The study site was located in a degraded alpine grassland on the northern slope of Qilian Mountains, Gansu Province, China. Survey and sampling were carried out in 80 plots that were set up along four aspect transects of a hill with 20 m distance between adjacent plots. A handheld GPS was used to record latitude, longitude and altitude of each plot. ArcGIS was used to set up digital elevation model (DEM) to extract the information of elevation, aspect, and slope for each plot. The traits of plant communities were investigated and three individual samplings of M. przewalskyi were collected randomly in each plot. The samples were cleaned and divided into different organs. The roots were scanned with the Win-RHIZO for measurements of root forks and link length in laboratory, and biomass of different organs was measured after being dried at 80 °C in an oven. The 240 plots were categorized into groups of north, east, west and south aspects of slopes, and the linear regression analysis was then used to examine the trade-off relationship between root forks and link length in different groups.

With a change of the aspect from north to east, west and south, the density, aboveground biomass, height and soil moisture content of the plant community displayed a pattern of steadily declining, while the density, height, root link length of M. przewalskyi increased, and the root forks decreased. The number of root forks was negatively correlated with the link length in all aspects, but the relationship varied along the aspect gradient (p < 0.05). There was a highly significant negative correlation (p < 0.01) between the root forks and link length on north slope and south slope, whereas less significant (p < 0.05) on the east slope and west slope, all indicating a trade-off relationship between the root forks and link length. Consequently, the patterns of resource allocation between root forks and link length in different slope habitats reflected the response and adaption of plant root functional traits to their biotic and abiotic environments and the investment balance mechanism for root architecture construction.