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Review
, 368 (1621), 20130126

Processes Regulating Nitric Oxide Emissions From Soils

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Review

Processes Regulating Nitric Oxide Emissions From Soils

Kim Pilegaard. Philos Trans R Soc Lond B Biol Sci.

Abstract

Nitric oxide (NO) is a reactive gas that plays an important role in atmospheric chemistry by influencing the production and destruction of ozone and thereby the oxidizing capacity of the atmosphere. NO also contributes by its oxidation products to the formation of acid rain. The major sources of NO in the atmosphere are anthropogenic emissions (from combustion of fossil fuels) and biogenic emission from soils. NO is both produced and consumed in soils as a result of biotic and abiotic processes. The main processes involved are microbial nitrification and denitrification, and chemodenitrification. Thus, the net result is complex and dependent on several factors such as nitrogen availability, organic matter content, oxygen status, soil moisture, pH and temperature. This paper reviews recent knowledge on processes forming NO in soils and the factors controlling its emission to the atmosphere. Schemes for simulating these processes are described, and the results are discussed with the purpose of scaling up to global emission.

Keywords: emission; nitric oxide; soil.

Figures

Figure 1.
Figure 1.
Transformations of mineral nitrogen in soil. The boxes for nitrification and nitrifier denitrification overlap, as nitrifier denitrification is a pathway of nitrification, but separate into the different branches from NO2 onwards. Adapted from Wrage et al. [12].
Figure 2.
Figure 2.
Coupling of atmospheric HONO with soil nitrite. Red arrows represent the multiphase processes linking gaseous HONO and soil nitrite (acid–base reaction and phase partitioning), green arrows represent biological processes, orange arrows represent heterogeneous chemical reactions converting NO2 and HNO3 into HONO and blue arrows represent other related physico-chemical processes in the N cycle. Adapted from Su et al. [18]. (Reprinted with permission from AAAS).
Figure 3.
Figure 3.
Proposed relative contributions of nitrification (solid grey shading) and denitrification (hatched shading) to gaseous N emissions as a function of water-filled pore space (WFPS). Adapted from Davidson et al. [20].
Figure 4.
Figure 4.
The relationship between NO emission and water-filled pore space (WFPS) from different forest soils in the NOFRETETE project (based on data in Schindlbacher et al. [26]).
Figure 5.
Figure 5.
Mean daily NO fluxes in throughfall exclusion and control plot dependent on the water-filled pore space in the organic layers (6 cm depth). (Reprinted from Goldberg & Gebauer [27] with permission from Elsevier.)
Figure 6.
Figure 6.
Effects of soil moisture (10 cm depth) and temperature (5 cm depth) on monthly means of soil NO fluxes. Results from NO emission measurements in the Höglwald forest during 1994–2010 (adapted from Luo et al. [30]).
Figure 7.
Figure 7.
Overview of main factors affecting NO emission from the soil: (a) linear response of NO emission versus N input or N availability, the slope is dependent on vegetation type and type of input (e.g. fertilizer application, wet deposition); (b) temperature sensitivity with a Q10 of approximately 2; (c) maximum NO emission at intermediate soil water content, moderated by soil type; (d) highest NO emission at acid conditions (chemodenitrification) and basic conditions (nitrification).

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