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Thermal thresholds for seed germination in Mediterranean species are higher in mountain compared with lowland areas

Published online by Cambridge University Press:  11 December 2018

Rosangela Picciau*
Affiliation:
Centro Conservazione Biodiversità, Dipartimento di Scienze della Vita e dell'Ambiente, Università degli Studi di Cagliari, Viale S. Ignazio da Laconi, 11–13, 09123, Cagliari, Italy Banca del Germoplasma della Sardegna (BG-SAR), Hortus Botanicus Karalitanus (HBK), Università degli Studi di Cagliari, Viale Sant'Ignazio da Laconi, 9–11, 09123, Cagliari, Italy
Hugh W. Pritchard
Affiliation:
Royal Botanic Gardens, Kew, Wellcome Trust Millennium Building, Wakehurst Place, Ardingly, West Sussex RH17 6TN, UK
Efisio Mattana
Affiliation:
Centro Conservazione Biodiversità, Dipartimento di Scienze della Vita e dell'Ambiente, Università degli Studi di Cagliari, Viale S. Ignazio da Laconi, 11–13, 09123, Cagliari, Italy Royal Botanic Gardens, Kew, Wellcome Trust Millennium Building, Wakehurst Place, Ardingly, West Sussex RH17 6TN, UK
Gianluigi Bacchetta
Affiliation:
Centro Conservazione Biodiversità, Dipartimento di Scienze della Vita e dell'Ambiente, Università degli Studi di Cagliari, Viale S. Ignazio da Laconi, 11–13, 09123, Cagliari, Italy Banca del Germoplasma della Sardegna (BG-SAR), Hortus Botanicus Karalitanus (HBK), Università degli Studi di Cagliari, Viale Sant'Ignazio da Laconi, 9–11, 09123, Cagliari, Italy
*
Author for correspondence: Rosangela Picciau, Email: rosangela.picciau@gmail.com

Abstract

Each taxon is characterized by a temperature range over which seed germination is possible and this may vary in space and time in relation to climate and ecological conditions. We used thermal modelling to test the hypothesis that thermal thresholds for seed germination can predict germination timing of Mediterranean species along an altitudinal and environmental gradient. Seeds of 18 species were collected in Sardinia from sea level to 1810 m above sea level, and germination tests were carried out at a range of constant (5 to 25°C) and alternating (25/10°C) temperatures. Different dormancy-breaking treatments [gibberellic acid (GA3), cold (C) and warm (W) stratifications and dry after ripening (DAR)] were applied. The annual pattern of soil temperatures was recorded using 24 data-loggers buried close to the study species. The logged soil temperatures distinguished ‘Mediterranean lowland’ from ‘Mediterranean mountain’ species. Although germination was >50% in untreated seeds of most species, GA3 had a positive effect in all species. C either inhibited or had a neutral effect on germination, W did not enhanced seed germination, while DAR had a positive effect only in species from coastal environments. The thermal time constant (S) for 50% germination ranged from 22 to 357°Cd (degree days) above base temperatures (Tb) of –9 to 9°C, depending on species and treatments. Mediterranean lowland species had lower Tb values compared with upland species. This study revealed significant differences in germination thresholds of Mediterranean lowland and mountain species in relation to Tb and S that probably have an impact on germination timing in the field and niche competitiveness.

Information

Type
Research Paper
Copyright
Copyright © Cambridge University Press 2018 

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