Abstract: By using LI-840 and LI-8100, this paper measured the carbon flux in herb layer as well as the soil respiration rate in different dune parts in southern Junggar Basin, Northwest China, and studied the seasonal and diurnal variation characteristics of the carbon flux in herb layer, the annual variation characteristics of soil respiration rate in different dune parts, and the effects of environmental factors on the carbon flux and the soil respiration rate. The carbon flux in the herb layer exhibited a unimodal pattern both in diurnal and seasonal scales. The diurnal carbon flux in herb layer had a large fluctuation during vigorous growth season. In the herb layer, the net carbon exchange (NEE) ranged from -2.5 to 0.02 μmol·m^-2·s^-1, the total productivity (GEP) ranged from -4.4 to -1.1 μmol·m^-2·s^-1, and the carbon flux after September was maintained at near 0. Through the analysis on the relationships between the carbon flux and environmental factors, it was observed that there was a positive correlation between the herb layer carbon flux and soil temperature and between the soil respiration and PAR, whereas a negative correlation between the GEP and PAR. The annual soil respiration rate in different sand dune parts (top, middle, and bottom) presented a bimodal dynamic pattern, and there existed significant differences in the soil respiration rate among different slope positions.

Key words: Beijing mountainous area, community, hydrogen and oxygen isotopes., water source