Global meta-analysis of terrestrial nitrous oxide emissions and associated functional genes under nitrogen addition.

Functional genes involved in nitrogen (N) cycling regulate soil nitrification, denitrification and N 2 O emissions. However, the general patterns and variability of N functional genes in response to N addition, and their association with N 2 O emission have not been synthesized for terrestrial ecosystems. We synthesized 2068 observations from 144 papers to explore the impact of N addition on the abundance and diversity of N functional genes, and their relationship to N 2 O emissions in croplands, grasslands and forests on a global scale. In croplands, N addition increased N 2 O emissions (109%), the abundance of ammonia-oxidizing archaea (AOA) (19%) , ammonia-oxidizing bacteria (AOB) (95%) , nirK (52%), nirS (40%) and nosZ (41%), and the diversity of AOB (15%), nirS (12%) and nosZ (11%). In grassland, N addition increased AOB abundance (130%) and decreased the abundance of nirS (−99%) and nosZ (−58%) genes, but in forests, significant effects were only found for the abundance of AOA (35%) and AOB (121%). N 2 O emission was negatively correlated with the abundance of nosZ , but positively correlated with the abundance of AOA and AOB. Apart from the abundance of functional AOA, AOB and nosZ genes, climate variables (precipitation and temperature), and available N concentrations were the main factors explaining the variation in N 2 O emission with N addition, as shown by random forest analysis. These findings indicate that impacts on N functional genes that encode enzymes involved in nitrification (AOA, AOB) and in the transformation of N 2 O to N 2 (nos Z) are the main mechanisms behind the effect on N fertilizer-induced N 2 O emissions. • Nitrogen addition increased the abundance of AOA, AOB, nirK , nirS and nosZ. • N 2 O emission was negatively correlated with the abundance of nosZ gene. • N 2 O emission was positively correlated with the AOA and AOB abundance. • AOA, AOB and nosZ abundance were main factors affecting N 2 O emission. • Climate variables and available N concentrations were additional main factors. [ABSTRACT FROM AUTHOR]