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Jumping Seed Storage Types: Effect of Developmental Heat Sum at Continental Scales on the Seed Desiccation Tolerance Trait

Seeds of Acer pseudoplatanus ‘jump’ desiccation tolerance ‘types’ as harvests are made from the introduced (bottom) to native ranges (top)

This project is one of a series in the theme 'Climate and Reproductive Biology'.

The parental environment during seed development, in particular air temperature, can impact on seed mass, germinability and dormancy. However, whilst inter-seasonal or inter-site differences in seed lot response to desiccation and in seed physical traits have been recorded in some recalcitrant seeded species a relationship to measured environmental conditions has not been explored.

During development, orthodox seeds pass through three distinct phases: embryogenesis, active biosynthesis of reserve material leading to a rapid increase in seed fresh and dry weight, and seed maturation when dry weight accumulation ceases and fresh weight declines markedly (in dry dehiscent fruit types) or remains relatively constant (in fleshy fruit types). The transition from the second to the third phase coincides approximately with the acquisition of desiccation tolerance and physiological evidence suggests that seeds of many recalcitrant species do not complete the second phase of development before fruit abscission.

Thus, we hypothesized that air temperature may affect the rate of seed development and affect the relative position of a seed lot within phase II or potentially phase III of development. We have assessed this proposition using seed lots of two recalcitrant seeded tree species that occur widely in Europe (Aesculus hippocastanum and Acer pseudoplatanus) collected from sites of differing summer temperatures (from Norway to Greece). These two species were chosen because Aesculus hippocastanum is fully recalcitrant in its seed behaviour while Acer pseudoplatanus has been described as minimally recalcitrant i.e. it may be “closer” to phase III of development at the time of seed shed.

We have found for both species that seed developmental status at the point of natural dispersal is strongly related to air temperatures (heat sum) during development, with seed lots from warmer locations being more mature as assessed by physical and physiological traits. Furthermore, at least for Acer pseudoplatanus, more developed seed lots “jumped” from the recalcitrant seed storage category to the intermediate category indicating that there may be some potential for conventional genebank storage of this species.

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