Different responses of two contrasting Populus davidiana populations to exogenous abscisic acid application

Purpose of this study was to investigate different responses of two contrasting Populus davidiana populations to exogenous abscisic acid (ABA) application under well-watered and water-stressed conditions, and to further elucidate the role of ABA in drought tolerance. Two contrasting populations were from the wet and dry climate regions in China, respectively. Exogenous ABA was applied to the leaves by spraying and changes in plant growth and structure, gas exchange, endogenous ABA concentration and water use efficiency were monitored. 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) and transpiration (E), and significantly increased root/shoot ratio (Rs), transpiration efficiency (WUET), instantaneous water use efficiency (WUEI) and carbon isotope composition (delta(13)C) under well-watered and water-stressed conditions. These morphological and physiological responses to exogenous ABA application showed that ABA could play an important role to control drought tolerance in P davidiana populations. However, distinct population differences were found in ABA-induced growth reduction, gas exchange decrease and water use efficiency increase. Compared with the wet climate population, the dry climate population was more responsive to exogenous ABA application, resulting in lower Ht, Tb, La, Sla, A and E, and higher Rs, WUET, WUEi and delta(13)C under all experimental treatments. Our results provide strong evidence for adaptive differentiation between populations of P. davidiana. (C) 2003 Elsevier B.V. All rights reserved.