Influence of organic matter input and temperature change on soil aggregate-associated respiration and microbial carbon use efficiency in alpine agricultural soils

Understanding the dynamics of soil respiration, microbial carbon use efficiency (CUE), and temperature sensitivity (Q10) in response to exogenous organic matter (EOM) input, soil aggregate size, and incubation temperature is crucial for predicting soil carbon cycling responses to environmental changes. In this study, these interactions were investigated by 180-day incubation of soil aggregates supplemented with EOM at various temperatures (5°C, 15°C and 25°C). The results reveal an ‘L-shaped’ trend in soil respiration on the time scale across all treatments, characterized by initial rapid declines followed by stability. EOM input and higher temperatures significantly enhance respiration rates. Notably, the respiratory rates of soil aggregates of different sizes exhibit distinct patterns based on the presence or absence of EOM. Under conditions without the addition of EOM, larger aggregates show relatively lower respiration rates. Conversely, in the presence of EOM, larger aggregates exhibit higher respiratory rates. Furthermore, Q10 decreases with increasing aggregate size. The relationship between Q10 and the substrate quality index (SQI) supports the carbon quality temperature (CQT) hypothesis, highlighting SQI’s influence on Q10 values, particularly during later incubation stages. Microbial CUE decreases with EOM input and rising temperatures. Meanwhile, aggregate size plays a role in microbial CUE, with smaller aggregates exhibiting higher CUE due to enhanced nutrient availability. In conclusion, the intricate interplay of EOM input, aggregate size, and temperature significantly shapes soil respiration, microbial CUE, and Q10. These findings underscore the complexity of these interactions and their importance in modeling soil carbon dynamics under changing environmental conditions.