title: Sensitivity to high temperature and water stress in recalcitrant Baccaurea ramiflora seeds.
abstract: Southeast Asia experiences one of the highest rates of deforestation in the tropics due to agricultural expansion, logging, habitat fragmentation and urbanization. As tropical rainforests harbour abundant recalcitrant-seeded species, it is important to understand how recalcitrant seeds respond to deforestation and fragmentation. Baccaurea ramiflora is a recalcitrant-seeded species, widely distributed in Southeast Asian tropical rainforest. In this study, B. ramiflora seeds were sown in three plots, one in a nature reserve and two in disturbed holy hill forests, to investigate seed germination and seedling establishment in the field, while laboratory experiments were conducted to investigate the effects of high temperature and water stress on germination. It was found that seed germination and seedling establishment in B. ramiflora were clearly reduced in holy hills compared to the nature reserve, although the seeds were only moderately to minimally recalcitrant. This was potentially caused by increased temperature and decreased moisture in holy hills, for laboratory experiments showed that seed germination was greatly inhibited by temperatures ≥35 °C or water potentials ≤-0.5 MPa, and depressed by heat treatment at 40 °C when the continuous heating period lasted for 240 h or daily periodic heating exceeded 10 h. Unlike orthodox seeds, which can endure much higher temperatures in the air-dried state than in the imbibed state, both blotted and immersed B. ramiflora seeds lost viability within a narrow temperature range between 50 and 60 °C. As recalcitrant seeds can be neither air-dried nor heated, species producing recalcitrant seeds will suffer more than those producing orthodox seeds in germination and seedling establishment from increased temperature and decreased moisture in fragmented rainforests, which results in sensitivity of recalcitrant-seeded species to rainforest fragmentation.
authors.affiliation: Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, 666303, Yunnan, China. wenb@xtbg.org.cn.
authors.forename: Bin
authors.initials: B
authors.lastname: Wen
authors.affiliation: Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, 666303, Yunnan, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Minghang
authors.initials: M
authors.lastname: Liu
authors.affiliation: Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, 666303, Yunnan, China.
authors.forename: Yunhong
authors.initials: Y
authors.lastname: Tan
authors.affiliation: Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, 666303, Yunnan, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Liu
mesh_terms: D000222:Adaptation, Physiological; D003681:Dehydration; D003890:Desiccation; D018525:Germination; D006358:Hot Temperature; D006813:Humidity; D019684:Magnoliopsida / Q000502:physiology*; D065947:Rainforest; D036226:Seedlings / Q000502:physiology; D012639:Seeds / Q000502:physiology*; D013312:Stress, Physiological; D014022:Tissue Survival; D014867:Water
chemical_list: D014867:Water
keywords: High temperature stress; Rainforest fragmentation; Recalcitrant seeds; Seed germination; Species shift; Water restriction