Abstract: Biomass allocation pattern affects the gaining recources and competition ability of plant. Elucidation of the biomass allocation patterns among different root branch orders is important for understanding the phenotypic plasticity of plants under different habitats. In this study, we aimed to study the biomass allocation patterns of the first three root branch orders for Reaumuria soongorica in response to slope aspect change in a desert grassland on the northern slope of Qilian Mountains, Northwest China with the method of whole root system excavation and with ArcGIS to construct the digital elevation model for the study sites. The results showed that the coverage, density, height, species richness, aboveground biomass and soil moisture content of the plant community exhibited different variation tendencies in different slope aspects (P<0.05). The change patterns among the density, height, rootshoot ratio of R. soongorica varied with slope aspects (P<0.05). With the slope aspect turning from south to west, east and north, the proportion of the firstorder branch biomass of R. soongorica gradually increased (P<0.05), while the proportion of the secondorder and thirdorder branch biomass decreased (P<0.05). An isometric relationship was found between secondorder branch biomass and thirdorder branch biomass in plots within each slope, whereas the growth speed of firstorder branch biomass was greater than that of secondorder and thirdorder branch biomass. The root resource allocation mode by reasonable tradeoff among different branch orders with changes in slope aspect of the habitat reflected the adaptation mechanism of plant populations to environment under conditions of multiple competition for resources.

Key words: fuel, drying coefficient, moisture content, wind speed