Straw addition and low soil moisture decreased temperature sensitivity and activation energy of soil organic matter

Incorporating straw into soils is an effective and cost-efficient method for sequestering organic carbon (C) and enhancing soil quality. However, the interactive effects of soil moisture and temperature on soil organic matter (SOM) mineralization have remained unclear in the presence of plant residues. We assessed the impacts of C-13-labeled maize (Zea mays) straw on SOM mineralization in two soils with contrasting soil C content (3.0 % and 6.8 %) under two moisture levels (45 % or 65 % water holding capacity (WHC)) and two temperatures (12 degrees C or 22 degrees C) through an experimental incubation. In the absence of straw addition, CO2 production at 22 degrees C was 2-3 times more than at 12 degrees C, and was 31-40 % higher at 65 % WHC than at 45 % WHC in both soils. Soil temperature and moisture interactively affected straw decomposition. After a 66-day incubation, approximately 7-11 % of straw was decomposed to CO2, contributing 44-67 % to the total CO2 production. Straw addition increased SOM mineralization across all temperature and moisture levels, resulting in a positive priming effect (PE). The highest PE was observed at 45 % WHC and 22degree celsius in both soils. The temperature sensitivity (Q(10) value) of native SOM mineralization decreased with straw addition due to higher quality SOM (i.e., higher the basal microbial respiration rate per unit organic C at 0 degrees C and DOC/SOC) compared with control (no straw addition). The Q(10) values of SOM and straw decomposition was higher at 65 % WHC compared to 45 % WHC, indicating that drought conditions have potential to dampen effects of temperature on the decomposition. We also discovered a positive correlation between Q(10) and activation energy and a negative correlation with soil C quality, providing support for the C quality temperature hypothesis. In summary, our findings contribute to advancing our understanding of how soil C dynamics respond to exogenous C inputs under environment change.