Dynamics of glomalin-related soil protein and soil aggregates during secondary succession in the temperate forest

Despite the key role of glomalin-related soil protein (GRSP) in soil organic C (SOC) and soil aggregate stability, the influence of secondary successional processes on GRSP and the interrelationship of GRSP on SOC and its soil aggregate stability is unclear. Based on this, four stages of the secondary succession (including 20-, 32-, 47-, and 61-year-old stands) and the primary broad-leaved Korean pine (Pinus koraiensis) mixed forest were selected. The results showed that total GRSP (T-GRSP), easily extractable GRSP (EE-GRSP), SOC, mean weight diameter (MWD), and geometric mean diameter (GMD) all tended to increase with the secondary succession at 0-30 cm soil layer. The secondary succession contributed to the accumulation of GRSP content, so much so that after 61 years, both EE-GRSP and T-GRSP reached the level of the primary forest. EE-GRSP, T-GRSP, SOC, MWD, GMD, and GRSP/SOC significantly decreased with the deepening of soil depth in all successional stages. In addition, during the 20- and 32 year-old stands of secondary succession, the proportion of GRSP in the SOC was relatively high. With the progress of secondary succession, the content of macroaggregates (>0.25 mm) in the soil increased significantly and was not significantly different from the primary forest. The correlation analysis showed that T-GRSP was more correlated with SOC than EE-GRSP, while EE-GRSP was more correlated with MWD than T-GRSP. Additionally, there was also a significant positive correlation between MWD and SOC at 0-20 cm soil layer. Our results elucidate that GRSP may stabilize SOC pools by direct contribution to SOC in the early secondary succession, and the stabilizing effect on SOC is more pronounced in the later stages by forming macroaggregates. This enables us to understand the ecological functions played by GRSP in soil C sequestration and the enhancement of soil stability during the secondary succession.