AOBPreview originally published online on October 6, 2008
Annals of Botany 2008 102(6):953-966; doi:10.1093/aob/mcn187
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Replacement of Species Along Altitude Gradients: The Role of Branch Architecture
1 Área de Biodiversidad y Conservación, Universidad Rey Juan Carlos. c/ Tulipán s/n, E-28933 Móstoles, Madrid, Spain
2 Instituto Pirenaico de Ecología (CSIC), PO Box 202, 50080 Zaragoza, Spain
* For correspondence. E-mail ruben.milla{at}gmail.com
Received: 30 June 2008 Returned for revision: 12 August 2008 Accepted: 19 August 2008 Published electronically: 6 October 2008
Background and aims: Plant species typical of cold and warm habitats differ in a suite of morpho-physio-phenological traits, although their evolutionary routes have been poorly explored. Here, it is advocated that traits typical of different climate regimes can be largely driven by contrasting branch architectures. This is explored within Saxifraga. First, an investigation was carried out to determine whether series Ceratophyllae (lateral inflorescences) is segregated to lowlands compared with Pentadactylis (terminal inflorescences). Then, two altitudinal vicariants, S. trifurcata (lowland, with lateral inflorescences) and S. canaliculata (highland, with apical inflorescences), were selected. It was hypothesized that apical flowering of S. canaliculata constrains its growth period, bringing with it traits typical of short growth season plants, and conversely for S. trifurcata.
Methods: The hypothesis was tested by measuring plant compactness and organ pre-formation in seven populations of these species along an altitude gradient.
Key Results: Most variables differed among species. Morphological variables at all scales support that the architecture of S. canaliculata generates a more compact habit. A higher number of primordia and earlier inflorescence pre-formation in S. canaliculata indicate that it begins organogenesis earlier. Data on organogenesis suggest that the different timing of inflorescence initiation may be the origin of the contrasting architectures. Within species, shoot compactness increased, and the length of lateral primordia decreased, as altitude increased. All other metrics were similar among locations of the same species at contrasting altitudes.
Conclusions: The hypotheses linking elevational segregation of species, architecture and pheno-morphological traits were validated at broad (gen. Saxifraga) and local (altitudinal vicariants) scales. This supports the initial idea that shoot architecture may to a large extent condition high altitude adaptive syndrome.
Key words: Saxifraga, meristem activity, altitude, architecture, phenology, organogenesis
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