No abstract

In the semiarid Horqin sandy land of northern China, establishment of artificial sand-fixing shrubs on desertified sandy lands is an effective measure to control desertification and improve the regional environment. Caragana microphylla Lam. and Artemisia halodendron Turcz. ex Bess. are two of the dominant native shrub species, which are adapted well to windy and sandy environments, and thus, are widely used in revegetation programs to control desertification in Horqin region. To assess the effects of artificially planting these two shrub species on restoration of desertified sandy land, soil properties and plant colonization were measured 6 years after planting shrubs on shifting sand dunes. Soil samples were taken from two depths (0-5 cm and 5-20 cm) under the shrub canopy, in the mid-row location (alley) between shrub belts, and from nonvegetated shifting sand dune (as a control). Soil fine fractions, soil water holding capacity, soil organic C and total N have significantly increased, and pH and bulk density have declined at the 0-5-cm topsoil in both C. microphylla and A. halodendron. At the 5-20 cm subsurface soil, changes in soil properties are not significant, with exception of bulk density and organic C concentration under the canopy of A. halodendron and total N concentration under the canopy of C. microphylla. Soil amelioration processes are initiated under the shrub canopies, as higher C and N concentrations were found under the canopies compared with alleys. At the same time, the establishment of shrubs facilitates the colonization and development of herbaceous species. A. halodendron proved to have better effects in fixing the sand surface, improving soil properties, and restoring plant species in comparison to C. microphylla.

Livestock grazing is recognised as one of the main causes of vegetation and soil degradation/desertification in the semi-arid Horqin sandy steppe of northern China. In this paper, soilplant system carbon (C) in a representative degraded sandy grassland in the Horqin sandy steppe (42°58' N, 120°42'E altitude c. 360 m a.s.l.) was measured. Three situations: long-term continuous grazing (CG), exclosure for 5 years (5EX), and exclosure for 10 years (10EX), were compared to assess the effect of grazing management on C sequestration. Ground cover increased from the CG (35%) to the 5EX (63%) and to the 10EX (81%), and accordingly soil organic C at 0-15 cm depth and total plant components C increased from the CG (492 and 98 g m -2 ) to the 5EX (524and 134 g m -2) and to the 10EX (584 and 317 g m -2 ). The results suggested that continuous grazing in the erosion-prone sandy grassland is very detrimental to vegetation and soil. Under exclosure conditions, vegetation restoration and litter accumulation significantly increased plantsoil system C storage, and thus sequestration of atmospheric C. It was concluded that the degraded sandy grassland could contribute to significant C sequestration with the implementation of protective practices.

China's Horqin Sandy Land, a formerly lush grassland, has experienced extensive desertification that caused considerable carbon (C) losses from the plant-soil system. Natural restoration through grazing exclusion is a widely suggested option to sequester C and to restore degraded land. In a desertified grassland, we investigated the C accumulation in the total and light fractions of the soil organic matter from 2005 to 2013 during natural restoration. To a depth of 20 cm, the light fraction organic carbon (LFOC) storage increased by 221 g C/m 2 (84%) and the total soil organic carbon (SOC) storage increased by 435 g C/m 2 (55%). The light fraction dry matter content represented a small proportion of the total soil mass (ranging from 0.74% in 2005 to 1.39% in 2013), but the proportion of total SOC storage accounted for by LFOC was remarkable (ranging from 33% to 40%). The C sequestration averaged 28 g C/(m 2 •a) for LFOC and 54 g C/(m 2 •a) for total SOC. The total SOC was strongly and significantly positively linearly related to the light fraction dry matter content and the proportions of fine sand and silt+clay. The light fraction organic matter played a major role in total SOC sequestration. Our results suggest that grazing exclusion can restore desertified grassland and has a high potential for sequestering SOC in the semiarid Horqin Sandy Land.

Water is a limiting factor to plant growth in the Horqin Sand Land of China. Knowledge of soil saturated hydraulic conductivity (Kfs) is of importance because Kfs influences soil evaporation and water cycling under natural/artificial conditions at various scales. Kfs at fixed dunes and shifting dunes of the Horqin Sand Land were measured in situ by the Gueph permeameter. The results indicated that (1) Kfs ranged from 0.48 to 10.25 mm/min, and showed that Kfs of fixed dunes is bigger than it at shifting dunes; (2) Kfs at fixed dunes increased with increasing soil depths, but for shifting dunes, it diminished with increasing soil depths; (3) Kfs at fixed dunes is significant negative correlation with hardness, while it significant negative correlation with hardness and organic matter content at shifting dunes.