Soil salinity changes the temperature sensitivity of soil carbon dioxide and nitrous oxide emissions

Soil salinization largely affects greenhouse gas emissions from soils, but its effects on the temperature sensitivity (Q(10)) of soil carbon dioxide (CO2) emissions and nitrous oxide (N2O) emissions remain unclear. In this study, a temperature-controlled (15 degrees C and 25 degrees C) microcosm experiment was performed for 56 days to evaluate the effects of soil salinity (0.1%, 0.3%, 0.6% and 1.0% salt contents) on the Q(10) of CO2 emissions, N2O emissions and phospholipid fatty acid (PLFA)-distinguishable microbial communities in sandy clay loam (SCL) soil and silty clay (SC) soil. In both soils, soil salinity inhibited soil microbial respiration under both temperature conditions. However, soil salinity significantly (p < 0.05) enhanced the temperature sensitivity of soil CO2 emissions, indicating that although soil salinization inhibited CO2 production in the soil, more CO2 would be produced in the salinized soils under the warming scenario. Increasing soil salinity simulates the release of N2O in both soils, whereas the effects of soil salinity on the Q(10) of soil N2O emissions differed between the two soils. There was no significant (p > 0.05) difference in the Q(10) of soil N2O emissions among the four salinity levels in the SCL soil, but soil salinization significantly (p < 0.05) increased the Q(10) of the SC soil. The relative changes in soil ammonium (NH4+)-nitrogen (N) at 15-25 degrees C and the temperature sensitivity of Gram-positive bacteria and fungi were negatively (p < 0.05) related to the Q(10) of soil CO2 emissions. The Q(10) of soil N2O was positively (p < 0.05) correlated with the relative changes in soil nitrate (NO3-)-N at 15-25 degrees C. Overall, our results highlight the important role of soil salinity in controlling the temperature sensitivity of soil CO2 and N2O emissions, and soil salinization likely causes a high risk of soil greenhouse gas emissions under climate warming conditions.