Influences of EICP treatment on the aggregate stability and soil organic carbon retention capacity of purple soil

Soil organic carbon (SOC) is one of the core components of carbon cycle in terrestrial ecosystem, its dynamic balance plays a vital significance for global climate change and agricultural sustainable development. The Three Gorges Reservoir area (TGRA) is a typical ecologically fragile region with characteristic of abundant rainfall concentrated in specific seasons, faces the challenge of severe loss in soil organic carbon. Enzyme-induced carbonate precipitation (EICP) is an emerging bio-mediated technology, has been applied in geotechnical stabilization and soil reinforcement, while its capacity to influence soil aggregate stability and organic carbon retention remains unclear. Therefore, taking purple soil in the TGRA as material, 4 EICP solution concentrations (0.5, 1.0, 1.5 and 2.0 mol/L) and control check (CK) were set, the variations in aggregate particle size distribution, aggregate stability and soil organic carbon retention capacity were evaluated under 7 maintenance durations (0, 1, 7, 15, 30, 60 and 120 d). Moreover, the influence factor influencing soil organic carbon retention capacity were determined. The results indicated that the microaggregate of purple soil rapidly transferred to macroaggregate (>0.25 mm) with the effect of EICP. Compared to that in the CK, the mean weight diameter (MWD), geometric mean diameter (GMD) and soil organic carbon retention capacity with EICP treated significantly increased by 101.43%-219.47%, 75.21%-271.56% and 20.87%-57.48% (P<0.05), respectively. Moreover, MWD, GMD and soil organic carbon retention capacity increased first and then decreased with increasing EICP solution concentration, and they increased rapidly and then tend to stable with increasing maintenance duration. Among them, MWD, GMD and soil organic carbon retention capacity of purple soil in the CK demonstrated negligible variation during the maintenance duration, while significant increases were observed under EICP treatments, with the 1 d increments of MWD, GMD and organic carbon retention capacity accounting for 53.32%-64.23%, 47.30%-52.92% and 63.61%-76.39% of the total increase, respectively. In addition, fractal dimension decreased initially followed by an increase as EICP solution concentration increases, while it decreased rapidly and then tend to stable with the increase of maintenance duration. Furthermore, correlation analysis indicated that the soil organic carbon retention capacity of purple soil under EICP treatments positively related to MWD and GMD, while negatively related to fractal dimension, with statistically significance (P<0.01). The fitting analysis showed that a highest determination coefficient was observed in the fitting function between MWD and soil organic carbon retention capacity, and can be employed as optimal indicator to evaluate the variation in soil organic carbon retention capacity of purple soil under EICP treatments. The results indicated that EICP can rapidly increase the aggregate stability and soil organic carbon retention capacity of purple soil, can provide a theoretical guidance for soil organic carbon retention in the TGRA.