Accumulation of carbon and nitrogen in the plant–soil system after afforestation of active sand dunes in China's Horqin Sandy Land

•China's Horqin Sandy Land is a seriously desertified region of northern China.•Afforestation with Mongolian pine sequestered 678 kg C ha−1 y−1 over 38 years.•It also sequestered 23 kg N ha−1 y−1 during the same period.•The strongest effects on soil C and N appeared in the upper 20 cm of the soil.•The C:N ratio may change due to the differences in C and N partitioning.

Afforestation of drylands is a potentially effective option to sequester carbon and to restore degraded soils and ecosystems. In China's Horqin Sandy Land, we investigated the effects of afforestation using Mongolian pine (Pinus sylvestris var. mongolica Litv.) in areas with active sand dunes on carbon (C) and nitrogen (N) storage in the plant–soil system. The 28- and 38-year-old plantations had 72 and 160 times the ecosystem biomass C storage, respectively, of areas with active sand dunes; the corresponding ecosystem biomass N storage was 48 and 105 times the value for areas with active dunes, versus 1.8 and 2.3 times for soil total C (organic plus inorganic) storage and 1.4 and 1.5 times for soil total N storage. The C and N accumulation rates in the plant–soil system were 678 kg C ha−1 y−1 and 23 kg N ha−1 y−1, respectively, over 38 years. The remarkable effects of afforestation on soil C and N primarily appeared in the upper 20 cm of the soil. Our results indicated that afforestation of active sand dunes with Mongolian pine has high potential to sequester C and N in the plants and the soil. The biomass played a more important role than the soil for C sequestration, but the soil played a more important role than the biomass for N sequestration.