Rapid nitrate reduction produces pulsed NO and N2O emissions following wetting of dryland soils

Abstract

Soil drying and wetting cycles can produce pulses of nitric oxide (NO) and nitrous oxide (N2O) emissions with substantial effects on both regional air quality and Earth’s climate. While pulsed production of N emissions is ubiquitous across ecosystems, the processes governing pulse magnitude and timing remain unclear. We studied the processes producing pulsed NO and N2O emissions at two contrasting drylands, desert and chaparral, where despite the hot and dry conditions known to limit biological processes, some of the highest NO and N2O flux rates have been measured. We measured N2O and NO emissions every 30 min for 24 h after wetting soils with isotopically-enriched nitrate and ammonium solutions to determine production pathways and their timing. Nitrate was reduced to N2O within 15 min of wetting, with emissions exceeding 1000 ng N–N2O m−2 s−1 and returning to background levels within four hours, but the pulse magnitude did not increase in proportion to the amount of ammonium or nitrate added. In contrast to N2O, NO was emitted over 24 h and increased in proportion to ammonium addition, exceeding 600 ng N–NO m−2 s−1 in desert and chaparral soils. Isotope tracers suggest that both ammonia oxidation and nitrate reduction produced NO. Taken together, our measurements demonstrate that nitrate can be reduced within minutes of wetting summer-dry desert soils to produce large N2O emission pulses and that multiple processes contribute to long-lasting NO emissions. These mechanisms represent substantial pathways of ecosystem N loss that also contribute to regional air quality and global climate dynamics.

Biogeochemical and ecosystem properties in three adjacent semi‐arid grasslands are resistant to nitrogen deposition but sensitive to edaphic variability

“…In contrast to ion exchange resin data, there were no increases in N 2 O or NO x efflux rates within 90 days of the high N treatment addition in March 2013 (Figure 1b). Gaseous N loss is often considered a dominant pathway of N loss from deserts in the southwestern U.S. (Peterjohn & Schlesinger, 1990), with a significant proportion being attributed to abiotic gas production resulting from the time‐sensitive, pulsed re‐wetting of dry soils (as opposed to microbial processing alone; McCalley & Sparks, 2009, Homyak et al, 2016, Krichels et al, 2022). Although we added 3 mm of water along with our N treatments prior to each gas sampling event, it is possible that our sampling schedule failed to capture large N gas flux events.…”

Precipitation legacies amplify ecosystem nitrogen losses from nitric oxide emissions in a Pinyon–Juniper dryland

“…Since baseline winter precipitation (189 mm) was only slightly higher than normal (154 mm historical average), it is possible that wetter winters-and associated larger water additions to the Winter+ plots-are necessary to further stimulate carryovers of microbial biomass. Although nitrifying microorganisms are thought to produce NO in drylands (Homyak et al, 2016;Krichels et al, 2022), we also did not observe a treatment effect on the size of archaeal or bacterial nitrifier communities (Appendix S1: Figure S4). Rather, greater microbial biomass may have enhanced inorganic N supply via rapid N mineralization following wetting, or stimulated conversion of N to NO via microbial denitrification (Austin et al, 2004).…”

“…In contrast to dry soils, moist soils maintain active biological sinks for N, limiting N losses via NO (Homyak et al, 2016; McCulley et al, 2009). As such, rainfall‐induced drying‐rewetting cycles represent critical periods when a substantial fraction of ecosystem N inputs can be transferred to the atmosphere as NO (Eberwein et al, 2020; Krichels et al, 2022; Soper et al, 2016). However, it is not well established whether the magnitude of NO pulses vary as a function of the legacies of past precipitation.…”

Soil water status shapes nutrient cycling in agroecosystems from micrometer to landscape scales

“…Also, the frequently observed flush of NO and N 2 O emissions after rewetting of dry soil has been attributed to a concerted action of a very fast abiotic mechanism, so‐called chemodenitrification, and has been found to substantially contribute to total N 2 O and NO emissions from soils in a recent meta‐analysis (Wei et al., 2022). This process is responsible for the rapid release of NO and N 2 O within minutes after rewetting, whereas the microbiological processes of nitrification and denitrification act over a few hours up to a few days (Harris et al., 2021; Homyak et al., 2017; Krichels et al., 2022).…”