Response of soil aggregate stability and distribution of organic carbon to alpine grassland degradation in Northwest Sichuan

Soil aggregate stability and the distribution of organic carbon in different aggregate fractions would be affected by alpine grassland degradation. We investigated the aggregate stability by mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (D), and the distribution and storage of soil organic carbon (SOC) in different sized aggregates of degraded alpine grassland soils in northwest Sichuan of China. Results showed that the MWDs and GMDs of soil aggregates with different degradation degrees were significantly lower than those of non-degraded grassland (P < .05), and the D (2.613–2.673) of degraded grasslands was significantly higher than that of non-degraded grassland (2.487–2.516) (P < .05). Soil aggregates organic carbon tended to increase first and then decrease with the decrease of particle size of aggregates. The highest SOC was found in larger aggregates (0.5–2 mm), followed by those in smaller aggregates (0.25–0.5 mm), macroaggregates (>2 mm) and microaggregates (<0.25 mm). Overall, the study found that the organic carbon storage of soil aggregates in degraded grasslands existed mainly in the microaggregates (<0.25 mm), indicating that the microaggregates were able to protect the SOC from decomposition. This study provides scientific basis for the optimal management of the soil carbon pool in alpine grassland.