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The root biomass distribution in alpine ecosystems (alpine meadow, alpine steppe, desert grassland and alpine desert) was investigated along a transect on the northern Tibetan Plateau in 2009. The results showed that roots were mainly concentrated in the 0-20 cm layer, and root biomass decreased exponentially with increasing soil depth. Root biomass was estimated to be 1,381.41 +/- A 245.29 g m(-2) in the top 20 cm soil, accounting for 85% of the total root biomass. The distribution pattern of the root biomass proportion along the soil profile was similar in different alpine ecosystems. The root biomass density varied with different alpine ecosystems and the total average root biomass was 1,626.08 +/- A 301.76 g m(-2). Root biomass was significantly correlated with average relative humidity, annual precipitation and soil organic matter. This indicates that precipitation and soil organic matter might be crucial for plant growth in the study area, while temperature is not an important factor controlling root growth.