Effects of vegetation restoration on soil microbial necromass carbon and organic carbon in grazed and degraded sandy land

Vegetation restoration effectively enhances carbon (C) sequestration and supports the sustainable management of degraded ecosystems. However, its impact on the accumulation of microbial necromass C (NC) and soil organic C (SOC) in degraded and grazed sandy land remains unclear. This study evaluated six restoration types—grazing plot (control), grassland, scrubland, and forestland of Populus alba, Pinus tabuliformis, and Robinia pseudoacacia—to analyze microbial NC and SOC accumulation and identify the factors influencing these changes from the perspectives of soil nutrients, microbial structure, diversity, and activity. Compared with the grazing plot, SOC, bacterial NC, fungal NC, and microbial NC in restored sandy land increased by 64.2–140.9 %, 74.1–101.1 %, 135.7–221.4 %, and 41.5–63.8 %, respectively. The fungal NC:bacterial NC ratio was higher in restored land than in degraded land. Grassland exhibited a higher SOC content than Pinus tabuliformis and Robinia pseudoacacia, while Populus alba showed higher fungal and microbial NC contents than Robinia pseudoacacia. Soil total nitrogen (TN) and β-D-cellobiosidase were identified as key factors influencing SOC and microbial NC accumulation.This study highlights the critical role of vegetation restoration in enhancing soil C sequestration and promoting ecosystem sustainability. These findings provide a theoretical reference for ecological restoration and the sustainable development of degraded sandy land in regional desert steppe ecosystems.