This study aims to investigate the effects of water stress on the growth, biomass allocation, and physiological characteristics of seedlings of three afforestation tree species, in order to screen for species with strong drought resistance and to provide a scientific basis for water-saving and drought-resistant afforestation in arid areas.

Two-year-old seedlings of Elaeagnus angustifolia, Populus euphratica, and Xanthoceras sorbifolium were subjected to four water treatments: 75%-80% of field capacity (CK), 60%-65% of field capacity (T1), 45%-50% of field capacity (T2), and 30%-35% of field capacity (T3). Seedling growth, physiological and biochemical indices, and biomass allocation patterns under water stress were systematically measured, and the differences in the responses of the seedlings of each tree species to water stress were analyzed.

1) With increasing water stress, the increments in height and ground diameter of the three tree species seedlings generally decreased. Among them, E. angustifolia seedlings exhibited the largest increments in height and ground diameter across all water treatments, and the three species showed the smallest reductions in height and ground diameter growth under the T1 treatment; 2) As water stress intensified, the root, stem, and leaf biomass of the three tree species seedlings significantly decreased, while the root-to-shoot ratio (R/S) significantly increased. Among them, X. sorbifolium seedlings exhibited the greatest increase in R/S, whereas E. angustifolia seedlings accumulated the highest root, stem, and leaf biomass across all treatments; 3) With increasing water stress, chlorophyll content and value of photosynthetic parameters such as net photosynthetic rate (Pn) and stomatal conductance (Gs) significantly decreased (P<0.05). Notably, P. euphratica seedlings had significantly higher valuse of Pn, Gs, and other photosynthetic parameters than the other two species (P<0.05), while the water use efficiency (WUE) of E. angustifolia seedlings was significantly higher than those of the other two species under the T3 treatment (P<0.05); 4) As water stress intensified, the malondialdehyde (MDA) content, osmoregulatory substance content, and the activities of superoxide dismutase (SOD) and peroxidase (POD) generally increased across the three species. Among them, E. angustifolia seedlings exhibited relatively higher chlorophyll content, osmoregulatory substance contents, and POD activity, while X. sorbifolium seedlings showed relatively higher MDA content.

Under water stress, the growth of the three tree species seedlings was inhibited to varying degrees, with multiple photosynthetic indices significantly decreasing and stress-resistant physiological indices showing an increasing trend. However, the three species were ranked in drought resistance as follows. Based on the comprehensive evaluation results using the membership function method, the drought resistance of the three tree species seedlings ranked as follows: E. angustifolia showed the strongest resistance, followed by P. euphratica, and X. sorbifolium showed the weakest resistance.