A typical artificial Robinia pseudoacacia plantation was used to study the characteristics of daily and seasonal soil carbon flux variation

and the changes of soil carbon flux components in different stand ages (12

14

15

18 a) at Tianjiagou soil and water conservation technology garden of the Longdong Loess Plateau. Soil carbon flux was monitored using the infrared gas analysis technology and the grassland was used as control. The results indicated that the daily soil carbon flux of different ages showed significant difference (P<0.01). The diurnal soil carbon flux trend presented a single peak curve

the highest value occurred in the daytime (13:00—15:00) while the lowest was detected at night (2:00—5:00). In addition

seasonal soil carbon flux exhibited significant difference of different ages (P<0.01)

The seasonal trends were in the order of summer > spring > autumn > winter. Soil carbon flux in summer was 8.78 to 20.32 times larger than that in winter. Soil carbon flux in spring was mainly with autotrophic respiration

while in summer and autumn with heterotrophic respiration

the contribution rate of autotrophic and heterotrophic respiration was basically the same in winter. For the grassland

soil carbon flux was mainly based on heterotrophic respiration in spring

summer and autumn

which was similar to R. pseudoacacia plantation in winter. The soil carbon flux of R. pseudoacacia plantation increased with the stand age with the annual soil carbon flux of 2 069.63 to 4 590.35 g/m2. The annual soil carbon flux of grassland was 2 806.27 g/m2

which was lower than that of the 18 a R. pseudoacacia plantation but higher than that of the other stand ages. Our study could provide a scientific basis for soil carbon sequestration and management measures of artificial R. pseudoacacia plantation in Longdong Loess Plateau.