Straw Addition and Low Soil Moisture Decreased Temperature Sensitivity and Activation Energy of Soil Organic Matter

Straw incorporation into soils is an effective and low-cost approach to sequester organic carbon (C) and improve soil quality. However, the interactive effects of soil moisture and temperature on soil organic matter (SOM) mineralization were unclear in the presence of plant residues. We evaluated influences of 13C 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°C or 22°C) by an experiment incubation. Without straw addition, CO2 production at 22°C was 2-3 times more than at 12°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 at all temperature and moisture levels resulting in positive priming effect (PE), with the highest PE in 45% WHC at 22℃ in both soils. Temperature sensitivity (Q10 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°C and DOC/SOC) compared with control (no straw addition). The Q10 values of SOM and straw decomposition was higher at 65% WHC compared to 45% WHC, implying that the drought condition has potential to dampen effects of temperature on the decomposition. We also found the Q10 was positively correlated with activation energy and negatively with soil C quality, which supporting the C quality–temperature hypothesis. Summarizing, our findings contribute to the better understanding of soil C dynamic response to exogenous C input under environment change.