Akhalkatsi, Maia , Abdaladze, Otar , Nakhutsrishvili, George , Smith, William K. .
Seed germination requirements in two dominant treeline species – Betula litwinowii and Rhododendron caucasicum, in the Central Caucasus.
IN the Central Greater Caucasus Mountains, Georgia, Betula litwinowii occurs on north-facing slopes, forms the alpine timberline, and reaches its treeline limit only when associated with the broadleaf evergreen shrub, Rhododendron caucasicum. We studied seed germination requirements to temperature and light at different developmental phases of seed imbibition, germination and seedling development under constant environmental conditions in both species. The germination tests at different light conditions, in the permanent darkness and day-light illumination with a photoperiod 15 h, under artificial lightening, have shown that no germination has occurred in R. caucasicum in the dark. B. litwinowii was germinated in both treatments. Germination tests at different temperature have shown that highest germination percentage occurred at room temperature in both species. The duration of phenological phases of seed imbibition, germination and seedling performance differed significantly in investigated species. Seed imbibition was prolonged in R. caucasicum (3 weeks), but germination and cotyledon formation were happened very rapidly (2 days). Seeds of B. litwinowii were already imbibed after 48 h and were germinated after 4 days. Although, cotyledon formation and seedling grows need about 2 weeks. Radicle of the birch develops root hairs soon after emergence and is very sensitive to drying. Seedlings isolated from Petri dish dry up already after 3 min. Radicle of R. caucasicum has no root hairs until first leaf develops and seedlings are more resistant to drying. They remain viable several hours in dry condition. We suppose that seed germination requirements of studied species determine their distribution patter in natural environment. R. caucasicum grows in better illuminated habitats under open subalpine krummholz and above treeline. But, it does not enter birch forest with closed canopy at lower elevations. Shaded and moist microhabitat under Rhododendron shrubs may facilitate successful establishment of birch seedlings at the treeline.
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1 - Georgian Academy of Sciences, Institute of Botany, Plant Reproduction Research, Kojori Road 1, Tbilisi, 0105, Republic of Georgia
2 - Wake Forest University, Department of Biology, PO Box 7325, 226 Winston Hall, Winston-Salem, North Carolina, 27109-7325, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 10:45 AM