Microbial mechanisms and ecosystem flux estimation for aerobic NO _y emissions from deciduous forest soils

Abstract

Reactive nitrogen oxides (NOy; NOy= NO + NO2+ HONO) decrease air quality and impact radiative forcing, yet the factors responsible for their emission from nonpoint sources (i.e., soils) remain poorly understood. We investigated the factors that control the production of aerobic NOyin forest soils using molecular techniques, process-based assays, and inhibitor experiments. We subsequently used these data to identify hotspots for gas emissions across forests of the eastern United States. Here, we show that nitrogen oxide soil emissions are mediated by microbial community structure (e.g., ammonium oxidizer abundances), soil chemical characteristics (pH and C:N), and nitrogen (N) transformation rates (net nitrification). We find that, while nitrification rates are controlled primarily by chemoautotrophic ammonia-oxidizing archaea (AOA), the production of NOyis mediated in large part by chemoautotrophic ammonia-oxidizing bacteria (AOB). Variation in nitrification rates and nitrogen oxide emissions tracked variation in forest communities, as stands dominated by arbuscular mycorrhizal (AM) trees had greater N transformation rates and NOyfluxes than stands dominated by ectomycorrhizal (ECM) trees. Given mapped distributions of AM and ECM trees from 78,000 forest inventory plots, we estimate that broadleaf forests of the Midwest and the eastern United States as well as the Mississippi River corridor may be considered hotspots of biogenic NOyemissions. Together, our results greatly improve our understanding of NOyfluxes from forests, which should lead to improved predictions about the atmospheric consequences of tree species shifts owing to land management and climate change.

Hotspots of nitrogen deposition in the world's urban areas: a global data synthesis

“…For example, two-thirds of forest plots measured across Europe in one study exceeded critical loads for N inputs (Lorenz and Granke 2009); likewise, in an unrelated investigation, rates of N deposition across the US were associated with declining plant species richness in both forested and non-forested ecosystems (Simkin et al 2016). Elevated N deposition has also been associated with increased soil acidification in both rural (van Breemen et al 1984;Lu et al 2014) and urban (Huang et al 2015) areas, eutrophication of waterways , and elevated emissions of climate-forcing greenhouse gases (Xie et al 2018), which also impair air quality (Mushinski et al 2019). In regions with high rates of N deposition, such as Eastern Asia (for details on regions described in this paper, see the Methods section; Vet et al 2014), an additional pulse of N from urban areas may exacerbate ecosystem damage.…”

“…), which also impair air quality (Mushinski et al . ). In regions with high rates of N deposition, such as Eastern Asia (for details on regions described in this paper, see the Methods section; Vet et al .…”

Soil microbial communities associated with giant sequoia: How does the world’s largest tree affect some of the world’s smallest organisms?

“…AMF communities were considerably more diverse beneath giant sequoia, 459 and EMF taxa such as an unidentified Byssocorticium species and Russula acrifolia were 460 more frequent and relatively abundant beneath sugar pine. While this is to be expected, 461 our findings show that differences in mycorrhizal communities in mixed stands of AMF 462 and EMF trees can be seen at the bulk soil scale, differences that can have cascading 463 effects on global scale biogeochemical processes including the cycling of carbon (Averill 464 et al, 2018) and nitrogen (Mushinski et al, 2019). 465…”

Comparisons of the effects of different drying methods on soil nitrogen fractions: Insights into emissions of reactive nitrogen gases (HONO and NO)

“…Owing to the variation in global soil moisture, it is necessary to gather soil HONO and NO flux data from 0% to 100% of the water-holding capacity for the best estimation of global soil HONO and NO emissions (Porada et al 2019;Wu et al 2019). Therefore, airdried or oven-dried soils are often used for soil HONO and NO flux measurements and estimating global emission budgets, while fresh soil samples tend to be used for mechanistic studies (Bhattarai et al 2018;Mushinski et al 2019). In this study, the maximum soil N r gas flux and total N r gas emission of freeze-dried soil were comparable with those of fresh soil, indicating that freeze-dried samples might be best for simulating fresh samples when studying soil N r gas emissions.…”