The regulation of gross nitrogen transformation rates in greenhouse soil cultivated with cucumber plants under elevated atmospheric [CO2] and increased soil temperature

Climate change scenarios forecast both increase in atmospheric CO2 concentration ([CO2]) and temperature. Elevated [CO2] (e[CO2]) and soil temperature (eST) significantly increased plant growth and nitrogen (N) uptake. However, studies on the combined effect of these factors on soil N transformation and microbial community are scarce in agricultural intensification. In the present work, we cultivated cucumber plants under e[CO2] or/ and eST, followed by a paired labeling 15N tracer experiment (15NH4NO3 and NH415NO3) to quantify soil gross N transformation rates. Results showed that e[CO2] decreased soil gross N nitrification rate, indicated by a decline in ammonia-oxidizing bacteria (amoA-AOB) and nitrite oxidoreductase alpha subunit (nxrA) gene copy numbers, and changed microbial taxonomic composition under ambient soil temperature (aST). Furthermore, eST increased chitinase gene (chiA) and amoA-AOB gene copy numbers and alpha diversity and changed the microbial taxonomic composition to improve soil gross N mineralization and nitrification rates. The combination of e[CO2] and eST promoted soil gross N mineralization, nitrification, and immobilization rates compared with ambient [CO2] and aST. The study showed that the combination of e[CO2] and eST increased the primary gross N transformation rates and accelerated soil N circulation, which could ensure plant N demand. Therefore, combining e[CO2] and eST provided a promising way to help cultivators promote vegetable growth in winter, mitigate soil N loss, and achieve sustainable development in greenhouse vegetable cultivation.