Abstract: Tradeoff is the basis of life history strategy theory. Elucidation of the tradeoff between root forks and link length is important for understanding the phenotypic plasticity of plants under different habitat conditions. By using the ArcGISestablished regional digital elevation model (DEM), this paper studied the tradeoff relationship between root forks and link length of Reaumuria soongorica at different slope aspects in a desert grassland on the northern slope of Qilian Mountains, Northwest China with the method of whole root system excavation. The results showed that the plant community density, cover, height and soil moisture content displayed a pattern of gradual increase, and the height, rootshoot ratio and root link length of R. soongorica displayed a pattern of gradual decrease, while the specific root length and root forks increased gradually with the slope aspect turned from south to west, east and north. The relationship between root forks and link length varied with the slope aspect: there was a highly significant negative correlation between the root forks and link length at north slope and south slope (P<0.01), whereas the correlation reached a significant level at the east slope and west slope (P<0.05). There was a tradeoff in resource allocation between the root forks and link length. The resource allocation mode in roots by reasonable tradeoff between root forks and link length with changes in slope aspect of habitat reflected the mechanism of biomass allocation and the adaptation strategy of R. soongorica populations under conditions of multiple competitions for resources in diverse habitats.

Key words: nitrogen fate, new shoot growing stage, apple tree, soil nitrogen budget, nitrogen level, germination stage