Intra‐specific variation and climate differentially shape the thermal germination niches of three co‐occurring woodland forbs

Abstract

AbstractUnderstanding plant responses to temperature is critical for predicting their vulnerability to global warming and for planning management responses. Germination is a key life‐stage, strongly regulated by temperature, that affects the potential for plant populations to persist. Here, we compared the thermal germination niches of three unrelated, declining woodland forb species – Arthropodium fimbriatum (Asparagaceae), Bulbine bulbosa (Asphodelaceae), Microseris walteri (Asteraceae) – across common temperature and precipitation gradients, to characterize the relationships with home‐site climate, and associated implications for ecological restoration in a changing climate. Open‐pollinated seed were sampled from 14–15 populations per species across an aridity gradient in south‐eastern Australia. Germination responses for each population were tested in controlled temperature cabinets under five temperature regimes encompassing contemporary and projected future temperatures. Optimum germination temperature and thermal germination niche were characterized and assessed for associations with home‐site climate and potential germination under projected climate change. The three species showed significant intra‐specific variation in the thermal germination niche. Optimum germination temperature was correlated with home‐site climate, suggesting adaptive variation among populations in germination requirements. However, the pattern of variation in optimum germination across the environmental gradients was not always consistent among the species. Future temperatures projected under climate change tended to be outside the current thermal germination niche for all species, indicating potential benefits of incorporating pre‐adapted populations in ecological restoration. Climate‐related intra‐specific variation in the thermal germination niche provides evidence for local adaptation to climate in all three forb species and suggests potential differences among populations in vulnerability to global warming. These results emphasize the importance of understanding the extent of intra‐specific variation in key life history traits to better manage and conserve populations and restore their ecosystems as climates change.