Profile Distributions and Controls of Soil Inorganic Carbon along a 150-Year Natural Vegetation Restoration Chronosequence

Soil inorganic C (SIC) comprises approximately a third of the global soil C pool, which plays an important role in global C cycling. However, there is still considerable disagreement on the direction and magnitude of changes in SIC stocks following vegetation restoration. We conducted a study comparing SIC at different succession stages along a 150-yr natural vegetation restoration chronosequence to examine the effect of long-term natural vegetation restoration on the distribution of SIC and to identify the factors that control changes in SIC. The results showed that SIC storage in the top 10 cm gradually decreased (0.092 Mg ha(-1) yr(-1)) along the vegetation restoration chronosequence but was basically unchanged in the subsoil (10-100 cm). The soil total C storages remained stable across the restoration sequence, with the redistribution of the total soil C pool from SIC to soil organic C (SOC) the dominant forms. The controlling factors of SIC were different in the top- and subsoils along the chronosequence. In the top 30-cm soil layers, SOC was a good predictor of SIC; however, for soils below 30 cm, soil sand and silt contents and pH were better predictors of SIC. Therefore, we can conclude that the variations in SOC induced by vegetation restoration were the main driving force for SIC changes in the topsoil, while the genetic soil features (i.e., sand and silt contents) were the controlling factors that determined the amount of SIC in the subsoil.