Warmer and drier conditions alter the nitrifier and denitrifier communities and reduce N2O emissions in fertilized vegetable soils

Nitrous oxide (N2O) is a potent greenhouse gas and is mainly produced from agricultural soils especially vegetable soils with large N fertilizer input. How future projected climate change may impact on the N2O emissions and the related key (de)nitrifier communities in such ecosystem is poorly understood. The aim of this field study was to determine the interactive effects of a simulated warmer and drier climate on (de)nitrifier communities and N2O emissions in a vegetable soil. A warmer (+3.3 °C) and drier climate (−14.4% soil moisture content) was created with greenhouses with or without urea N fertilizer application. The variation of microbial population abundance and community structure of Ammonia-oxidizing archaea (AOA), bacteria (AOB) and denitrifiers (nirK/S, nosZ) were determined using Real time-PCR and sequencing. The results showed a strong interactive effect of simulated climate change with N fertilizer applications, whereby the impacts of warmer and drier conditions on the microbial communities and N2O emissions were more evident when N fertilizer was applied. The simulated warmer and drier conditions in the greenhouses significantly decreased N2O emissions largely due to the drier soil conditions. The abundance and community structure of AOB showed more rapid responses than AOA under the simulated climate conditions when N fertilizer was applied. Changes of AOB community structure were significantly correlated with soil moisture content and NH4+-N concentration. The simulated climate change did not affect the nirS gene abundance, but significantly increased nirK gene abundance, and significantly decreased nosZ gene abundance with urea application. N2O emissions were positively correlated with the bacterial amoA abundance and with the ratio of nirK/nosZ gene abundance. Therefore, bacterial amoA, nirK- and nosZ-type denitrifiers are the dominant microbial communities which were affected by the simulated climate conditions and are thus critically important for N cycling in vegetable soils under a changing climate.