Abstract
The afforestation of abandoned farmland significantly influences soil organic carbon (OC). However, the dynamics between OC inputs after afforestation and the original OC are not well understood. To learn more about soil OC dynamics after afforestation of farmland, we measured the soil OC content in paired forest and farmland plots in Shaanxi Province, China. The forest plots had been established on farmland 18, 24, 48, 100, and 200 yr previously. The natural 13C abundance of soil organic matter was also analyzed to distinguish between crop- and forest-derived C in the afforested soils. We observed a nonlinear accumulation of total OC in the 0–80 cm depth of the mineral soil across time. Total soil OC accumulated more rapidly under forest stands aged 18 to 48 yr than under forest stands aged 100 or 200 yrs. The rate of OC accumulation was also greater in the 0–10 cm depth than in the 10–80 cm depth. Forest-derived OC in afforested soils also accumulated nonlinearly across time, with the greatest increase in the 0–20 cm depth. Forest-derived OC in afforest soils accounted for 52–86% of the total OC in the 0–10 cm depth, 36–61% of the total OC in the 10–20 cm depth, and 11–50% of the total OC in the 20–80 cm depth. Crop-derived OC concentrations in the 0–20 cm depth decreased slightly after afforestation, but there was no change in crop-derived OC concentrations in the 20–80 cm depth. The results of our study support the claim that afforestation of farmland can sequester atmospheric CO2 by increasing soil OC stocks. Changes in the OC stocks of mineral soils after afforestation appear to be influenced mainly by the input of forest-derived C rather than by the loss of original OC.
Highlights
Changes in land use have important effects on ecological processes and global climate change [1,2,3]
Where OCF and OCC are the concentrations of forest-derived C and crop-derived C, respectively; SOCF and SOCC are the stocks of forest-derived C and crop-derived C, respectively; and organic carbon (OC) and SOC are the total OC concentrations and OC stocks in afforested soil, respectively
Afforestation of cultivated soil increased total soil OC concentrations in the 0–40 cm depth by 88% and soil OC stocks by 81% when averaged across all stand ages
Summary
Changes in land use have important effects on ecological processes and global climate change [1,2,3]. During the past two decades, many studies have focused on the effects of land use change on the carbon content of ecosystems, in soils. These effects are not well understood due to large differences in climatic conditions, soil properties, and the type of land use change [2,4,5,6,7,8,9,10,11,12]. More than 20.7 million ha of abandoned farmland have been afforested in China through the ‘‘Grain-for-Green Project’’, which aims to reduce soil loss and land degradation in the western part of the country [17]
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