Abstract
A multitude of studies analyzed the dynamics of soil organic carbon (SOC), but their methodology does not provide sufficient understanding of the differential impact of artificial and natural afforestation on SOC dynamic. We investigated the SOC dynamics following artificial (AR) and natural (NQ) afforestation on abandoned farmland (AF) in China’s Loess Plateau in an attempt to evaluate the effects of these afforestation methods. We characterized soil structure and stoichiometry using stable isotope carbon and radiocarbon models. We aim to compare SOC dynamics, clarify SOC sources under different afforestation, examine comparability of the study areas and ascertain how soil aggregate size classes control SOC dynamics. The 0-10 cm and 10-20 cm SOC stocks were significant higher in NQ than AR and AF. At other depths, there is no significant difference among the three land-use systems. Total topsoil SOC stocks, C:N and C:P of differently sized soil aggregates significantly increased following afforestation. Carbon isotope analysis results indicated that the SOC decomposition rate and the new SOC input rate were lower under NQ than AR. Afforestation can lead to SOC accumulation in soil depths up to 1m mainly because the topsoil (0-20 cm) changes significantly. SOC resources are mainly from macroaggregate formation provided by fresh plant residues. The comparability of study sites is validated, so the“space-for-time substitution” method is applicable in this study.
Highlights
Soil contains vast and dynamic pools of organic carbon that are fundamental for maintaining the balance of atmospheric CO2 concentrations (Lal 2004; Post et al.1982).The soil organic carbon (SOC) pool and its dynamics are important properties of ecosystems (Schmidt et al 2011)
SOC loss from soil respiration was derived from microaggregates during afforestation
The SOC stock and content in 0-10 cm soil significantly increased with both artificial afforestation dominated by plantation of Robinia pseudoacacia L (AR) and natural afforestation dominated by natural forest Quercus liaotungensis Koidz (NQ)
Summary
Soil contains vast and dynamic pools of organic carbon that are fundamental for maintaining the balance of atmospheric CO2 concentrations (Lal 2004; Post et al.1982).The soil organic carbon (SOC) pool and its dynamics are important properties of ecosystems (Schmidt et al 2011). Rapid population growth combining with climate and environmental conditions in the area have resulted in severe soil erosion in the Loess Plateau (Shi et al 2017). From 1950s to mid-1960s, the principle soil conservation strategies were terracing on cultivated slopes and planting trees on uncultivated slopes. From late 1970s to late 1990s, terracing became the first principle soil conservation strategy and natural rehabilitation appeared in some places (Zhou et al 2013). The Grain for Green project was implemented in 1999 to halt soil erosion and promote ecological restoration in the region. As part of this project, both natural and artificial afforestation have been promoted as methods of ecological restoration (Shi et al 2011)
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