Allocation of soil organic carbon in physical fractions was measured in mobile sand dune

and stabilized sand dune usingPinus sylvestris var.Mongolica(22year forest land)andCaragana microphylla(24year shrub land)in Horqin sandy land.Results show that(1)the contents of coarse sand

very fine sand andclay+silt

and electric conductivity increased while fine sand content and soil bulk density decre-ased in woodland

compared with mobile sand dune

(2)the whole SOC storage increased by 729% with an increment of 357g/m2 in forest land

and by 1050% with an increment 514g/m2 in shrub land

(3)dry organic mattersin light fractions account for 0.08%

1.24% and 1.14% of the total soil weights

while carbon storages inlight fractions are 9.7

182.5 and 185.9g/m2

accounting for 20%

45%and 33% of whole SOCs in themobile sand dune

forest land

and shrub land

respectively

(4)the allocations of SOC in particle-size fractions were in orders as fine sand>coarse sand>very fine sand>clay+ silt for the mobile sand dune

coarsesand>fine sand>very fine sand>clay+silt for the forest land

and coarse sand>very fine sand>fine sand> clay+silt for the shrub land

and(5)the variations of light fraction carbon were more sensitive than thewhole SOC after sand dune stabilization.Also

the increase of unprotected organic matter within coarse sandfraction played an important role in the change of whole SOC.