Soil organic carbon (SOC) formation and mineralization play critical roles in soil biogeochemical cycling and global climate regulation. Understanding the differences in SOC composition among aggregates is crucial for interpreting the C stabilization pathway through the δ13C approach. However, it remains largely unknown how land use changes influence long-term C flow and sequestration in karst ecosystems.
In a study published in Catena, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences (CAS) applied space-for-time substitution and natural 13C abundance approaches to explore how land use changes in karst ecosystems influenced soil organic carbon and carbon flow pathways.
The study was conducted in the Stone Forest World Geo-Park, Shilin County, Yunnan.
The researchers compared soil samples under four land use types (farmland, grassland, shrubland and forestland) to analyze the soil aggregate stability, labile and recalcitrant SOC stocks and carbon flow paths between them.
They found that land-use conversion and soil depth significantly influenced soil aggregate distribution, aggregate-associated organic carbon fractions, stocks, and carbon stabilization pathways in the Shilin karst area. Forestland had the highest SOC stock in topsoil soil, followed by grassland, shrubland, and cropland. Across the entire soil profile, the shrubland and cropland had lower SOC stocks than other types of land use.
Macroaggregates were identified as the primary contributors to SOC across all land uses. Soil aggregate-associated C flow pathways predominantly occurred from macroaggregates to microaggregates and silt + clay size classes. The δ13C was enriched as aggregate size decreased. The transition from grassland to forestland was associated with a decrease in the δ13C of bulk soil, indicating reduced SOC decomposition and improved soil stability.
The results highlighted that long-term soil labile and recalcitrant organic C pools and C stabilization mechanisms at aggregate level are largely affected by land use. Agricultural cultivation induced higher carbon turnover rates and carbon losses, while grassland and forest restoration helped to increase the stock of soil organic carbon, especially stable SOC in the form of aggregates.
The researchers thus suggested that appropriate land management strategies, such as grassland and forest restoration, are effective ways to enhance SOC sequestration in karst regions.
Published: 28 December 2024
