Density of intraspecific competitors determines the occurrence and benefits of accelerated germination

Abstract

Germination is a key process in plant recruitment and population dynamics, and seeds are expected to be under strong selection pressure to germinate under conditions that maximize subsequent plant survival. Increased rates of germination (i.e., accelerated germination) may occur in competitive environments. We examined the effects of conspecific density on the timing of germination of seeds of a bird-dispersed plant, Phytolacca americana (Phytolaccaceae, L.), in three different competitive environments. By comparing germination of seeds sown at the same time at different densities, we quantify the benefits of accelerated germination under conditions in which differences in performance among seedlings are attributable to germination timing only, and not to being sown at different times. We find that although the probability of germination is unchanged, the time to initiation of germination is significantly shorter when competition is greater. We also show that plants that germinate earlier are larger and have higher growth rates because they have more time to grow without competitors. Our work demonstrates that shifts in germination timing in response to competition can yield significant dividends for seeds that germinate earliest, but we caution that the magnitude and consequences of accelerated germination will likely depend on the competitive neighborhood.

Climatic variation and seed persistence: freeze–thaw cycles lower survival via the joint action of abiotic stress and fungal pathogens

“…These results corroborate recent studies showing that shifts towards extremes in climate variability, particularly during winter or early spring, can alter plant phenology (Inouye 2008). Shifts in seedling germination and emergence time, even for periods as short as 24 h, can alter the order in which individual seedlings access available resources and influence biomass accumulation (Ross and Harper 1972;Verdú and Traveset 2005;Orrock and Christopher 2010) and winter-mediated shifts in phenology may directly lower individual survival, productivity, Fig. 1 Effect of freeze-thaw treatment and fungicide application on a total proportion of Elymus canadensis seeds that germinated (n = 20 for each freeze-thaw and fungicide combination) and b time to emergence of E. canadensis seeds sown in field-collected soil under the four treatment combinations: constant freeze, fungicide present (n = 152), constant freeze, no fungicide (n = 117), freezethaw, fungicide present (n = 32), and freeze-thaw, no fungicide (n = 1).…”

“…Consequently, accurate predictions of climate change effects-in particular the role of climatic variability-on plant demography require a thorough understanding of how both abiotic stressors and the severity of biotic interactions will influence plant survival, recruitment potential, and the timing of critical life-history stages. Our work may have important implications beyond the population dynamics of E. canadensis, since many terrestrial plant species are limited by seed recruitment (Turnbull et al 2000), temperate plant species vary widely in their susceptibilities to fungal seed pathogens (Leishman et al 2000;Blaney and Kotanen 2001;Beckstead et al 2010), and germination timing influences individual performance, population persistence, and community composition (Dyer et al 2000;Orrock and Christopher 2010). The potential for increased seed mortality and changes in germination timing we observed in E. canadensis may be important in the context of climate change, as successful dispersal and subsequent recruitment from seeds will be required for populations of native plants to track changing climatic conditions.…”

Not only size matters: achene morphology affects time of seedling emergence in three heterocarpic species of <i>Anacyclus</i> (Anthemideae, Asteraceae)

“…It is expected that accelerated germination is selected when competition in the neighborhood is likely to be high (Orrock & Christopher, 2010). In another Asteraceae, Crepis sancta, early emergence of heavier achenes provides a competitive advantage that might have been selected to cope with sibling competition (Dubois & Cheptou, 2012).…”

Functional traits associated with plant colonizing and competitive ability influence species abundance during secondary succession: Evidence from subalpine meadows of the Qinghai–Tibetan Plateau

“…For instance, a low seed germination rate is an indicator of high seed physiological dormancy, which decreases postdispersal mortality of seeds that have been dispersed in the winter, when water availability is limited (Finch‐Savage & Leubner‐Metzger, 2006; Hu et al., 2013). However, the high nitrogen competitive environment in late succession may lead to late‐successional species having high rates of germination (i.e., accelerated germination) (Orrock & Christopher, 2010). …”