Sensitivity to high temperature and water stress in recalcitrant Baccaurea ramiflora seeds
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.
KeywordsHigh temperature stress Rainforest fragmentation Recalcitrant seeds Seed germination Species shift Water restriction
We are grateful to Prof. Richard T. Corlett in our botanical garden for his constructive comments on this study, and the National Natural Science Foundation of China (31170626) and the Chinese Academy of Sciences (CAS) 135 Program (XTBG-F03) are thanked for providing financial support for this research.
- Cao M, Zhu H, Wang H, Lan GY, Hu YH, Zhou SS, Deng XB, Cui JY (2008) Xishuangbanna tropical seasonal rainforest dynamics plot: Tree distribution maps, diameter tables and species documentation. Yunnan Science and Technology Press, KunmingGoogle Scholar
- Davies-Colley RJ, Payne GW, van Elswijk M (2000) Microclimate gradients across a forest edge. New Zeal J Ecol 24:111–121Google Scholar
- Farrant JM, Pammenter NW, Berjak P (1988) Recalcitrance: a current assessment. Seed Sci Technol 16:155–166Google Scholar
- ISTA (2006) International rules for seed testing, edition 2005. International Seed Testing Association, BasserdorfGoogle Scholar
- Laurance WF (2007) Forest destruction in tropical Asia. Curr Sci 93:1544–1550Google Scholar
- Liu WJ, Li QJ, Zhang GM, Shi JP, Bai KJ (2000) Microclimatic characteristics of canopy gaps in Shorea chinensis forest in Xishuangbanna. Acta Phytoecologica Sinica 24:356–361 (in Chinese, with English abstract) Google Scholar
- Ma YX, Liu YH, Zhang KY (1998) On microclimate edge effects of tropical rainforest fragments in Xishuangbanna. Acta Phytoecologica Sinica 22:250–255 (in Chinese, with English abstract) Google Scholar
- Roberts EH (1973) Predicting the storage life of seeds. Seed Sci Technol 1:499–514Google Scholar
- Roberts EH, King MW (1980) The characteristics of recalcitrant seeds. In: Chin HF, Roberts EH (eds) Recalcitrant crop seeds. Tropical Press SND, Kuala Lumpur, pp 1–5Google Scholar
- Wu ZY, Raven PH, Hong DY (2008) Flora of China. Science Press, Beijing (Missouri Botanical Garden Press, St. Louis) Google Scholar
- Zhu H, Wang H, Zhou SS (2010) Species diversity, floristic composition and physiognomy changes in a rainforest remnant in Southern Yunnan, China after 48 years. J Trop Forest Sci 22:49–66Google Scholar