Ecological Restoration Enhances the Stability and Associated Organic Carbon of Soil Aggregates in a Tibetan Alpine Meadow

ABSTRACT Fencing and reseeding are two widely implemented ecological restoration strategies aimed at rehabilitating degraded grasslands globally. However, their effects on soil aggregates have been insufficiently explored. Employing the space‐for‐time substitution approach, we collected intact soils from a degraded alpine meadow, a fenced alpine meadow (natural restoration), a reseeded alpine meadow (interventional restoration), and an undegraded alpine meadow on the eastern Tibetan Plateau. Our main objective was to assess how the composition, stability, and associated organic carbon content of soil water‐stable aggregates responded to a 12‐year restoration effort in degraded alpine meadows. The results revealed that both restoration measures enhanced plant biomass, the levels of soil carbon, nitrogen, and phosphorus, as well as the concentrations of microbial phospholipid fatty acids. In contrast, these measures had a minimal effect on soil bulk density and glomalin‐related soil protein, while causing a reduction in soil pH. Post‐restoration, the mass proportion of macroaggregates increased notably by 66.45%–71.18%, whereas that of microaggregates and silt‐clay particles exhibited decreasing trends. The mean weight diameter and geometric mean diameter of the aggregates also significantly enhanced following restoration, indicating improvements in soil structural health and stability. However, the restored paddocks still showed lower aggregate stability than the undegraded paddock, suggesting that a longer restoration period may be required to fully recover the degraded soil structure. The aggregate‐associated organic carbon content significantly increased after reseeding but showed a negligible response to fencing alone. Nevertheless, both restoration measures improved the organic carbon stock within macroaggregates and its contribution to soil total organic carbon. Soil pH, total nitrogen content, and plant biomass were identified as key factors influencing the composition and associated organic carbon content of aggregates during restoration. Our findings indicate that ecological restoration enhances the stability and associated organic carbon accumulation of soil aggregates, primarily by promoting the formation of macroaggregates in degraded alpine meadows on the Tibetan Plateau.