Changes in soil organic carbon, nitrogen, phosphorus, and bulk density after afforestation of the “Beijing-Tianjin Sandstorm Source Control” program in China

·Cropland afforestation reduced soil carbon storage at the early stage.·Effect of afforestation on soil C varied with tree species and afforestation time.·Soil total N and P depletion were found in plantation sites after afforestation.·Populus tomentosa had a smaller depletion rate of soil C than Pinus tabulaeformis.·Soil C accumulation appears earlier than that of soil N and P after afforestation.

Under the “Beijing-Tianjin Sandstorm Source Control” (BTSSC) program in China, approximately 2.6 million ha of cropland have been converted into tree plantations during 2000-2010. Although a large amount of biomass carbon has been accumulated, less is known about the variations in soil organic carbon (SOC) and nutrients. This has hampered accurate prediction of SOC sequestration potential and sustainable soil development in the afforested region. This study used a space-for-time substitution method to evaluate four typical afforestation sites (Populus tomentosa, Armeniaca sibirica, 8a Pinus tabulaeformis, and 24a P. tabulaeformis sites) along with the corresponding control sites. The identified sites were used to assess the effects of plant species and afforestation time on soil carbon sequestration and physicochemical characteristics. While a significant SOC accumulation was noted in the 0-20 cm layer at the P. tomentosa and 24a P. tabulaeformis sites, SOC depletion occurred in the same soil layer at the A. sibirica and 8a P. tabulaeformis sites. Carbon sequestration at the 24a P. tabulaeformis site was 38.33 g C m− 2 yr− 1 in the 0-100 cm soil layer, but the other relatively younger tree sites showed carbon depletion in the range of 31.84-109.76 g C m− 2 yr− 1. The bulk density of the 0-20 cm layer significantly decreased at all the four sites. The largest decrease was at the P. tomentosa site, whereas no significant changes occurred in the 20-100 cm soil layers. Nitrogen and phosphorus depletion rate was higher in A. sibirica than in 8a P. tabulaeformis, which was in turn higher than that in P. tomentosa. The results suggested that afforestation hindered soil carbon storage and soil nutrient content but enhanced surface soil physical properties at the early stage of afforestation. The effects of afforestation varied with plant species and afforestation time. Soil carbon, nitrogen, and phosphorus depletion rates were higher in economic forests than in protective forests and were higher in evergreen coniferous forests than in broadleaved deciduous forests.