Linking Improvement of Soil Structure to Soil Carbon Storage Following Invasion by a C 4 Plant Spartina alterniflora

Coastal wetlands are increasingly recognized as important ecosystems for long-term carbon (C) storage. However, how soil aggregation mediates C accumulation and sequestration in these ecosystems remains unclear. Using the 13C isotope tracer from the invasion of a C4 plant, Spartina alterniflora, into the native ecosystem originally covered by C3 plants across Eastern Chinese coastal wetlands, we investigated a potential C stabilization process via soil structural protection. We quantified changes in soil aggregates, soil organic carbon (SOC), soil total nitrogen (STN), and natural 13C isotope abundance within aggregate fractions across a chronosequence of 0-, 4-, 8-, and 12-year S. alterniflora invasion. Our results showed that soil aggregate stability increased significantly along the chronosequence. Meanwhile, SOC and STN concentrations increased with invasion time in the whole soil and aggregate fractions, which were linked to increasing soil aggregate stability. The contribution of S. alterniflora-derived SOC increased from 18.96 to 40.24% in the 0–20 cm layer and from 4.66 to 32.04% in the 20–40 cm layer across the chronosequence from 4 to 12 years with the highest proportion observed in macro-aggregates. Our results indicate that invasion of S. alterniflora to coastal wetlands can sequester more C largely due to formation and stabilization of soil aggregates by soil structural protection.