Shrub Afforestation Increases Microbial‐Derived Carbon in Arid Regions

Soil organic carbon (SOC) primarily originates from microbial and plant‐derived carbon (C). Afforestation activities significantly influence the retention of these C sources. However, in arid regions where SOC is particularly sensitive to external disturbance, the impact of afforestation on microbial‐ and plant‐derived C, and their relative contributions to SOC, remains poorly understood. To address this knowledge gap, we investigated the relative contributions of microbial‐ and plant‐derived C to SOC in three soil layers (0–20 cm, 20–60 cm, and 60–100 cm) by analyzing amino sugars and lignin phenol content. This analysis was conducted following the afforestation of Tamarix ramosissima at 3, 7, and 10 years in barren lands located within a desert–oasis ecotone on the southern edge of the Taklimakan Desert. Our results indicate that afforestation increased levels of SOC, nutrients (including ammonium nitrogen, nitrate nitrogen, and available phosphorus), and both microbial‐ and plant‐derived C across all soil layers. Specifically, microbial‐derived C content increased by 2.15–2.32 times, while plant‐derived C content increased by 41.06%–5.59 times. This resulted in a 28.26%–1.4 times increase in microbial‐derived C contribution to SOC. However, it reduced the relative contribution of plant‐derived C to SOC in the 0–60 cm soil layer by 7.6%–76.38%. Notably, the opposite pattern emerged in deeper soil layers (60–100 cm), where afforestation increased the plant‐derived C contribution to SOC by 2.23–4.31 times. Soil nutrients were identified as the primary factor influencing plant‐derived C accumulation. The alleviation of microbial nitrogen limitation (indicated by an increased vector angle) contributed to the accumulation of microbial‐derived C. These findings suggest that T. ramosissima afforestation enhances SOC sequestration, primarily through the accumulation of microbial‐derived C. This underscores the importance of microbial‐derived C to SOC dynamics in arid regions following afforestation.