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Carbon accumulation is an important research topic for grassland restoration. It is requisite to determine the dynamics of the soil carbon pools [soil organic carbon (SOC) and soil inorganic carbon (SIC)] for understanding regional carbon budgets. In this study, we chose a grassland restoration chronosequence (cropland, 0 years; grasslands restored for 5, 15 and 30 years, i.e. RG5, RG15 and RG30, respectively) to compare the SOC and SIC pools in different soil profiles. Our results showed that SOC stock in the 0- to 100-cm soil layer showed an initial decrease in RG5 and then an increase to net C gains in RG15 and RG30. Because of a decrease in the SIC stock, the percentage of SOC stock in the total soil C pool increased across the chronosequence. The SIC stock decreased at a rate of 0·75 Mg hm−2 y−1. The change of SOC was higher in the surface (0-10 cm, 0·40 Mg hm−2 y−1) than in the deeper soil (10-100 cm, 0·33 Mg hm−2 y−1) in RG5. The accumulation of C commenced >5 years after cropland conversion. Although the SIC content decreased, the SIC stock still represented a larger percentage of the soil C pool. Moreover, the soil total carbon showed an increasing trend during grassland restoration. Our results indicated that the soil C sequestration featured an increase in SOC, offsetting the decrease in SIC at the depth of 0-100 cm in the restored grasslands. Therefore, we suggest that both SOC and SIC should be considered during grassland restoration in semi-arid regions. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Precipitation infiltration is the most important process for soil water supply of vegetation in the arid regions. Higher infiltration rate is advantageous for vegetation growth and maintenance in the arid areas. Four grassland types ( Medicago sativa, Agropyron cristatum, Caragana korshinskii and Stipa capillata) were selected in this study. Results showed that the infiltration capacity in the legume grasslands was about 30% higher than in the gramineous grasslands and the difference was significant ( p < 0·05). Furthermore, the infiltration rate in legume shrub-grassland was 16% less than the legume grasslands, but the difference was not significant ( p > 0·05). The below-ground biomass, total porosity, capillary porosity, soil organic matters and soil aggregate were the main factors to determine the soil infiltration rates. The capillary porosity and soil aggregate of the top soil presented significant negative effects on soil infiltration rate ( p < 0·05). The below-ground biomass in 10-30 cm soil layer was the most important factor, which significantly and positively correlates with the soil infiltration rate ( p < 0·01). It is possible to conclude that the legume grasslands presented the higher soil infiltration rate and promoted precipitation infiltration in the studied area. And the legume grasslands might be a more suitable option for vegetation restoration from the perspective of soil infiltration and water supply in the arid regions. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]