Germination response to various temperature regimes of four Mediterranean seeder shrubs across a range of altitudes

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 altitude in L. pedunculata, whereby the higher the altitude the less it germinated with decreasing temperature. Germination speed (T 50) 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.

Intra-population level variation in thresholds for physical dormancy-breaking temperature

“…Germination rates varied significantly among individuals in our study, a strategy maintained by species as a form of temporal bet-hedging (Venable, 1989;Fenner and Thompson, 2005;Wang et al, 2009). Differences in germination rate spread germination over time, ensuring that some seeds can respond quickly to a rainfall event after dormancy has broken, while others require longer to initiate germination and therefore enable maintenance of a seed bank that can respond to subsequent rainfall events, even if the initial cohort has failed (Aŕan et al, 2013;Chamorro et al, 2013). While all individuals of some study species, such as D. floribunda and A. ericoides, showed similar patterns of higher germination at higher temperature treatments, variation in germination rates among individuals were maintained.…”

Assessing Bacterial Diversity in the Rhizosphere of Thymus zygis Growing in the Sierra Nevada National Park (Spain) through Culture-Dependent and Independent Approaches

“…However, although some progress is being made, the rhizosphere of non-cultivated plant species remains largely unknown [ 5 ]. Members of the genera Thymus constitute aromatic plants typical of Mediterranean shrublands which may participate in vegetation succession [ 8 ] and as seeders for re-vegetation after forest fires [ 9 ]. In addition, the essential oils and volatile compounds derived from thyme species are valuable for the pharmaceutical, food and perfume industries due to their medicinal, anti-oxidant, fragrance and culinary properties.…”

Use of Restoration Plantings to Enhance Bird Seed Dispersal at the Roadside: Failures and Prospects

“…All seeds were identified using an ad hoc catalogue of seeds collected from the embankments and their surrounding matrices. The viability of seeds was estimated by means of germination tests in peat at 15% RH and 22 °C, under a 12 h light photoperiod for 12 months (Chamorro et al 2013). We also measured the abundance of plants with fleshy fruits in surrounding matrices to test the effect of fruit availability on frugivorous birds.…”