Effects of Natural Succession and Forest Landscape Restoration on Soil C and Aggregate-Associated C in the Central Loess Plateau, China

Abstract

Vegetation restoration is an effective measure for increasing the soil organic carbon (SOC) stock and mitigating the impacts of global warming. Grouping soil C according to aggregate particle size can help with more thoroughly understanding the dynamics of soil C during vegetation restoration. However, the dynamics of soil-aggregate-associated C after the restoration of different vegetation types remain unclear. As such, in this study, soil samples from the 0- to 10- and 10- to 20-cm soil layers in natural grasslands and plantations, which are the two most commonly used vegetation restoration types, were used to explore the dynamics of soil-aggregate-associated C for these different vegetation types. These grasslands and forestlands were converted from cropland since 1999. The results showed that soil and aggregate-associated C content were significantly affected by vegetation restoration types and soil depth. Vegetation restoration significantly increased the proportion of macroaggregates (> 0.25 mm) and soil C stocks; however, the improvements in soil aggregates and soil C stocks were similar for the two vegetation types. Vegetation restoration significantly increased the C content of aggregates of different particle sizes but only significantly increased the C stocks of soil macroaggregates, which had the highest C content among all the considered particle sizes. In addition, the contribution of macroaggregate C in the 0- to 10- and 10- to 20-cm soil layers to the soil C in the bulk soil also increased after vegetation restoration, reaching 57−64%. The results of random forest regression showed that the macroaggregate C content was the primary factor affecting the soil C stocks. This study demonstrated that natural succession and plantations have similar abilities to improve soil aggregates and soil C content in the central Loess Plateau and that the dynamics of macroaggregate C content dominate the dynamics of soil C stocks.