Abstract: Exploring the relationship between soil organic carbon (SOC) and root distribution is essential for evaluating carbon stock and sequestration potential in terrestrial ecosystems. However, the relationship between SOC and root in shrub communities in desert grassland of China is not clear yet. In this study, we selected five shrub communities Haloxylon ammodendro and Caragana intermedia with deep root but root biomass concentrated in the shallow soil layer, Nitratia tangutorum with deep root and root biomass not concentrated in the shallow soil layer, Reaumuria songarica with shallow root and root bimass concentrated in the shallow soil layer, Sarcozygium xanthoxylon with shallow root but root bimass not concentrated in the shallow soil layer, to explore the relationship between SOC and root biomass in shrub communities. Root biomass density (RBD) and soil organic carbon density (SOCD) in different soil layers of a 0-100 cm soil profile were investigated. Our results showed that (1) the SOCD in the 0-100 cm soil profile was positively correlated with the RBD in 0-20 cm layer, while it had no significant correlationship with RBD in other layers; (2) the SOCD in 100 cm soil profile of H. ammodendron community was significantly lower than those of the other communities (P<0.01), however, there were no significant differences among the other four communities (P>0.05); (3) the vertical distributon of SOCD in H. ammodendro, C. intermedia and R. songarica communities were similar with the root distribution of communities and their dominant species, but in N. tangutorum community, it was similar with the root distribution of dominant species. In S. xanthoxylon community, it was only similar with the root distribution of community in 0-40 cm soil. This study indicated that the SOC in 0-100 cm soil profile of shrub communities was significantly associated with root biomass in 0-20 cm soil, and the vertical distributions of dominant shrub root system was a key factor affecting the vertical distribution of SOC.

Key words: aggregation intensity, distribution pattern, sampling scale, pattern size, Juglans cathayensis