We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Dynamic Controls on Field‐Scale Soil Nitrous Oxide Hot Spots and Hot Moments Across a Microtopographic Gradient.
- Authors
Krichels, Alexander H.; Yang, Wendy H.
- Abstract
Soil nitrous oxide (N2O) emissions are highly variable in space and time, making it difficult to estimate ecosystem level fluxes of this potent greenhouse gas. While topographic depressions are often evoked as permanent N2O hot spots and rain events are well‐known triggers of N2O hot moments, soil N2O emissions are still poorly predicted. Thus, the objective of this study was to determine how to best use topography and rain events as variables to predict soil N2O emissions at the field scale. We measured soil N2O emissions 11 times over the course of one growing season from 65 locations within an agricultural field exhibiting microtopography. We found that the topographic indices best predicting soil N2O emissions varied by date, with soil properties as consistently poor predictors. Large rain events (>30 mm) led to an N2O hot moment only in the early summer and not in the cool spring or later in the summer when crops were at peak growth and likely had high evapotranspiration rates. In a laboratory experiment, we demonstrated that low heterotrophic respiration rates at cold temperatures slowly depleted soil dissolved O2, thus suppressing denitrification over the 2–3 day timescale typical of field ponding. Our findings show that topographic depressions do not consistently act as N2O hot spots and that rainfall does not consistently trigger N2O hot moments. We assert that the spatiotemporal variation in soil N2O emissions is not always characterized by predictable hot spots or hot moments and that controls on this variation change depending on environmental conditions. Plain Language Summary: Soils are the primary source of nitrous oxide (N2O), a greenhouse gas that contributes to global warming. Nitrous oxide is produced under oxygen‐depleted conditions that can occur when soils are saturated with water. Large rain events are therefore thought to lead to short periods of high soil N2O emissions. Landscape topography can shape spatial patterns in soil moisture and other soil properties that may regulate spatial variation in soil N2O emissions. The goals of this study were to determine which topographic factors best predict spatial variation in soil N2O emissions and under what conditions, and to determine when large rain events may not lead to bursts of soil N2O emissions. We found that throughout the growing season, all topographic indices were poor predictors of soil N2O emissions in an agricultural field. A large early summer rain event triggered a pulse of soil N2O emissions, but large rain events did not trigger similar pulses in the cool spring months or later in the summer when the crops were at peak growth with high soil water demand. This has important implications for predicting how soil N2O emissions will respond to expected future changes in temperature and rainfall, feeding back on climate change. Key Points: Topographic depressions did not consistently act as nitrous oxide hot spots, with controls on fluxes varying over the growing seasonCold spring temperatures limit soil respiration that depletes dissolved oxygen to induce nitrous oxide production by denitrificationLarge summer rainfall events may not stimulate soil nitrous oxide emissions, even from topographic depressions, when soil moisture is low
- Subjects
NITROUS oxide &; the environment; GREENHOUSE gases; TOPOGRAPHY; CROP growth; EVAPOTRANSPIRATION
- Publication
Journal of Geophysical Research. Biogeosciences, 2019, Vol 124, Issue 11, p3618
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2019JG005224