Physiology and morphology of Pinus sylvestris seedlings from diverse sources under cyclic drought stress

We examined seed source variation in drought tolerance characteristics of Pinus sylvestris seedlings from 12 diverse geographic origins representing a longitudinal transect across the species range. The seedlings were subjected to three dry-down cycles in raised water-use efficiency in a greenhouse experiment. We measured pre-dawn needle water potential (Psi (n)) and instantaneous water-use efficiency (WUE) (W) during the cyclic droughts. Seedling survival, growth, biomass allocation to roots, and carbon isotope ratio (delta C-13) were measured at the end of the experiment. The seed sources varied (P < 0.05) in biomass growth, biomass allocation to roots, and delta C-13. In general, seedlings from the drier central Asian seed sources survived longer under drought than seedlings from more mesic European and coastal seed sources. Seedlings from the Asian seed sources were smaller, allocated more biomass to roots, and had higher integrative water-use efficiency (as indicated by higher delta C-13) than the seedlings from the European sources. Seed source variation in P. and W was not significant (P > 0.05). Carbon isotope ratio was correlated with precipitation at the seed origin (r = -0.75, P < 0.05). The results of this study support the generalization that Scots pine seed sources from the interior portion of the species range grow slower but are more drought tolerant than European seed sources. (C) 2001 Elsevier Science B.V. All rights reserved.