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Keywords:

  • 13C;
  • carbon isotope discrimination;
  • competition;
  • nitrogen;
  • root distribution;
  • species composition

Summary

  • 1
     Interspecific and temporal variations in presumed water-use efficiency, as measured by carbon isotope discrimination (Δ), were examined in a Greek semiarid herbaceous grassland, and the hypothesis tested that competition for water is a factor in determining vegetation structure.
  • 2
     Experiments were conducted for 3 years in an upland grassland consisting of exclusively C3 perennial species. The most abundant species were the grasses Poa pratensis L., Lolium perenne L. and Festuca valida (Uechtr.) Penzes; the forbs Achillea millefolium L., Plantago lanceolata L. and Taraxacum officinale Weber ex Wigg; and the legume Trifolium repens L.
  • 3
     Rooting depth did not explain plant Δ in this shallow-soil site, where soil moisture was concentrated in the top of the profile.
  • 4
     Although temporal variation for Δ was significant within most species, changes in ranking of species were slight throughout three growing seasons.
  • 5
     Δ Was negatively related to species biomass production, which means that species’ abundances were positively related to species’ water-use efficiencies. Δ Was positively related to leaf N content, which we interpret as an autocorrelation with water availability.
  • 6
     The results of this study are consistent with the notion that, in an environment where water is scarce, plants may compete effectively by increasing their potential water-use efficiency as measured by Δ, and that species abundance is regulated by competition-driven water depletion.