Seed responses to temperature indicate different germination strategies among Festuca pallescens populations from semi-arid environments in North Patagonia

Abstract

Seed germination is one of the earliest phenotypes expressed by plants, and the accuracy to germinate in the correct time and place is essential for plant population fitness. Cues that regulate germination have been exhaustively characterized in laboratory experiments. However, the way in which seed populations respond to these cues and the ecological meanings of this phenomenon are scarcely known. To help filling this gap, we studied the thermic regulation of seed germination and its link with local climatic characteristics in Festuca pallescens populations, an iconic perennial grass species of Patagonia. By coupling thermal time models with field and environmental data, we evaluated seed responsiveness to temperature during germination of nine Festuca pallescens populations distributed across their complete longitudinal range in North Patagonia. The idea behind this experimental design was to search for inter-population differences in early life traits relevant for recruitment of the species, and associate seed traits with local environmental characteristics. F. pallescens populations showed strong differences in seed sensitivity to temperature for the thermal regulation of the germination rate, described by the population mean thermal time for germination (θ(50)) and its standard deviation (σθ). The greatest values of θ(50) and σθ corresponded to populations inhabiting harsh environments. Moreover, θ(50) of the different populations showed strong correlations with their local thermal environmental parameters, indicating a relation between seed physiological traits and climate across the longitudinal gradient. We did not observe inter-population differences in the minimum temperature that allows germination (Tb = -0.47 ± 0.19 °C). Higher θ(50) and σθ in populations from harsh climates may constitute a strategy of the species to increase fitness in hostile habitats, preventing anticipated germination and promoting a slower seed bank depletion in regions where establishment is highly limited.