Short-term effects of asymmetric day and night warming on soil N2O, CO2 and CH4 emissions: A field experiment with an invasive and native plant

Global warming and biological invasion are the main aspects of global change. Understanding the effects of warming on soil greenhouse gas (GHG) emissions represents a challenge to comprehending the feedbacks associated with climate change. Asymmetric warming due to the greater warming during the night than during the day leads to decreased diurnal temperature range (DTR) which have lasted for several decades and are projected to continue over this century. However, few experimental studies have attempted to integrate the asymmetric warming and plant invasion with soil GHG emissions. A two-factor (warming and plants) field experiment was conducted herein using infrared heaters to increase temperatures. We set four warming treat-ments (no warming, symmetric warming, asymmetric warming with increased and decreased DTR) and three plant treatments (bare soil without plants, the invasive species Bidens alba, native species Eleusine indica). We found warming with decreased DTR induced higher nitrous oxide (N2O) emissions in the bare soil and with E. indica than symmetric warming at the early stage of warming, whereas such effects diminished with warming duration. In general, no significant differences in soil methane (CH4) or carbon dioxide (CO2) emissions were found between the symmetric and asymmetric warming. The observed different effects on soil GHG emissions between E. indica and B. alba were mainly due to altered soil nitrate (NO3-) and ammonia (NH4+) content resulted from their growth. Redundancy analysis indicated that soil NO3_ NH4+ and the functional gene nirS were the main factors driving the variance in soil GHG emissions, while soil pH and NO3- were the main driving factors of functional genes abundances. Overall, this study highlights the importance of effects of asymmetric day/night warming on soil GHG emissions associated with plant invasion.