Pathways and controls of N2O production in greenhouse vegetable production soils

Here, the combined approaches of a N-15 tracing technique, DNA and mRNA analyses, and modeling were used to investigate the mechanisms underlying rapid nitrate (NO3-) accumulation and identify the relative contributions of autotrophic nitrification, heterotrophic nitrification, codenitrification, and denitrification to nitrous oxide (N2O) production in six vegetable soils. The soil pH had a positive effect on the NO3- retention capacity (p<0.01) and a negative effect on the net NO3- production rate (p<0.05), resulting in higher NO3- accumulation in acidic soils. Meanwhile, autotrophic nitrification accounted for 39-86% of N2O production in alkaline soils, whereas denitrification was responsible for 85% of N2O production in acidic soils. The results of structural equation modeling indicated that autotrophic nitrification-derived N2O production was influenced by soil C/N ratio, the gross NO3- production rate, and the ammonia-oxidizing archaea (AOA) amoA/ammonia-oxidizing bacteria (AOB) amoA mRNA ratio, while denitrification-derived N2O production was influenced by pH, the gross NO3- consumption rate, and the abundance of nirS mRNA, all of which were influenced directly and indirectly by in situ climate parameters of mean annual precipitation and mean annual temperature. Furthermore, regression analyses revealed that the soil total N content affected heterotrophic nitrification- and the pH affected codenitrification-derived N2O production, which contributed 9-76% and 0-7%, respectively, to the total N2O production in vegetable soils. The current findings improve our understanding of the mechanisms of NO3- buildup and N2O stimulation in intensively managed agricultural ecosystems.