Abstract: Taking the 4 and 18-year-old artificial plantations and the natural stand of Caragana microphylla in Horqin Sandy Land as the objects, and through digging root system by layers, this paper investigated the features of C. microphylla root distribution in different vegetation zones, and studied the responses of C. microphylla in its biomass allocation, root/shoot ratio, and root distribution to dry environment. The C. microphylla tended to allocate more biomass to roots. Among the three vegetation zones, natural stand and 4 years old artificial plantation had the largest and the smallest proportion of belowground biomass, respectively. The root biomass decreased gradually with soil depth, and the roots were mainly distributed in the 0-100 cm soil layer. The biomass of the absorptive roots of 4 years old C. microphylla plantation was more distributed in surface soil layer, being significantly greater than that of 18 years old plantation and natural stand (P<0.05) in 0-50 cm soil layer. However, the 18 years old plantation and the natural stand had more absorptive root biomass in 50-100 cm soil layer. The conductive root biomass of natural stand in 50-100 cm soil layer was significantly greater than that of 4 and 18-year-old plantations. The relationships between the above and belowground biomass allocations of C. microphylla were characterized by allometry model.

Key words: acidic forest soil, ammonia-oxidizing bacteria (AOB), N cycling., ammonia-oxidizing archaea (AOA)