Dynamics and stabilization of soil organic carbon after nineteen years of afforestation in valley‐type savannah in southwest China

Abstract

AbstractSerious concerns about carbon (C) sequestration capacity and the stabilization of sequestered C in forested soils have emerged in the context of global climate change. The organic C in soil and in soil fractions at four sampling times in Acacia auriculiformis plantations afforested in 1991 were investigated with a combination of density fractionation and acid hydrolysis techniques. The results showed that the accumulation of C in the forested soils had accelerated because the afforestation of wasteland with A. auriculiformis. The C accumulation rates of the surface and subsurface soils averaged 0.38 and 0.17 t C/ha/yr, respectively, during the 19 yr following the afforestation. The percentage of organic C in heavy fraction relative to total soil organic C at the surface soil was 71% in 2003. This value was significantly (P < 0.05) higher than that in 2010 (68%). The chemical recalcitrant C index of light fraction was significantly (P < 0.05) higher than that of heavy fraction in 2003 regardless of soil depth, but both decreased with time. ca. 58–68% of the newly sequestered C was protected by physical mechanism, and 41–50% was transferred into the acid nonhydrolysable fraction during the 12–19 yr after the trees were planted. The chemical stability of the physically protected C remained lower than that of the unprotected C following the afforestation in the valley‐type savannah. However, both the stability values showed a decline with time.