Effects of aggregates size and glucose addition on soil organic carbon mineralization and Q10 values under wide temperature change conditions

- SOC mineralization in 1-2 mm aggregates was higher than that in other size classes.
- Glucose could break the restrain effect of high temperature to SOC mineralization.
- Both high temperature and low amount of glucose addition reduced Q10 values.
- The main source of soil CO2 emission was from <1 mm aggregates in steppe of China.

Soil organic carbon mineralization (SOCmin) plays an important role in soil carbon (C) cycling in terrestrial ecosystems. The contribution of soil aggregates (Sa) to SOCmin and the effects of glucose addition on temperature sensitivity of SOCmin (Q10) are not clear. A laboratory incubation experiment has been set to examine the SOCmin of Sa by changing the soil temperature and adding glucose. The undisturbed soil samples (CK) were separated into four aggregate size fractions (<0.25, 0.25-1, 1-2 and 2-4 mm diameter) using a dry sieving procedure. The resulted showed that SOCmin in the 1-2 mm aggregates were higher than that in other size of aggregates. Q10 values of 0.25-1 mm aggregates were significantly higher than that in other size classes (P < 0.05) in 10-30 °C range. However, In 30-50 °C range, the Q10 values of 1-2 mm aggregates were significantly higher than that in other size classes (P < 0.05). The addition of glucose in soil could break the restrain effect of high temperature on SOCmin. However, glucose addition significantly reduced the Q10 values in 10-30 °C range (P < 0.05). Although 1-2 mm aggregates could generate a positive feedback for temperature change in CO2 production, this aggregates were not the main CO2 emission source because of the low aggregates ratio (5.76%). The <1 mm aggregates in our incubation conditions were the main CO2 emission source because of their high aggregates ratio (80.35%) in soil.

Principal component analysis (PCA) graph of SOCmin among the aggregates size, temperature change and glucose addition treatments. The SOCmin in the 1-2 mm aggregates were higher than that in other size of aggregates. The increase rate of SOCmin in no glucose addition treatment was lower than that in glucose addition treatment, implying the low amount of added glucose decreased Q10 value.244