Effects of litter and standing biomass on growth and reproduction of two annual species in a Mediterranean old-field

Authors

  • CYRILLE VIOLLE,

    1. Centre d’Ecologie Fonctionnelle et Evolutive (UMR 5175), 1919, Route de Mende, 34293 Montpellier Cedex 5, France, and
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  • JEAN RICHARTE,

    1. Centre d’Ecologie Fonctionnelle et Evolutive (UMR 5175), 1919, Route de Mende, 34293 Montpellier Cedex 5, France, and
    2. E.N.S.A.-M., Département ‘Sciences pour la Protection des Plantes et Ecologie’, 2 Place Viala, 34060 Montpellier Cedex 1, France
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  • MARIE-LAURE NAVAS

    1. Centre d’Ecologie Fonctionnelle et Evolutive (UMR 5175), 1919, Route de Mende, 34293 Montpellier Cedex 5, France, and
    2. E.N.S.A.-M., Département ‘Sciences pour la Protection des Plantes et Ecologie’, 2 Place Viala, 34060 Montpellier Cedex 1, France
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Author for correspondence: Cyrille Violle (e-mail cyrille.violle@cefe.cnrs.fr).

Summary

  • 1We tested the hypothesis that the competitive ability of a plant changes during its lifetime, by evaluating variations in the relative influence of standing biomass and litter on plant performance.
  • 2Seedlings of two annual herbaceous species (‘targets’), of contrasted life-forms (Crepis foetida and Bromus madritensis) were transplanted into an old-field. The competitive ability of seedlings, vegetative and reproductive plants towards neighbours was recorded over one growing season.
  • 3Fourteen traits related to plant morphology, growth and reproduction were measured to assess the competitive ability of targets. Relationships among traits were characterized to identify a set of traits as a surrogate of target competitive ability.
  • 4The two target species responded similarly. Early growth was facilitated by litter and, to a greater degree, by vegetative biomass. Thereafter, the effect of neighbouring vegetation on target performance was negative, with a maximum depressing effect on reproduction (especially seed number and date of flowering) despite a weak facilitative effect of litter. Plant basal diameter, measured at peak growth period, and total number of inflorescences per plant, were found to predict growth and reproductive components of competitive ability, respectively.
  • 5Assessing the effects of competition for population success from the response of vegetative plants will underestimate its importance because competition appears to exert its maximal impact on seed production.

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