Abstract: Plant biomass allocation pattern has important ecological and evolutionary significance for plant adaptation strategies, functional trait construction, and reproductive regeneration model. In this study, the standardized major axis (SMA) method was used to examine biomass allocation and allometric relationship of Populus euphraticaseedlings in desert riparian forest along a moisture gradient in the middle reaches of Shule River. Three plots were selected based on the distance from the river bank: near water area (plot I), medium water area (plot II) and far water area (plot III). The results showed that, with decreasing groundwater depth, the height of Populus euphratica seedling community increased (P<0.05) but the density decreased (P<0.05), and the coverage first decreased and then increased. In plot I and plot II, root-shoot ratio was greater than 1, and the increase rate of aboveground biomass was lower than that of belowground biomass. In plot III, the root-shoot ratio was close to 1, and the increase rate of aboveground and belowground biomass was almost isometric relationship. The leaf biomass fraction and root biomass fraction exhibited a decreasing trend (P<0.05), while the branch biomass fraction showed a gradually increasing trend (P<0.05), and the twig number, leaf number, crown, root length, root average diameter, root surface area and fractal dimension were significantly increased (P<0.05). The biomass allocation patterns and growth characteristics of Populus euphratica seedlings in riparian forests of Shule River reflected the environmental plasticity mechanism of plant functional traits in heterogeneous habitats, providing a theoretical basis for understanding the habitat adaptability of plants in desert riparian forest.

Key words: biomass allocation, root-shoot ratio, allometry, functional trait, desert riparian forest.