Germination response to various temperature regimes of four Mediterranean seeder shrubs across a range of altitudes
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Germination response to various temperature regimes of four Mediterranean seeder shrubs across a range of altitudes Daniel Chamorro • Bele´n Luna • Jose´ M. Moreno
Received: 24 June 2013 / Accepted: 26 September 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract In dry-summer seasonal climates, the beginning of the rainy season can prompt germination under different temperatures, depending on altitude. Understanding germination responses to temperature with altitude is important in fire-prone environments for species regenerating after fire from seeds (seeders), particularly under changing climate. Here we investigated the role of temperature in four Mediterranean seeder shrubs from Central Spain. Seeds from 17 sites (285–1,253 m altitude), of two hard-seeded nanophanerophytes (Cistus ladanifer and C. salviifolius) and two soft-seeded chamaephytes (Lavandula pedunculata and Thymus mastichina) were investigated. Intact and heat shock treated seeds were set to germinate under four temperature regimes, including a treatment simulating future warming. GLM with binomial or gamma functions were used to test treatment effects using altitude as a covariate. Altitude was a significant covariate only in L. pedunculata. Temperature did not affect final germination in either Cistus, but it significantly affected T. mastichina, and interacted with
D. Chamorro B. Luna J. M. Moreno (&) Departamento de Ciencias Ambientales, Universidad de Castilla-La Mancha, Av. Carlos III s/n, 45071 Toledo, Spain e-mail: [email protected] D. Chamorro e-mail: [email protected] B. Luna e-mail: [email protected]
altitude in L. pedunculata, whereby the higher the altitude the less it germinated with decreasing temperature. Germination speed (T50) was lower at colder temperatures in all but C. salviifolius that was insensitive to our treatments. Heat shock significantly increased final germination in both Cistus and T. mastichina, but did not interact with temperature or altitude. We conclude that germination response to temperature, including varying sensitivity with altitude, differed among these species; thus, changes in the timing of the onset of the rainy season will diversely affect populations at various altitudes. We discuss our results in a context of changing climate and fire. Keywords Elevation gradient Global warming Niche breadth Physical dormancy Species range
Introduction Temperature is perhaps the most important environmental factor controlling germination of imbibed seeds (Baskin and Baskin 1998; Probert 2000). Temperature and other environmental factors affecting germination vary along the distribution range of a species, and variations in germination responses along gradients of temperature or other factors have been documented (Meyer and Allen 1999; Donohue 2002). In seasonal climates with a dry and warm period, like
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Mediterranean-type areas, germination proceeds once suitable moisture conditions occur, most commonly following autumn rains and until spring (Keeley 1991; Espi
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