Impact of nighttime warming on soil microbial biomass carbon/nitrogen and activity in main winter wheat cropping areas in China

It has been predicted that global climate could warm further with greater increase in daily minimum temperature than in daily maximum temperature. However, little has remained known about the impact of nighttime warming on soil microbial growth and activity. Using the passive nighttime warming (PNW) technique, a 4-year field nighttime warming experiment was conducted during crop-growth periods at the Shijiazhuang, Xuzhou, Xuchang and Zhenjiang sites; covering the main winter wheat cropping regions in China. Soil moisture, soil temperature (0~5 cm), soil microbial biomass and activity were determined under field conditions in 2008-2010. The results showed that nighttime warming significantly decreased soil microbial biomass carbon (C) and nitrogen (N) as well as microbial activity. Compared with the ambient treatment, nighttime warming reduced soil microbial biomass C on average by 11.4%, 7.8%, 10.9% and 8.5%, soil microbial biomass N by 15.2%, 16.7%, 13.8% and 8.4%, and microbial respiration rate by 6.6%, 9.6%, 7.0% and 11.1% at Shijiazhuang, Xuzhou, Xuchang and Zhenjiang sites, respectively. The corresponding soil moisture was 8.8%, 3.7%, 3.8% and 2.9% lower in the warmed plots than in the ambient plots, but all the effects were insignificant. The corresponding temperatures in the 0~5 cm soil layer were higher by 1.2 ℃, 0.7 ℃, 0.7 ℃ and 0.7 ℃ in the warmed plots than in the ambient plots. These results suggest that nighttime warming altered soil C/N cycle and winter wheat growth by influencing soil microbial biomass and microbial activity with certain latitude differences.