Acidity and organic matter promote abiotic nitric oxide production in drying soils

Abstract

Soils are an important source of NO, particularly in dry lands because of trade-offs that develop between biotic and abiotic NO-producing processes when soils dry out. Understanding how drier climates may offset the balance of these trade-offs as soils transition toward more arid states is, therefore, critical to estimating global NO budgets, especially because drylands are expected to increase in size. We measured NO emission pulses after wetting soils from similar lithologies along an altitudinal gradient in the Sierra Nevada, CA, where mean annual precipitation varied from 670 to 1500 mm. Along the gradient, we measured field NO emissions, and used chloroform in the laboratory to reduce microbial activity and partition between biotic and abiotic NO-producing processes (i.e., chemodenitrification). Field NO emission pulses were lowest in the acidic and SOM-rich soils (4-72 ng NO-N m s ), but were highest in the high-elevation barren site (~560 ng NO-N m s ). In the laboratory, NO emission pulses were up to 19× greater in chloroform-treated soils than in the controls, and these abiotic pulses increased with elevation as pH decreased (6.2-4.4) and soil organic matter (SOM) increased (18-157 mg C g ). Drought can shift the balance between the biotic and abiotic processes that produce NO, favoring chemodenitrification during periods when biological processes become stressed. Acidic and SOM-rich soils, which typically develop under mesic conditions, are most vulnerable to N loss via NO as interactions between pH, SOM, and drought stimulate chemodenitrification.

Isotopic Composition of In Situ Soil NOx Emissions in Manure‐Fertilized Cropland

“…We also investigate the potential role of abiotic NO production via chemodenitrification of NO 2 − . Although our bulk soil pH (~6.2) is higher than acidic conditions favoring chemodenitrification at pH <5.5, there is a potential for acidic microsites where this process can occur on mineral surfaces with reduced metals such as Fe III (Heil et al, ; Howyak et al, 2016; Homyak et al, ). However, the isotope effect associated with NO production via chemodenitrification is unknown.…”

“…Moist soils are generally assumed to have low NO 2 − availability since NO 2 − is rapidly consumed during both nitrification and denitrification. However, high NO 2 − levels in moist, near neutral pH soils have recently been observed (Homyak et al, , ). Therefore, the slightly acidic (pH ~ 6.2), relatively moist soils during this study likely promote conditions favoring a combination of biotic and abiotic NO production, especially for treatments with lower denitrification rates.…”

Genome-Scale, Constraint-Based Modeling of Nitrogen Oxide Fluxes during Coculture of Nitrosomonas europaea and Nitrobacter winogradskyi

“…Abiotic reactions can have a profound effect in environmental systems, and modeling efforts in these systems will need to take these reactions into account. For example, both abiotic and biotic factors are important for NO and N 2 O production in drying soils, particularly in the face of a potentially warming climate (5, 49). Another important factor influencing N 2 O production in environmental systems are gas diffusion constraints (50).…”

Nitrogen Transformations Associated with N2O Emissions in Agricultural Soils

“…As have been reported by previous studies, factors impacting nitriication process including quantity and quality of soil N input, soil moisture (water holding capacity) [34,35], soil temperature [10,17,30], irrigation and tillage practices, soil type, soil oxygen concentration, dissolved organic C availability (controlling substrate availability of soil microbes) [17,36], additives for soil Nitrogen in Agriculture -Updatesamelioration, vegetation or crop types [37], land use change and soil pH [36,38]. While soil N provided substrate for transformation process producing soil N 2 O, other factors regulated N 2 O production process mainly via indirect efects on soil microbial activities.…”