Seed traits and climate resilience in three Mesua species from Sri Lanka

Abstract

To test the hypothesis that variations of seed traits are adaptations to their habitat conditions and to evaluate adaptability of species to climate change, we investigated variation in seed traits in three Mesua species from Sri Lanka. Seed traits of the dominant native tree M. ferrea sampled across a wide climatic range were compared to those of sub-dominant M. thwaitesii and critically restricted M. stylosa. Seed shape, size, mass, moisture content, seed coat ratio and germinability were studied. Seed storage behavior was evaluated using the hundred seed method and two predictive models: TSW-MC (Thousand seed weight – Moisture content) and SCR-SM (Seed Coat Ratio – Seed Mass). Mesua stylosa had larger seeds with higher MC than the other two species, which allow it to produce seedlings with high tolerance to harsh conditions. Further, M. stylosa seeds are dormant and desiccation sensitive in contrast to those of M. thwaitesii and M. ferrea, whose seeds are non-dormant and desiccation tolerant. These seed traits make M. stylosa seeds more adapted to its unique habitat (freshwater swamp forest in the wet zone), proving our hypothesis that seed trait variations are adaptations to environmental variability in the species’ habitats. Inter-population variation was observed in M. ferrea based on seed mass, MC and SCR. However, inter-annual variation was only observed in MC. When the seed traits were considered, M. ferrea and M. thwaitesii exhibit climate resilience aligned with more dry conditions predicted under climate change with low climate resilience in M. stylosa being desiccation sensitive and dormant.