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Plant restoration leads to divergent sequestration of soil carbon and nitrogen in different fractions in an arid desert region

Soil organic carbon (OC) and nitrogen (N) associated with particle size fractions can be used as sensitive indicators to evaluate impacts of land use change on soil total OC (TOC) and total N (TN) pools. Aeolian sandy‐soils were collected from seven sites in the Tengger Desert, representing a 56‐year chronosequence of plant restoration at decadal intervals in an arid desert region. Bulk soils were separated into silt + clay (<53 μm), fine sand (53–100 μm), and coarse sand (>100 μm) fractions. TOC and TN concentrations of bulk soil and their levels associated with particle size fractions were analyzed. Results showed that plant restoration promoted C and N sequestration in both topsoil and subsoil layers over time, as indicated by elevated levels of OC and N associated with silt + clay and sand fractions. TOC and TN concentrations of 56‐year restored topsoil respectively increased by 31‐ and 43‐fold than did the control (moving dunes); corresponding levels associated with silt + clay or coarse sand fraction respectively increased by more than 30‐ and 20‐fold, whereas less than 15‐fold increases were found in fine sand fraction. In the early stages of plant restoration, both C and N sequestration primarily resulted from finer particle size fractions. In the later stages, increased C sequestration was principally derived from coarse sand fraction, whereas N sequestration was mainly derived from silt + clay fraction. The results highlight that plant restoration stage and soil textural change are key factors leading to divergent soil C and N sequestration in the arid desert region.