Forestation delivers significantly more effective results in soil C and N sequestrations than natural succession on badly degraded areas: Evidence from the Central Loess Plateau case

Abstract

Vegetation restoration is an important factor affecting soil carbon (C) and nitrogen (N) sequestration. However, the effects of the type of vegetation restoration on soil C and N sequestration varies owing to different environmental conditions. Therefore, additional studies should explore the effects of vegetation restoration type on soil C and N sequestration, especially between natural restoration and artificial afforestation. This study explored the differences in improving soil C and N sequestration between artificial forests (AF) and natural grasslands (NG) that had been converted from sloping cropland over 20 years since the implementation of GGP (Grain for Green Program) on the Central Loess Plateau, China. The results showed that NG and AF significantly increased the 0–20 cm soil organic carbon (SOC) content but had a minimal impact on the 20–100 cm SOC content after 20 years of vegetation restoration. In addition, the two vegetation restoration types significantly increased the 0–60 cm soil total nitrogen (STN) content, but they both had no significant effects on the 60–100 cm soil layer. Moreover, the C and N sequestration capacities of AF were higher than those of NG due to the AF had higher plant biomass and lower plant biomass C:N ratios compared to NG. The AF and NG both significantly increased the soil aggregate structure and stability following cropland conversions. Apart from soil aggregates playing a crucial role in affecting soil C and N sequestration, plant biomass and its C:N ratios also had the most substantial effects. The results suggested that soil aggregate stability and the quantity and quality of input organic matter have strongly influenced soil C and N sequestration post-restoration; moreover, N fixing species is more conducive to soil C and N sequestration and the artificial forests had higher C and N sequestration capacities than natural grasslands in the Loess Plateau, with a mean annual precipitation of 505 mm.