Insight into the carbon turnover in soil aggregates and density fractions is essential for reducing the uncertainty in estimating carbon pools on the Tibetan Plateau, and how they vary with land use type is unclear. In this study, the effect of land use type on carbon storage and fractionation was quantified based on organic carbon and its ¹³C abundance at the microscale of soil aggregates and density fractions in Tibetan alpine ecosystems. The sequence of soil aggregate destruction in the land use types of plantation (13.1%)<shrubland (32.7%)<grassland (47.9%)<farmland (61.8%) shows that plantations strengthen the soil structure. Plantation land had a greater contribution of light fraction organic carbon (28.3%) but a lower contribution of mineral-associated organic carbon (40.6%) to the carbon stock compared to farmland (13.5 and 70.3%). Interestingly, plantation land enhanced the aggregational differentiation of organic carbon and ¹³C in each density fraction, whereas no such phenomenon existed in the soil organic carbon. Carbon isotope analyses revealed that carbon transfer in the plantation land occurred from the light fraction in macroaggregates (–24.9‰) to the mineral-associated fraction in microaggregates (–19.9‰). When compared to the other three land use types, the low transferability of carbon in aggregates and density fractions in plantation land provides a stable carbon pool for the Tibetan Plateau. This study shows that plantations can mitigate global climate change by slowing carbon transfer and increasing carbon storage at the microscale of aggregates and density fractions in alpine regions.

floodplain wetland  /  soil organic carbon  /  spatial pattern  /  dynamic change