Maternal temperature during seed maturation affects seed germination and timing of bud set in seedlings of European black poplar

The maternal temperature during seed development can significantly affect seed dormancy, germination and seedling performance. While the response of germination and seedling phenology to maternal temperatures has been well studied for annuals and conifers, very few studies focus on deciduous trees. To understand the responses of seedlings to variation in maternal temperature during seed maturation, we assessed the germination, bud phenology (bud burst, bud set) and height of full sib families in a common garden. We performed three controlled crosses between three different pairs of genotypes of European black poplar (Populus nigra) to achieve full sib families in three experiments in warm (+10 °C) and cold (control) maternal environments during crossing and seed maturation. Warmer (+10 °C) maternal temperatures decreased the seed germination success. The seedlings from the warmer maternal environment also displayed later bud burst and earlier bud set, but only in one out of the three crossings (Proven ♀ x Horrues ♂). Our results indicate that the maternal environment can considerably impact on seed germination and the phenological responses of even two-year old seedlings suggesting the existence of a memory of maternal temperature during seed maturation. The seedlings resulting from the colder maternal environment grew taller than those from the warmer environment during the first, but not second, growing season. Our results further our understanding of the responses of deciduous forest trees to rapid climate change, but more research is needed to better understand the mechanisms behind the observed effects of maternal warming.