Cool Temperatures and Post-Germination Adaptations Enhance Seedling Recruitment in the Subalpine Oak Quercus longispica (Fagaceae)

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Abstract
Quercus longispica is a dominant shrub in the Himalayan subalpine region, demonstrating high levels of persistence despite high seed predation and extreme climatic conditions. However, its seed germination ecology and adaptations for seedling recruitment remain poorly understood. This study investigated the effects of temperature, water potential, and insect damage on seed germination and seedling establishment. Pre-germination seed traits and seed-to-seedling ontogeny were systematically analyzed. Our results demonstrated that seed germination percentages decreased with increasing insect damage across all temperature and water potential treatments. Cool temperatures (5–10 °C) yielded the highest germination percentages, potentially due to the suppression of parasitoid activity and mildew growth. While drought conditions also suppressed parasitoid activity, they significantly increased seed mortality. Despite a decline in seedling performance with increasing seed damage, overall seedling establishment remained robust. Several adaptive traits enable Q. longispica to persist in its harsh environment. Multi-seeded, non-apical embryos combined with rapid germination help embryos evade or escape damage from parasitism and predation. The rapid elongation of cotyledonary petioles pushes the embryo axis into the soil, with rapid nutrient and water transfer from the cotyledon to the taproot, thereby avoiding the threats of predation, drought, cold, and wildfire. Additionally, temperature-regulated epicotyl dormancy at the post-germination stage prevents the emergence of cold-intolerant seedlings in winter. This study provides the first comprehensive description of seed-to-seedling ontogeny in this Himalayan subalpine oak, offering crucial insights into the adaptive mechanisms that facilitate successful seedling recruitment in the challenging subalpine habitats.
Funding Information
  • National Natural Science Foundation of China (32460060, 31972858, 2023YFF1305000, KFJJ21-05, Y4ZK111B04, 2023Y0214)
  • National Key Research and Development Program of China (32460060, 31972858, 2023YFF1305000, KFJJ21-05, Y4ZK111B04, 2023Y0214)
  • Fund of Key Laboratory for Silviculture and Forest Resources Development of Yunnan Province, Yunnan Academy of Forestry and Grassland (32460060, 31972858, 2023YFF1305000, KFJJ21-05, Y4ZK111B04, 2023Y0214)
  • Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences (32460060, 31972858, 2023YFF1305000, KFJJ21-05, Y4ZK111B04, 2023Y0214)
  • Yunnan Provincial Department of Education (32460060, 31972858, 2023YFF1305000, KFJJ21-05, Y4ZK111B04, 2023Y0214)

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