Population differences in physiological and morphological adaptations of Populus davidiana seedlings in response to progressive drought stress

Abstract

Population differences in dry matter accumulation and allocation, gas exchange, abscisic acid content and water use efficiency of Populus davidiana seedlings were measured after exposure to well-watered and progressive drought stress treatments. Three populations used were form dry, middle and wet climate regions, respectively. Significant differences in height growth (Ht), total biomass (Tb), total leaf area (La), root/shoot ratio (Rs), specific leaf area (Sla), net photosynthesis ( A), transpiration ( E) and instantaneous water use efficiency (WUE i) between the populations were detected under two watering regimes; population differences in abscisic acid content (ABA) and carbon isotope composition ( δ 13 C ) were also detected under progressive drought stress treatment, but these differences were not significant under well-watered treatment. Compared with the wet climate population, the dry climate population had lower Ht, Tb, La, Sla, A and E, and higher Rs and WUE i. On the other hand, the dry climate population also exhibited higher ABA and δ 13 C as effected by drought stress than the wet climate population. These morphological and physiological adaptations to water availability showed that the different populations may employ different survival strategies under drought stress at the initial phase of seedling growth and establishment. The wet climate population possesses a prodigal water use strategy and quick growth, while the dry climate population exhibits a conservative water use strategies and slow growth. These differences in drought responses may be used as criteria for genotype selection in different climate regions.