Morphological and physiological responses of two contrasting Poplar species to drought stress and exogenous abscisic acid application

Purpose of this study was to investigate different morphological and physiological responses of two species of Sect. Tacamahaca Spach, Populus kangdingensis C. Wang et Tung (P. kangdingensis) and Populus cathayana Rehder (P cathayana), to exogenous abscisic acid (ABA) application under well-watered and water-stressed conditions and to further elucidate the role of ABA in drought tolerance. P. kangdingensis and P. cathayana possess different natural habitats in the eastern Himalaya; the first one occurs at high-altitude zone and the second one at low-altitude zone. Exogenous ABA was applied to the leaves by spraying, changes in plant growth and structure, gas exchange, endogenous ABA content and carbon isotope composition (delta(13)C) were measured. The results demonstrated that exogenous ABA application significantly decreased height growth (Ht), total biomass (Tb), total leaf area (La), specific leaf area (Sla), net photosynthesis (A), transpiration (E) and stomatal conductance (g) and significantly increased root/shoot ratio (Rs), fine root/total root ratio (Ft) and delta(13)C under well-watered and water-stressed conditions. However, distinct interspecific differences were found in ABA-induced growth reduction, gas exchange decrease and delta(13)C increase. P. kangdingensis was more responsive to applied ABA than P. cathayana, resulting in larger decreases in Ht, Tb, La, E and g, and larger increases in Rs and ABA. In addition, P. kangdingensis also exhibited higher Ft and delta(13)C than P. cathayana under all experimental treatments. Our results provide strong evidence for adaptive differentiation between two contrasting poplar species in the eastern Himalaya. (C) 2004 Elsevier Ireland Ltd. All rights reserved.