Abstract: Cryopreservation of partially dried embryonic axes represents the primary approach for long-term preservation of recalcitrant seeds. However, while many seed traits and responses relate to either pre- or post-dispersal climate, little is known about whether axis responses to cryopreservation relate to climate. For 13 Quercus species from subalpine, subtropical and temperate forests in China, we tested the hypothesis that axis responses to desiccation and cold stress co-vary and relate to climate. There were strong relationships between axis desiccation sensitivity, responses to cryopreservation and climate. Subalpine oak axes were highly desiccation-sensitive, but had high survival of freezing, even at high water contents. Temperate species were less desiccation-sensitive. However, only those from the coldest locations survived freezing when dried to lower water contents. While subtropical species had a similarly high level of desiccation-sensitivity as subalpine species, most species died under all cryo-exposure conditions. Our findings underscore the essential role of climate in shaping diverse, cold stress mitigation strategies among different Quercus groups. The paradoxical cryopreservation tolerance of highly desiccation-sensitive subalpine species, likely traits acquired during their shift to colder habitats since the mid-Miocene Himalaya-Hengduan uplift, reveals broader cold stress tolerance strategies in Quercus than previously reported, suggesting this group is suitable for long-term storage. For temperate and subtropical species, surviving cryo-exposure represented a balance between the risk of ice crystal formation and desiccation. However, the limited survival of subtropical species, many of which are threatened, highlights the need for further research to develop long-term conservation strategies.

Key words: Acorn, Chilling damage, Desiccation-sensitivity, Oak, Cold tolerance, Recalcitrant seed

摘要： Cryopreservation of partially dried embryonic axes represents the primary approach for long-term preservation of recalcitrant seeds. However, while many seed traits and responses relate to either pre- or post-dispersal climate, little is known about whether axis responses to cryopreservation relate to climate. For 13 Quercus species from subalpine, subtropical and temperate forests in China, we tested the hypothesis that axis responses to desiccation and cold stress co-vary and relate to climate. There were strong relationships between axis desiccation sensitivity, responses to cryopreservation and climate. Subalpine oak axes were highly desiccation-sensitive, but had high survival of freezing, even at high water contents. Temperate species were less desiccation-sensitive. However, only those from the coldest locations survived freezing when dried to lower water contents. While subtropical species had a similarly high level of desiccation-sensitivity as subalpine species, most species died under all cryo-exposure conditions. Our findings underscore the essential role of climate in shaping diverse, cold stress mitigation strategies among different Quercus groups. The paradoxical cryopreservation tolerance of highly desiccation-sensitive subalpine species, likely traits acquired during their shift to colder habitats since the mid-Miocene Himalaya-Hengduan uplift, reveals broader cold stress tolerance strategies in Quercus than previously reported, suggesting this group is suitable for long-term storage. For temperate and subtropical species, surviving cryo-exposure represented a balance between the risk of ice crystal formation and desiccation. However, the limited survival of subtropical species, many of which are threatened, highlights the need for further research to develop long-term conservation strategies.

关键词: Acorn, Chilling damage, Desiccation-sensitivity, Oak, Cold tolerance, Recalcitrant seed