Regulation of Nitric Oxide Emissions from Forest and Rangeland Soils of Western North America

Abstract

Nitric oxide (NO) is a relatively short-lived trace gas that reacts with oxygen in the troposphere to produce the air pollutant ozone. It also reacts with water vapor to form nitric and nitrous acids, which acidify precipitation and increase N deposition. Models currently used to predict soil NO fluxes are based on the assumption that NO flux is proportional to the gross rate of nitrification or N mineralization; however, this assumption has not been tested because of the difficulty in measuring gross N-cycling rates in situ. We measured soil NO fluxes, gross and net N-cycling rates, and a variety of other soil characteristics in the forest floor and intact soil cores at nine undisturbed forest and rangeland ecosystems of New Mexico, Utah, and Oregon, USA, to determine which soil variables were most closely related to soil NO flux. Soil NO fluxes ranged from a low of 0.02 ng N·m Ϫ2 ·s Ϫ1 , prior to wetting in a western hemlock-sitka spruce forest on the Oregon coast, to a high of 6.74 ng N·m Ϫ2 ·s Ϫ1 , one hour after soil wetting in a juniper woodland of central Oregon. In contrast to our expectations, neither gross nitrification nor gross mineralization was correlated with soil NO flux. Fluxes were positively correlated with net rates of mineralization and nitrification, soil NO 3 Ϫ concentrations, bulk density, and pH, and negatively correlated with gross rates of NO 3 Ϫ consumption in the forest floor, soil organic carbon (SOC), soil C:N, and soil water content. Principal-component analysis showed that NO flux after water addition (2 cm of water) had a strong negative correlation with microbial demand for N (as indicated by net mineralization, net nitrification, SOC, and C:N). Our results suggest that, even in well-drained soils, NO efflux is limited more by NO consumption than by NO production. As a result, models utilizing the more easily measured net rates, rather than gross rates, may be better predictors of soil NO fluxes across a range of ecosystems.

Changes in Nitrogen-Fixing and Ammonia-Oxidizing Bacterial Communities in Soil of a Mixed Conifer Forest after Wildfire

“…Indeed, autotrophic ammonia oxidation can be a significant source of terrestrial NO and N 2 O (17,49,50), and elevated concentrations of ammonium have been linked to increased rates of NO and N 2 O flux through nitrification (8,38,45,47). Our results suggest that fire-related increases in soil ammonium or pH may influence the structure of the indigenous ammonia-oxidizing community in a mixed conifer forest.…”

Controls on Nitrogen Cycling in Terrestrial Ecosystems: A Synthetic Analysis of Literature Data

“…For instance, ascertaining true rates of nitrification (and consequent denitrification) would seem to be a prerequisite for predicting rates of trace N gas production, one important intersection of N cycling with global climate change. However, efforts to correlate trace gas flux with gross rates of nitrification have met with only mixed success (Davidson et al 1993, Riley and Vitousek 1995, Breuer et al 2002, and net nitrification may be a stronger predictor for trace gas emission than gross nitrification (Stark et al 2002). As an assay for ''plant-available'' inorganic N, the reality of what is available to plants must lie somewhere between net rates and gross rates.…”

Effects of soil rewetting and thawing on soil gas fluxes: a review of current literature and suggestions for future research

“…The magnitude of increased NO flux can be influenced by the duration and severity of antecedent dry periods (ButterbachBahl et al, 2004;McCalley and Sparks, 2008), change in soil moisture (Yienger and Levy, 1995) and temperature (Smart et al, 1999;McCalley and Sparks, 2008), vegetation type (Barger et al, 2005;McCalley and Sparks, 2008), soil type (Martin et al, 2003), microbial demand for N (Stark et al, 2002), frequency of wetting events (Davidson et al, 1991;Hartley and Schlesinger, 2000), previous disturbances (Levine et al, 1988;Poth et al, 1995), and agricultural management (Hutchinson and Brams, 1992). Interestingly, there are conflicting results on the magnitude of increased NO flux after rewetting, which were independent of both the size of rewetting pulse (Davidson, 1992b;Martin et al, 1998) and the periods of antecedent dry days (Martin et al, 1998).…”