Seeds of future past: climate change and the thermal memory of plant reproductive traits

Plant persistence and migration in face of climate change depends on successful reproduction by seed, a central aspectof plant life that drives population dynamics, community assembly and species distributions. Plant reproduction byseed is a chain of physiological processes, the rates of which are a function of temperature, and can be modelled usingthermal time models. Importantly, while seed reproduction responds to its instantaneous thermal environment, there isalso evidence of phenotypic plasticity in response to the thermal history experienced by the plant’s recent ancestors, bythe reproducing plant since seedling establishment, and by its seeds both before and after their release. This phenotypicplasticity enables a thermal memory of plant reproduction, which allows individuals to acclimatise to their surroundings.This review synthesises current knowledge on the thermal memory of plant reproduction by seed, and highlights itsimportance for modelling approaches based on physiological thermal time. We performed a comprehensive searchin theWeb of Scienceand analysed 533 relevant articles, of which 81 provided material for a meta-analysis of thermalmemory in reproductive functional traits based on the effect sizeZr. The articles encompassed the topics of seeddevelopment, seed yield (mass and number), seed dormancy (physiological, morphological and physical), germination,and seedling establishment. The results of the meta-analysis provide evidence for a thermal memory of seed yield,physiological dormancy and germination. Seed mass and physiological dormancy appear to be the central hubs of thismemory. We argue for integrating thermal memory into a predictive framework based on physiological time modelling.This will provide a quantitative assessment of plant reproduction, a complex system that integrates past and presentthermal inputs to achieve successful reproduction in changing environments. The effects of a warming environmenton plant reproduction cannot be reduced to a qualitative interpretation of absolute positives and negatives. Rather,these effects need to be understood in terms of changing rates and thresholds for the physiological process that underliereproduction by seed