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Abstract: In the semi-arid Kerqin Sandy Land of north China, land desertification and frequent sand storms in the spring strongly affect the growth of grassland vegetation and crops, and give rise to large reductions in yield as a result of wind erosion and sand dune movement. To bring desertification under control and reduce its influence on grassland and farmlands, many measures have been developed and implemented for stabilizing mobile sand dunes and restoring desertified grasslands. This study was conducted from 1996 to 2003 to evaluate the effectiveness of desert land restoration after implementation of sand-fixing measures. The results showed that construction of straw checkerboards and planting of shrub seedlings significantly enhances topsoil development on the dune surface, increasing silt and clay content and facilitating accumulation of soil carbon and total N, as well as accelerating an increase in plant diversity, vegetation cover and plant density. These findings suggest that using straw checkerboards and planting shrubs are successful methods for mobile sand dune stabilization and desertified grassland restoration in semiarid regions. The mechanism creating these changes is a reduction in wind erosion and improvement of the soil environment for plants. In addition, our results showed that construction of straw checkerboards was slightly more effective in vegetation and soil restoration in comparison with planting shrub seedlings, especially at the primary stage. [Copyright &y& Elsevier]

Abstract: Resorption of nutrients before leaf death and abscission is an important energy conservation mechanism employed by plants to endure nutrient limitation. However, leguminous N-fixing plants are able to acquire N through biochemical fixation, so are less dependent of soil N availability, and thus probably resorb less N. In the semi-arid Horqin Sandy Land of North China, Caragana microphylla, a leguminous N-fixing shrub, is the dominant plant species and is widely used in vegetation re-establishment programs to stabilize shifting sand. In this study, green- and senesced-leaf nutrient concentrations of C. microphylla were examined to compare nutrient resorption patterns along an age sequence of plantations (11, 19, 27 and 36 years, respectively) and to detect if nutrient resorption was affected by soil nutrient availability. The results showed that there were significant effects (p <0.01) of C. microphylla plantation age on nutrient resorption. N and P resorption efficiency decreased from 40% and 68%, respectively in the 11-yr old plantation to 32.0% and 55% in the 36-yr old plantation, while N and P concentrations of senesced leaves (indicators of resorption proficiency) increased from 17.5 and 0.56mgg−1, respectively in the 11-yr old plantation to 24.8 and 0.91mgg−1 in the 36-yr old plantation. Furthermore, N and P resorption proficiency of individual shrubs were negatively related to available N and P in the soil under the shrub canopy within and among plantations. This indicates that more foliar N and P was resorbed in lower nutrient sites and implies that C. microphylla in nutrient-poor environments is less dependent on day-to-day nutrient uptake and thereby adapted to severely desertified regions. Additionally, C. microphylla in the present study showed incomplete resorption of nitrogen, which suggests senesced-leaf fall returns highly decomposable litter to the soil, and thereby indirectly improves soil nutrient availability. The restoration of desertified land, therefore, may be accelerated with plantations of the N-fixing leguminous shrub C. microphylla. [Copyright &y& Elsevier]

Abstract: Overgrazing is a primary agent to cause and aggravate desertification in the Horqin Sandy Grassland of northern China that has reduced the capacity of carbon (C) and nitrogen (N) storage in the region. Grazing exclosure practice is recommended to control the desertification by vegetation restoration. How the restoration improves the C and N storage needs to be answered to the policy makers for their future land use planning and decisions. This storage in a plant–soil system down to 100cm inside grazing exclosure after practice terms of 7, 12, and 25 years was measured as compared to active sand dunes referred as exclosure practice term of 0. Organic C storage in the system increased by 341, 822, and 1786gm−2, respectively, after 7, 12, and 25 years of grazing exclosure, whereas the corresponding N storage increased by 30, 65, and 139gm−2. Soil is the major reservoir in the system to store C and N. Temporally along the exclosure terms of 0, 7, 12, and 25 years, the soil C storage comprised 97, 88, 77, and 84% of total plant–soil system C storage, respectively, whereas the corresponding soil total N storage comprised 99, 97, 94, and 94% of total plant–soil system N storage. Our results provide land use policy makers with rationale how to manage the grazing practice to restore the vegetation for C and N sequestration. [Copyright &y& Elsevier]