Land use type shapes carbon pathways in Tibetan alpine ecosystems: Characterization of 13C abundance in aggregates and density fractions

• Plantation on the Tibetan Plateau reduces PAD and slows carbon transfer. • Aggregate differentiation of organic carbon exists in density fractions but not SOC. • Aggregate differentiation in δ 13 C and Δ 13 C in density fractions of only plantation. • The direction of δ 13 C enrichment from LF to PF to MF indicates carbon transfer in alpine plantation. Insight into carbon turnover in soil aggregates and density fractions is essential to reduce uncertainty in estimating carbon pools on the Tibetan Plateau. Further, how these vary with land-use type is unclear. In this study, the effect of land use type on carbon storage and fractionation based on organic carbon and its 13 C abundance was quantified at the microscale of soil aggregates and density fractions in Tibetan alpine. The sequence of soil aggregates destruction in plantation (13.1%)<shrubland (32.7%)<grassland (47.9%) farmland (61.8%) shows that plantation strengthen soil structure. Plantation increased light fraction organic carbon (28.3%) but reduced mineral associated organic carbon (40.6%) contribution to carbon stock compared to farmland (13.5%, 70.3%). Interestingly, plantation enhanced aggregational differentiation of organic carbon and 13 C in each density fraction, whereas no such phenomenon exists in soil organic carbon. Carbon isotope analyses revealed that carbon transfer in the plantation occurred from light fraction in macroaggregate (-24.9‰) to the mineral associated fraction in microaggregate (-19.9‰). When compared to the other three land-use types, the low transferability of carbon in aggregates and density fractions in plantation provides a stable carbon pool for the Tibetan Plateau. This study shows that plantation can mitigate global climate change by slowing carbon transfer and increasing carbon storage at the micro-scale of aggregates and density fractions in alpine regions.