Abstract: Fine root plays a key role in the water and nutrient uptake by plants. To accurately understand the fine root production, turnover, and decomposition is crucial for studying the carbon budget in terrestrial ecosystem. Taking the Alhagi sparsifolia community, a typical plant community in arid area of Xinjiang, as test object, and by using soil core sampling and fine root litterbags, this paper studied the fine root amount, its spatiotemporal variation, and decomposition and turnover patterns in the growth period (from May to October, 2010) of the A. sparsifolia. The monthly average fine root biomass of the community was 93.10 g·m^-2, of which, live and dead ones accounted for 72.72% and 27.28%, respectively. The fine root biomass showed an obvious seasonal variation trend, i.e., increased from May, peaked in late August, and declined gradually from September to October. 72.22% of live roots and 76.66% of dead ones were distributed in 0-30 cm soil layer, 13.82% of live roots and 13.39% of dead ones were distributed in 30-40 cm soil layer, and a little proportion of live roots were in the soil layers below 40 cm. The annual decomposition rate of fine roots was 64.52%, and it took 228 days and 916 days to decompose 50% and 95% of the total fine roots, respectively. The annual net production of fine roots was 118.81 g·m^-2·a^-1, and the annual turnover rate of fine roots was 1.75 cycles·a^-1. All the results showed that the fine root production of the A. sparsifolia community varied significantly with season and soil depth, and, due to the lower decomposition rate but higher turnover rate, the fine roots of A. sparsifolia community had great significance in the distribution pattern of underground carbon cycling in arid area ecosystem.

Key words: soil organic carbon (SOC), C3/C4 herbaceous plants, stable carbon isotope., riparian ecosystem