Soil organic carbon plays a major role in the formation and stabilization of soil aggregates. However, our knowledge on the relationship between organic carbon and stable aggregate is not clear in the restoring process of degraded red soil. Red soil developed by granite has been eroded severely in southern China. Hetian town(25°33′-25°48°N, 116°18′-116°31′E) was one of the typical regions, located in Changting County, Fujian Province, China. The water stability of soil aggregates in five soils (include bare land; three ecosystems which were restored from severely eroded land to Pinus massoniana forest, Castanea mollissima plantation and Paspalum notatum Flugge grassland; protected second forest- next to the village) was measured with dry sieve and wet sieve, then different size aggregates (wet sieve) and whole soil were analyzed for organic carbon content. The influences of vegetation restoration on water stability of soil aggregates, organic carbon distribution in different size aggregates and relationship between organic carbon and stability of aggregate were discussed.
The stability of macroaggregate was lower in bare land than that in Pinus massoniana plantation forest, Castanea mollissima plantation and Paspalum notatum Flugge grassland, and the best one was in protective second forest. Organic carbon contents of different size aggregates were not changed in bare land. However, after vegetation restorated, organic carbon content and distribution proportion in different size aggregates were changed since organic material inputs increased. The macroaggregate had greater organic carbon content than the whole soil, microaggregate and silt and clay particles. The restoration speed of organic carbon in macroaggregate was faster than that in microaggregate and silt and clay particles. The proportion of organic carbon in macroaggregate comprised of about 15% of total organic carbon in 0-10cm soil layer of bare land, and the data were between 32% and 42% in other soils. After vegetation restored, the increase of carbon accumulated in soil macroaggregate, microaggregate and silt and clay particles accounted for 41%-51%, 24%-38% and 20%-31% of total increased carbon, respectively. The water stability of soil aggregates was related to soil organic carbon content. The higher concentrations of total organic carbon were recorded in the soils with higher aggregate stability.