Variation in the seasonal germination niche across an elevational gradient: the role of germination cueing in current and future climates

Abstract

Premise The timing of germination has profound impacts on fitness, population dynamics, and species ranges. Many plants have evolved responses to seasonal environmental cues to time germination with favorable conditions; these responses interact with temporal variation in local climate to drive the seasonal climate niche and may reflect local adaptation. Here, we examined germination responses to temperature cues in Streptanthus tortuosus populations across an elevational gradient. Methods Using common garden experiments, we evaluated differences among populations in response to cold stratification (chilling) and germination temperature and related them to observed germination phenology in the field. We then explored how these responses relate to past climate at each site and the implications of those patterns under future climate change. Results Populations from high elevations had stronger stratification requirements for germination and narrower temperature ranges for germination without stratification. Differences in germination responses corresponded with elevation and variability in seasonal temperature and precipitation across populations. Further, they corresponded with germination phenology in the field; low‐elevation populations germinated in the fall without chilling, whereas high‐elevation populations germinated after winter chilling and snowmelt in spring and summer. Climate‐change forecasts indicate increasing temperatures and decreasing snowpack, which will likely alter germination cues and timing, particularly for high‐elevation populations. Conclusions The seasonal germination niche for S. tortuosus is highly influenced by temperature and varies across the elevational gradient. Climate change will likely affect germination timing, which may cascade to influence trait expression, fitness, and population persistence.

Physiological and environmental control of seed germination timing in Mediterranean mountain populations of Gundelia tournefortii

“…However, it should be considered that this plant can be found also at low altitudes (Hind 2013). Thus, it is possible that this species could show phenotypic plasticity to temperature and vary its seasonal germination niche across populations, as previously reported along an altitudinal cline for other Mediterranean plants, such as Streptanthus tortuosus in California (Gremer et al 2020). Therefore, considering that this study only focused on mountain poulations of this species at altitudes comprised between 1181 and 1672 m a.s.l., further studies should be carried out to understand the intraspecific genetic and ecological variability of this species, covering the whole altitudinal gradient, as well as different geographic regions, of the species distribution.…”

Water the odds? Spring rainfall and emergence‐related seed traits drive plant recruitment

“…If combined physical constraints and light sensitivity both contribute to emergence limitation for small‐seeded species (even under 1.5 cm of soil, as in our study; Sonkoly et al 2020), then managing recruitment will require dual consideration of small‐scale seed microclimate factors alongside larger‐scale climatic drivers, like drought. Independently, higher levels of dormancy were also associated with lower emergence across species – a mechanism which could also be impactful within species (Gremer et al 2020). Although it appears obvious that more dormant seeds emerge less in the first year, seed physiology traits remain under‐utilized in trait‐based predictive frameworks (Jimenez‐Alfaro et al 2016) and deserve greater attention in the context of anticipating both short‐ and long‐term community reassembly and restoration outcomes (Barak et al 2018, Kildisheva et al 2019).…”

Modes of climate variability bridge proximate and evolutionary mechanisms of masting

“…These changes are impacting-and will further impact in the near future-the associated ecological processes and their multiple spatio-temporal synergies [33,128], including masting [30]. In cases where weather influencing proximate mechanisms anticipates weather during germination or seedling development, it is likely that these processes will become decoupled as climates change [129]. Where lags in ecosystem processes result in environmental prediction, it is possible that those processes may remain coupled even as Earth's climate systems change considerably.…”