Glomalin-related soil protein affects soil aggregation and recovery of soil nutrient following natural revegetation on the Loess Plateau

The glomalin-related soil protein (GRSP) is an important fraction of soil organic carbon (SOC) and soil nitrogen (N), and is important for stabilization of SOC and soil aggregates. However, the effects of natural restoration on the concentration and allocation of GRSP differ for different soil aggregate sizes, and how size further affects SOC and soil N restoration, and stabilization of SOC and soil aggregates is not well understood. Here, we present the first characterization of the distribution of GRSP fractions and soil nutrients in soil aggregates following natural restoration by choosing fields of 0, 7, 12, 17, 22, 32 years after cropland abandonment, and a natural grassland as reference. GRSP concentration increased most in microaggregates after 32 years of natural restoration. The processes of rapid accumulation of GRSP (22 to 32 years) occurred simultaneously with the formation of macroaggregates, reduction of microaggregates, and rapid increase of mean weight diameter (22 to 32-years). The soil aggregate stability and contents of GRSP, SOC, labile carbon, total N and phosphorus in each soil aggregate fraction significantly increased in the late stage of natural restoration (22 to 32 years). The most recalcitrant carbon fraction in microaggregates significantly increased between 7 and 32 years (0.887 g kg(-1)). Our study suggests that abandoning farmland is effective for the restoration of GRSP, soil nutrients and structure and that microaggregates promote the accumulation of recalcitrant carbon and increase the stability of SOC largely through its ability to retain GRSP.