Soil aggregation and intra-aggregate carbon fractions in relation to vegetation succession on the Loess Plateau, China

• Vegetation succession caused an increase in small macroaggregates.
• Bulk soil carbon and aggregate carbon increased with recovery time.
• iPOM-C may be used for early detection of carbon changes after vegetation restoration.

Revegetation has been reported to be one of the most effective measures for reducing soil erosion on the Loess Plateau in China. The Yunwu observatory, located in the northwestern Loess Plateau of China, was selected to study the effect of vegetation succession on total carbon (C), aggregate C, and intra-aggregate particulate organic matter-carbon (iPOM-C) concentrations. The vegetation types studied, listed from the shortest to the longest enclosure duration order, were abandoned grazed grassland (Ab.G3), Hierochloe odorata Beauv. (Hi.O7), Thymus mongolicus Ronnm (Th.M15), Artemisia sacrorum Ledeb (At.S25), Stipa bungeana Trin Ledeb (St.B36), and Stipa grandis P. Smirn (St.G56) communities. Five sizes of aggregates were separated using the modified Yoder method (< 0.25 mm, 0.25–1 mm, 1–2 mm, 2–5 mm and 5–8 mm). Fine and coarse iPOM-C concentrations were isolated from the soil aggregates. The results showed that revegetation led to an increase in the percentage of aggregates in small macroaggregates (0.25–2 mm) and thereby improved the uniformity of the soil aggregate size distribution. The concentration of bulk soil carbon ranged from 10.1 g kg− 1 to 29.7 g kg− 1 during vegetation succession. During the vegetation succession, with the exception of At.S25, the bulk soil carbon and aggregate carbon concentrations increased with recovery time. The fine iPOM-C concentrations were between 0.7 and 14.0 g kg− 1, which was significantly greater than the coarse iPOM-C concentrations. The coarse and fine iPOM-C concentrations exhibited different trends with vegetation restoration. In conclusion, vegetation restoration caused an increase in small macroaggregates, enhancing the uniformity of the soil aggregate size distribution and inducing greater soil organic carbon sequestration.