Effects Of Different Vegetation Restoration Types On Herbaceous Communities And Soil Carbon And Nitrogen In The Loess Plateau

The Chinese Loess Plateau(CLP)is characterized by dense gullies and serious soil erosion,which is the main source of the Yellow River sediment and also an important ecological barrier in northern China.For a long time,the CLP has been a key area of national ecological protection and management.A series of restoration and management measures have been implemented,such as slope vegetation rehabilitation and soil erosion control,Both gully and slope erosion control and vegetation restoration,small watershed comprehensive management,returning farmland to forest and grassland,gully land consolidation,and gully consolidation and tableland protection.Small watershed is the most important geographical and geomorphic unit of the CLP.The comprehensive management of small watershed implemented in the 1980 s,which has played a crucial role in controlling soil erosion on the CLP.Natural vegetation restoration and artificial afforestation,as important methods of ecological management in small watershed of the CLP,have always been important research objects of ecological,hydrological and erosion research.Herbaceous community composition and soil carbon(C)and nitrogen(N)are the core contents of ecosystem research.However,at the small watershed scale,the differences and mechanisms of herbaceous community composition and soil C and N are not sufficiently studied.In the past,many studies were conducted at plot scale,but few studies was conducted at small watershed as a research unit.Therefore,this study takes the comparison of natural vegetation restoration(Dongzhuanggou)and artificial afforestation(Yangjiagou)catchments in the Nanxiaohegou watershed of Qingyang,Gansu province as the research object,and the methods of field investigation and laboratory physical and chemical analysis were used.The differences and influencing factors of herbaceous plant community composition,soil C and N in 0-20 cm surface layer and 0-100 cm soil profile in two comparative small cathments were studied.Explore the differences of ecological processes after natural vegetation restoration and artificial afforestation in small watershed of the Loess Plateau.To provide theoretical basis for scientific and rational formulation of vegetation restoration policy.The results are as follows:(1)The species diversity level of herbaceous plant community in the small watershed of natural restoration grassland is higher than that in the small watershed of artificial afforestation.Soil moisture and nutrients are the main factors for the differences of functional characteristics and diversity patterns of herbaceous communities in small watersheds of natural vegetation restoration and artificial afforestation.Topographic factors had no significant effect on functional traits and diversity patterns,while differences in soil moisture,nitrogen and phosphorus content led to differences in some traits between gully bottom and slope.(2)In the small watershed with natural vegetation restoration,slope gradient and aspect had no significant effect on the content of organic carbon and total nitrogen in the surface soil,and the content of organic carbon and total nitrogen in the surface soil of the middle slope was significantly higher than that of the upper slope and the lower slope;In the small watershed of artificial afforestation,slope has no significant effect on the content of organic carbon and total nitrogen in surface soil,and slope direction has no significant effect on the content of total nitrogen in surface soil.The content of organic carbon in surface soil of shady slope and semi shady slope is significantly higher than that of semi sunny slope and sunny slope,the content of organic carbon in surface soil of downhill and middle slope is significantly higher than that of upslope,and the content of total nitrogen in surface soil of middle slope is significantly higher than that of upslope;There was no significant difference in the contents of organic carbon and total nitrogen in the surface soil between natural grassland and artificial forest land at different slopes.The content of total nitrogen in the surface soil of semi sunny slope of artificial forest land was significantly higher than that of natural grassland,the content of organic carbon and total nitrogen in the surface soil of underground slope of artificial forest land was significantly higher than that of natural grassland,and the content of organic carbon in the surface soil of upper slope of artificial forest land was significantly higher than that of natural grassland.(3)The content and density of organic carbon and total nitrogen in the small watershed of natural vegetation restoration and artificial afforestation show a trend of gradually decreasing and gradually stabilizing with the increase of soil depth in the vertical direction.The content and density of organic carbon and total nitrogen in 0-20 cm soil layer are significantly higher than that in 20-100 cm soil layer.In the 0-100 cm soil layer,the content and density of soil organic carbon in the naturally restored grassland were significantly higher than those in the artificial forest,but there were differences between the two watersheds in different soil layers.The content of organic carbon in the 20-40 cm and 60-80 cm soil layers of the natural grassland was significantly higher than that in the artificial forest,while the density of organic carbon in the 0-20 cm,20-40 cm and 60-80 cm soil layers of the natural grassland was significantly higher than that in the artificial forest.There was no significant difference in soil total nitrogen content and density between natural restoration grassland and artificial restoration forest.