Nitrification is a minor source of nitrous oxide (N₂O) in an agricultural landscape and declines with increasing management intensity

Abstract

Nitrous oxide (N 2 O) is a potent greenhouse gas with a 100-year global warming potential ~300 times higher than CO 2 , and has the third largest radiative forcing among the biogenic greenhouse gases (Myhre et al., 2013). N 2 O also depletes stratospheric ozone (Revell et al., 2012). Globally, soils are the dominant sources of both anthropogenic and natural emissions of N 2 O, with 1.7-4.8 Tg N 2 O-N year −1 emitted by agricultural soils and 3.3-9.0 Tg N 2 O-N year −1 from soils under natural vegetation (Ciais et al., 2013). Ammonia (NH 3 ) oxidation, the rate-limiting step of nitrification, is performed in soil mainly by aerobic ammonia-oxidizing bacteria

In Silico Evaluation of Plant Nitrification Suppression Effects on Agroecosystem Nitrogen Loss

“…This is largely due to the predicted role of nitrification as the dominant N 2 O source at our site and the source of NO 3 - for denitrification. Our model experiments show that nitrification is responsible for 78% of annual soil N 2 O emissions, consistent with some empirical studies in cropping systems (Skiba et al 1993, Bremner 1997, Stevens et al 1997, Toyoda et al 2011, Tierling and Kuhlmann 2018) but inconsistent with other empirical studies showing denitrification as the dominant N 2 O source (Müller et al 2014, Li et al 2016, Liang and Robertson 2021). In particular, nitrification appears to be a significant source of N 2 O when NH 4 + substrate is abundant and soils are not fully saturated (Bremner 1997, Toyoda et al 2011), which is consistent with the significant increase in both gross nitrification and N 2 O emissions after fertilization in our study.…”

Reactive nitrogen restructures and weakens microbial controls of soil N2O emissions

“…We also noted that a single and frequently occurring OTU of an ammonia-oxidizing bacteria ( Nitrosospira ) increased with fertilization. Since they can produce N 2 O, this could potentially add to elevated in situ emissions from fertilized soils, and recent work suggests that ammonia oxidation likely contributes 0.1–10% of possible maximum N 2 O emission rates 10 . Overall, the observed shifts underscore that traits that determine how the microbial community responds to elevated N r inputs occur at different phylogenetic scales amongst community members, and are not necessarily inferred from taxonomic affiliation.…”

“…Microbial communities that perform denitrification are the predominant source of N 2 O in arable soils 8 – 10 . Denitrifying communities remove up to 56% of newly fixed N r annually at the global scale and ~8% of the total denitrification flux results in N 2 O 8 .…”

Arbuscular Mycorrhizae Shift Community Composition of N-Cycling Microbes and Suppress Soil N2O Emission

“…Although N 2 O is generated mainly by soil nitrifiers and denitrifiers, microbial communities that perform denitrification in general play a dominant role in soil N 2 O emissions, particularly in agricultural soil (also see Supplementary Materials and Methods for more details). 9,10 While chemical N to the conventional soil only provides N substrate, organic manures introduce both C and N substrates for denitrifiers. 71−73 Denitrifiers are predominantly heterotrophic bacteria that require energy from organic matter to convert NO 3 − to N 2 O.…”

“…5−7 Two microbial processes, nitrification and denitrification, are primary sources of N 2 O emissions, 4,5,8 but denitrification is the predominant source of N 2 O from agricultural soils. 9,10 In denitrification, denitrifying microbes produce various reductases that convert nitrogen oxides (NO 3 − , NO 2 − ) into gaseous products (i.e., N 2 O and N 2 ). 8,11 Because denitrifier communities are highly diverse and difficult to quantify, the functional genes that encode reductases have been widely used to characterize the denitrifier communities.…”