Abstract: To explore distribution characteristics of root area of the evergreen shrub,Sabina vulgaris growing in the contrasting habitats in semi-arid Mu Us sandland,the methods of root excavation and asymptotic equation y=1-β^d(β=depth coefficient, d=soil depth(cm), y=fraction of root area from soil surface to depth d)were used in this paper.The results showed as follows:(1)Root area index(RAI=root area/soil surface area,m²/m2)decreased with decreased soil water availability,which benefits to alleviate below-ground competition of the plants for water and to make better economical use of the limited water resource in the long run.(2)The values of β (depth coefficient)、R_max(maximum depth of root system)、R₅₀(depth of root system including 50% total root area)、R₉₀(depth of root system including 90% total root area)increased with decreasing soil water availability,which means that depth of root system of S.vulgaris has compensation effect for decreasing water content of soil through deepening its depth.(3)Distribution characteristics of root area might record the change of water regime in the habitats,could provide some evidence on community succession to some extent as well.

Key words: S.vulgaris, Root area index(RAI), Cumulative root area(CRA), Cumulative root fraction(CRF), Depth of root system, Soil water availability