Soil organic carbon and nitrogen pools in reclaimed mine soils under forest and cropland ecosystems in the Loess Plateau, China

•SOC and N pools in reclaimed mine soils were explored.•SOC and N pools varied among forest and cropland plots.•R. pseudoacacia-P. tabulaeformis forest facilitated SOC and N accumulation.•Sequestration rates of SOC and N in cropland followed a polynomial function.•SOC and N negatively correlated with soil pH.

Reclamation of opencast coal mine significantly ameliorates the degraded edaphic characteristics. The long-term changes of carbon (C) and nitrogen (N) pools in reclaimed mine soils (RMSs) in the Loess Plateau, China, have not been sufficiently elucidated. In this study, six types of reclaimed forest stands (with similar reclamation age between 22 and 25-year) and three age chronosequence reclaimed croplands (2-, 7-, 18-year of reclamation) were identified in Pingshuo opencast coal mine, Shanxi Province, to determine SOC and N pools in RMSs. Adjacent, undisturbed sites of forest and cropland and unreclaimed plots were selected as references as well. The results showed that 22-25 years after reclamation, SOC and N pools differed significantly among forest RMSs, ranging from 11.66 to 69.10 Mg ha−1 and 945.14 to 3145.83 kg ha−1, respectively, among which R. pseudoacacia-P. tabulaeformis forest had the greatest SOC and N pools and sequestration rates. Moreover, SOC and N pools in cropland RMSs increased across reclamation age chronosequence, ranging from 6.44 to 19.49 Mg ha−1 and 666.55 to 1554.73 kg ha−1, respectively. The sequestration rates of SOC and N in cropland RMSs followed polynomial function across age chronosequence. C:N ratio varied among plots and tended to be higher in RMSs under the mixed forest of trees. SOC and N pools were negatively correlated with soil pH. Our study indicated that SOC and N pools could be improved across age chronosequence through well managed vegetation restoration. R. pseudoacacia-P. tabulaeformis mixed forest and H. rhamnoides monoculture forest could be effective reclamation patterns to restore SOC and N pools in Pingshuo opencast coal mine.