Abstract: Fine root plays a significant role in plant community performance of functions, soil carbon pool and global carbon recycling. Observation was done of biomass, decomposition and turnover of the fine roots of Haloxylon ammodendron communities in the Sanjiang River Valley throughout the whole growing season from May to October in 2010, using the soil columen method and the litter bag method. Results show that fine root biomass of the H. ammodendron communities varied significantly with the seasons. It increased gradually in the period from May to August, peaked in August, and then declined gradually in September and  October, and its monthly average reached 183.76 g•m^–2, of which live fine root accounted for 72.59% and dead one for 27.41%. And its distribution varied with soil depth, showing a trend of increasing first and then declining, with a major portion distributed in the >10-30 cm soil layer, accounting for 51.36% of the live fine root and 51.81% of the dead one. The annual decomposition rate of the fine root was 58.76%. It took 279 days and 1302 days for the decomposition rate to reach 50% and 95%,respectively. The net productivity of the fine root was 110.73 g•m^–2•a^-1, and its annual turnover rate wereas 1.25 times•a^-1. In conclusion, the fine root production of H. ammodendron communities varied significantly with season and soil depth. These findings suggest that the fine roots of H. ammodendron communities are of great significance for underground carbon recycling in the arid area.

Key words: Haloxylon ammodendron, fine root turnover, biomass, soil organic carbon