Soil HONO emissions at high moisture content are driven by microbial nitrate reduction to nitrite: tackling the HONO puzzle

Carbonyl sulfide (OCS) exchange between soils and the atmosphere affected by soil moisture and compensation points

<p><strong>Abstract.</strong> Carbonyl sulfide (OCS) is a chemically quite stable gas in the troposphere (lifetime ~<span class="thinspace"></span>2&amp;ndash;6 years) and consequently some of it is transported up to the stratosphere where it contributes to the stratospheric sulfate layer. Due to the similarities in uptake mechanism between OCS and CO₂, the use of OCS as a proxy for CO₂ in ecosystem gross primary production (GPP) has been proposed. For this application a good understanding of uptake (U_OCS) and production (P_OCS) processes of OCS in an ecosystem is required. A new OCS quantum cascade laser coupled with an automated soil chamber system enabled us to measure the soil-atmosphere OCS exchange of four different soil samples with high precision. The adjustment of the chamber air to different OCS mixing ratios (50, 500, and 1000<span class="thinspace"></span>ppt) allowed us to separate production and consumption processes and to estimate compensation points (CPs) for the OCS exchange. At an atmospheric mixing ratio of 1000<span class="thinspace"></span>ppt, the maximum U_OCS was of the order of 22 to 110<span class="thinspace"></span>pmol<span class="thinspace"></span>g^&amp;minus;1<span class="thinspace"></span>h^&amp;minus;1 for needle forest soil samples and of the order of 3 to 5<span class="thinspace"></span>pmol<span class="thinspace"></span>g^&amp;minus;1<span class="thinspace"></span>h^&amp;minus;1 for an agricultural mineral soil, both measured at moderate soil moisture. Uptake processes (U_OCS) were dominant at all soil moistures for the forest soils, while P_OCS exceeded U_OCS at higher soil moistures for the agricultural soil, resulting in net emission. Hence, our results indicate that in (spruce) forests U_OCS might be the dominant process, while in agricultural soils P_OCS at higher soil moisture and U_OCS under moderate soil moisture seem to dominate the OCS exchange. The OCS compensation points (CPs) were highly dependent on soil water content and extended over a wide range of 130<span class="thinspace"></span>ppt to 1600<span class="thinspace"></span>ppt for the forest soils and 450<span class="thinspace"></span>ppt to 5500<span class="thinspace"></span>ppt for the agricultural soil. The strong dependency between soil water content and the compensation point value must be taken into account for all further analyses. The lowest CPs were found at about 20<span class="thinspace"></span>% water filled pore space (WFPS_lab), implying the maximum of U_OCS under these soil moisture conditions and excluding OCS emission under such conditions. We discuss our results in view of other studies about compensation points and the potential contribution of microbial groups.</p>

Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote atmosphere in Cyprus

<p><strong>Abstract.</strong> Soil and biological soil crusts can emit nitrous acid (HONO) and nitric oxide (NO). The terrestrial ground surface in arid and semiarid regions is anticipated to play an important role in the local atmospheric HONO budget, deemed to represent one of the unaccounted-for HONO sources frequently observed in field studies. In this study HONO and NO emissions from a representative variety of soil and biological soil crust samples from the Mediterranean island Cyprus were investigated under controlled laboratory conditions. A wide range of fluxes was observed, ranging from 0.6 to 264 ng m<span class="inline-formula">⁻²</span> s<span class="inline-formula">⁻¹</span> HONO-N at optimal soil water content (20–30 % of water holding capacity, WHC). Maximum NO-N fluxes at this WHC were lower (0.8–121 ng m<span class="inline-formula">⁻²</span> s<span class="inline-formula">⁻¹)</span>. The highest emissions of both reactive nitrogen species were found from bare soil, followed by light and dark cyanobacteria-dominated biological soil crusts (biocrusts), correlating well with the sample nutrient levels (nitrite and nitrate). Extrapolations of lab-based HONO emission studies agree well with the unaccounted-for HONO source derived previously for the extensive CYPHEX field campaign, i.e., emissions from soil and biocrusts may essentially close the Cyprus HONO budget.</p>

Photoautotrophic organisms control microbial abundance, diversity, and physiology in different types of biological soil crusts

Emission of nitrous acid from soil and biological soil crusts represents a dominant source of HONO in the remote atmosphere in Cyprus

Soil and biological soil crusts can emit nitrous acid (HONO) and nitric oxide (NO). The terrestrial ground surface in arid and semi-arid regions is anticipated to play an important role in the local atmospheric HONO budget, deemed to represent one of the unaccounted HONO sources frequently observed in field studies. In this study HONO and NO emissions from a representative variety of soil and biological soil crust samples from the Mediterranean island Cyprus were investigated under controlled laboratory conditions. A wide range of fluxes was observed, ranging from 0.6 to 264&amp;thinsp;ng&amp;thinsp;m^&amp;minus;2&amp;thinsp;s^&amp;minus;1 HONO-N at optimal soil water content (20&amp;ndash;30&amp;thinsp;% of water holding capacity, WHC). Maximum NO-N at this WHC fluxes were lower (0.8&amp;ndash;121&amp;thinsp;ng&amp;thinsp;m^&amp;minus;2&amp;thinsp;s^&amp;minus;1). Highest emissions of both reactive nitrogen species were found from bare soil, followed by light and dark cyanobacteria-dominated biological soil crusts (biocrusts), correlating well with the sample nutrient levels (nitrite and nitrate). Extrapolations of lab-based HONO emission studies agree well with the unaccounted HONO source derived previously for the extensive CYPHEX field campaign, i.e., emissions from soil and biocrusts may essentially close the Cyprus HONO budget.

Soil dissimilatory nitrate reduction processes in the Spartina alterniflora invasion chronosequences of a coastal wetland of southeastern China: Dynamics and environmental implications

Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands

N2O consumption by low-nitrogen soil and its regulation by water and oxygen