Content and factors influencing glomalin-related soil protein of alfalfa fields at different growing ages

Glomalin-related soil protein (GRSP) originates from residual arbuscular mycorrhizal fungi (AMF), which could promote the formation of soil aggregates. This study used Zea mays farmland as the control and Medicago sativa grassland with different planting years (L₂₀₁₉, L₂₀₁₂, L₂₀₀₃) as the research object to analyze the main factors affecting GRSP content and the relationship between GRSP content and soil organic carbon (SOC) and aggregate characteristics through a long-term positioning experiment in the semi-arid area of the Loess Plateau. The results showed that AMF abundance (Colonization rate and Hypha density) and GRSP content significantly increased with increasing alfalfa planting years (P < 0.05). Linear regression analysis showed that Total Glomalin Related Soil Protein (T-GRSP) content positively correlated with SOC and microbial biomass carbon (P < 0.05), and that Easily Extractable Glomalin Soil Protein (EE-GRSP) content and Total Glomalin Related Soil Protein (T-GRSP) content correlated positively with mean weight diameter (MWD) and aggregate content greater than 0.25 mm (R_0.25) (P < 0.05) of aggregate characteristics. Compared with Z. mays farmland, the main environmental factors affecting soil AMF abundance and GRSP content were soil-available phosphorus (P = 0.002) and microbial biomass carbon (P = 0.002). The proportion of T-GRSP in SOC was increased with an increase in M. sativa grassland planting years, indicating that continuous cultivation of M. sativa caused the increased GRSP content, promoted the accumulation of GRSP content in SOC, and improved the contribution of GRSP content to the stability of soil aggregates and organic carbon. The results can provide a reference for the study of GRSP in yellow soil and sustainable utilization of M. sativa cultivation grassland.