关键词: 土壤有机碳, 植被类型, 黄土沟壑区, 坡地

Abstract: Vegetation recovery is an important measure to mitigate soil erosion and improve soil quality in the Loess Plateau.To understand the impact of vegetation recovery on soil quality,soil organic carbon (SOC) and total soil nitrogen(TSN)level and distribution characteristics along a slope under vegetation conditions were investigated on slope of Wangdonggou Watershed in Gully Region of Loess Plateau.Five experiment sites were set up along Fanjialiang.Site I to site Ⅳ along the eastern slope of Fanjialiang was Xingniugua,Dujiaping,Baiyanggua east and Bai-yanggua west,being adjacent to each other with similar slope and aspect.The vegetations were Prunus armeniaca L,orchard(Malus pumila),Robinia pseudoanacia and grass(Bothriochloaischaem- um(L.)Keng),respectively.Soil samples(0～20cm)at each site were taken from the upper slope,middle slope,lower slope and the foot slope,respectively.Site V at the western slope of Fanjialiang was Shaozhongwan with six vegetation types including Robinia pseudoanacia,arborvitae(Platycl- adus orientalis Endl.)、Chinese pine(P. tabulaeformis Carr),Hippophae rhamnoides L. subsp,Malus pumila and grass.Soil samples(0～60cm)were taken under vegetations.Types,population,and height of plants of each site were surveyed. The results demonstrated that compared with grassland,SOC content increased by 9.3%(P>0.05)for Chinese pine and decreased by 40.1%(P<0.05)for orchard.SOC content under Hippophae rhamnoides L.subsp.,arborvitae,and Robinia pseudoanacia was lower than that of grassland,but the difference was not significant(P>0.05).The level of SOC decreased with depth.For the site under grass,the content of SOC at lower slope and foot slope was respectively 47.6% and 62.9% higher than that at the upper slope with 7.8g·kg^-1.For the site of orchard,SOC content was 6.17g·kg^-1～6.69g·kg^-1 at the middle and foot slope,higher than that at the upper (5.54g·kg^-1).For the site of Robinia pseudoanacia,content of SOC varied from 8.55 to 10.50g·kg^-1,similar SOC along slope changes under orchard and Robinia pseudoanacia.For the site of Prunus armeniaca L.the content of SOC varied from 9.79g·kg^-1 to 14.41g·kg^-1,higher in the middle along the slope.In addition,there was a significant(R²=0.925)correlation between TSN and SOC. Intensive human disturbance resulted in lower SOC content in the region.Planting orchard on the slope significantly improved the productivity of soil,but it is not profitable to SOC accu-mulation.Some suggestions on vegetation construction in the region were put forward:1)vegetation types should be considered fully when vegetation regeneration and rehabilitation were carried out on the slopes in the region. 2)To adjust the growth conditions and increase input of SOC is essential to enhance SOC accumulation in the region.

Key words: gully region of Loess Plateau, slope, soil organic carbon, vegetation types