In order to understand the effects of different plantation types on soil organic carbon accumulation

we conducted a comparative analysis on the variations in the total amount and distribution characteristics ofsoil organic content in the 0-60cm soil layers of typical plantations of Robinia pseudoacacia

Hippophaerhamnoides

Caragana intermediain the loess hilly region.The results showed that the plantations playedpositive roles in soil organic carbon accumulation.After reaching their stable growth stages

the plantationsshowed replenishment effects on the soil organic carbon pool.The replenishment ability of the plantationscould be ranked in a decending order as Hippophae rhamnoides>Robinia pseudoacada>Caragana intermedia

with average annual replenishment rates of 0.854

0.004and 0.003g

respectively.Owing to thedifferences in root growth distribution

the replenishment rates varied vertically for different plantations.Under the plantation of Hippophae rhamnoides

the increase of soil carbon mainly occurred at the 20-40cmlayer with an annual replenishment rate of 0.357g

while for Robinia pseudoacada and Caragana intermedia

the increases were found at the layers of 40-60cm with rates of 0.010and 0.005g/kg

respectively.Moreover

the results also indicated significant correlation between soil physical properties and soil organiccontent(p<0.01);the soil organic content decreased with increasing soil bulk density and increased with aggregate stability.This suggested that the soil organic carbon storage capacity was affected by the soil physical properties

which in turn could be changed by vegetation root activities.