treatments from 52 to 892 g, and flower numbers varied from 2.3 to 11.3 per replicate.
  • 6Populations did not respond differently to salinity, except with respect to above- : below-ground ratios, thus providing no conclusive evidence for local adaptation to salinity stress.
  • 7Our results concur with published models of plant reproductive strategies in variable environments, in that environmental stress stimulated sexual reproduction at the expense of growth. However, these models do not predict the observed sharp decline in seed production at near lethal salinity levels.

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