Variation in glomalin in soil profiles and its association with climatic conditions, shelterbelt characteristics, and soil properties in poplar shelterbelts of Northeast China

Glomalin-related soil protein (GRSP) sequesters large amounts of carbon and plays important roles in maintaining terrestrial soil ecosystem functions and ecological restoration; however, little is known about GRSP variation in 1-m soil profiles and its association with stand characteristics, soil properties, and climatic conditions, hindering GRSP-related degraded soil improvement and GRSP evaluation. In this study, we sampled soils from 1-m profiles from poplar (Populus spp.) shelterbelts in Northeast China. GRSP contents were 1.8-2.0 times higher in the upper 40 cm soil layers than at 40-100 cm. GRSP-related soil organic carbon (SOC) sequestration in deeper soil layers was 1.2 times higher than in surface layers. The amounts of GRSP-related nutrients were similar throughout the soil profile. A redundancy analysis showed that in both surface and deeper layers, soil properties (pH, electrical conductivity, water, SOC, and soil nutrients) explained the majority of the GRSP variation (59.5-84.2%); the second-most-important factor in GRSP regulation was climatic conditions (temperature, precipitation, and altitude), while specific shelterbelt characteristics had negligible effects (< 5%). Soil depth and climate indirectly affected GRSP features via soil properties, as manifested by structural equation model analysis. Our findings demonstrate that GRSP is important for carbon storage in deep soils, regardless of shelterbelt characteristics. Future glomalin assessments should consider these vertical patterns and possible regulating mechanisms that are related to soil properties and climatic changes.