Appropriate N addition improves soil aggregate stability through AMF and glomalin-related soil proteins in a semiarid agroecosystem

Soil aggregation and structural stability play a crucial role in soil organic carbon (SOC) sequestration. However, the underlying mechanisms of arbuscular mycorrhizal fungi (AMF) and glomalin-related soil protein (GRSP) responses to N addition and their impacts on soil aggregation and organic carbon stability remain unclear. Hence, a 16-year field N addition experiment on winter wheat (Triticum aestivum L.) was conducted to investigate the effects on the stability of soil structure and SOC fractions via AMF and GRSP. Overall, N addition increased the soil aggregate mean weight diameter (MWD), which exhibited an increase in the proportion of large macroaggregates and a decrease in the proportion of silt-clay fractions. Appropriate N (180 kg N ha(-1)) input increased SOC stability and total SOC stock, while excessive N (360 kg N ha(-1)) input increased labile organic carbon fractions, and active C index and decreased the C stock. The concentrations of SOC, total GRSP (T-GRSP), and easily extractable GRSP (EE-GRSP) showed the largest increases in small macroaggregates, and GRSP was significantly correlated with SOC, recalcitrant organic carbon, and MWD (p < 0.05). These results indicated that appropriate N addition promoted AMF to secrete GRSP, which in turn favoured large macroaggregation and enhanced the physical protection of SOC. Meanwhile, the increased GRSP stimulated the accumulation of recalcitrant C, thus improving soil organic carbon stability and carbon sequestration capacity. The study suggested that appropriate N addition (180 kg N ha(-1)) should be used to improve the carbon sequestration potential of farmland on the Loess Plateau.

Automated summary

Soil aggregation and structural stability are crucial for soil organic carbon sequestration. Appropriate nitrogen addition can promote arbuscular mycorrhizal fungi (AMF) to secrete glomalin-related soil protein (GRSP), enhancing the formation of soil aggregates and the physical protection of organic carbon, thereby improving soil organic carbon stability and carbon sequestration capacity.