Shrub Encroachment: A Catalyst for Enhanced Soil Nutrients Storage in the Altai Mountains

Shrub encroachment in grasslands has a major impact on soil carbon storage (SOC_S) and soil total nitrogen (STN_S), which affects nutrient cycling and ecosystem processes. We explored the effects of shrub encroachment on SOC_S and STN_S in five grassland types in the Altai Mountains: mountain meadows, temperate meadow steppe, temperate steppe, temperate steppe desert, and temperate desert steppe. Shrub encroachment considerably improved SOC_S and STN_S, with the greatest increases occurring in locations with high encroachment. The interaction between grassland type and encroachment extent also significantly influenced soil properties, including bulk density, soil water content, and microbial carbon and nitrogen. Specifically, SOC_S increased by 16%, 77%, and 129%, and STN_S increased by 43%, 94%, and 127% under low, medium, and high shrub encroachment, respectively. The soil stoichiometry shifted, with C/N ratios decreasing and C/P and N/P ratios increasing with shrub encroachment. Structural equation modeling (SEM) revealed that shrub encroachment indirectly affected SOC_S and STN_S through changes in soil nutrients and climate. Our findings suggest that shrub encroachment promotes soil C sequestration and alters soil nutrient cycling, with implications for grassland management and ecological restoration in the face of global climate change.