On the origin of nitrous oxide and its oxygen

Lachgas (N2O) is een broeikasgas dat bijdraagt aan de opwarming van de aarde en de afbraak van ozon in de stratosfeer. Om emissies van N2O terug te dringen zullen we moeten begrijpen hoe en waar het ontstaat. Er is echter veel onduidelijkheid over de verschillende manieren waarop N2O wordt gevormd, en hoe deze processen worden beïnvloed door de omgeving. Wereldwijd vormen bodems de grootste bron van lachgas naar de atmosfeer. Met mijn onderzoek probeer ik daarom een beter inzicht te krijgen in de productie van N2O in bodems. Mijn hoofddoel was om de bijdrage van ‘nitrifier denitrification’ als afzonderlijk proces te bestuderen. In dit proces wordt nitriet (NO2-) omgezet in N2O door ammonia oxiderende bacteriën (AOB), die normaliter juist NO2- vormen vanuit ammonia (NH3). Het reducerende proces tot N2O wordt normaal gesproken voornamelijk toegeschreven aan andere organismen, de denitrificeerders

Oxidation and compaction of a collapsed peat dome in Central Kalimantan

Peat domes in Kalimantan (Indonesia) are reported to loose their dome shape as a result of disturbance such as logging and artificial drainage. The loss of the dome shape can be caused by (a combination of) two major processes: compaction and oxidation. Because natural, undisturbed peat is a major sink for atmospheric CO2, the distinction between the two processes is of utmost importance with regard to carbon storage. In case of compaction, no CO2 need to be lost to the atmosphere. In case of oxidation, either as a result of increased decomposition upon improved drainage or by burning, all CO produced goes to the atmosphere. To estimate the contribution of oxidation and compaction to the loss of peat dome shape, research was conducted in the Mawas area in Central Kalimantan. Physical and chemical parameters of an intact and collapsed dome were compared. Increased bulk densities in the collapsed peat dome showed that considerable compaction has occurred. Depending on the initial bulk density, compaction has probably caused a subsidence from 2.2 to 4.0 in. According to ash content measurements, no significant oxidation has taken place, but increased EC found at the collapsed dome can be due to oxidation of at least 2.3 cur to 46.9 cm peat, which implies an emission of respectively 4.2 to 85.9 kg CO2 m(-2) over the 6 years since collapse. Compaction appeared to be a more important factor in the loss of dome structure than oxidation based on the estimated possible ranges in peat loss. Collapse of the dome had only minor influence on its chemical parameters. Regrowth did not seem to be hindered by the collapse and its consequences, but it was less at sites that had suffered recent fires. If peat growth resumes, collapse need not be detrimental to carbon storage. (c) 2006 Elsevier B.V. All rights reserved

Source Determination of Nitrous Oxide Based on Nitrogen and Oxygen Isotope Tracing: Dealing with Oxygen exchange

Source determination of nitrous oxide (N2O) from soils has so far been complicated by methodological constraints: the frequently used 15N tracer method could not differentiate between pathways related to nitrification, that is, nitrifier nitrification (NN), nitrifier denitrification (ND), and nitrification-coupled denitrification (NCD). To overcome this problem, a dual isotope method using both 15N and 18O was proposed. However, O exchange between nitrogen oxides and water has been found to disturb such a method. We here explain in detail a novel dual isotope method that allows to quantify O exchange in denitrification and to differentiate N2O production from NN, ND, NCD, and fertilizer denitrification (FD). The method has already been applied to a range of soils with good success. Potential of and scope for further improvement of the method are discusse

Source Determination of Nitrous Oxide Based on Nitrogen and Oxygen Isotope Tracing: Dealing with Oxygen exchange

Source determination of nitrous oxide (N2O) from soils has so far been complicated by methodological constraints: the frequently used 15N tracer method could not differentiate between pathways related to nitrification, that is, nitrifier nitrification (NN), nitrifier denitrification (ND), and nitrification-coupled denitrification (NCD). To overcome this problem, a dual isotope method using both 15N and 18O was proposed. However, O exchange between nitrogen oxides and water has been found to disturb such a method. We here explain in detail a novel dual isotope method that allows to quantify O exchange in denitrification and to differentiate N2O production from NN, ND, NCD, and fertilizer denitrification (FD). The method has already been applied to a range of soils with good success. Potential of and scope for further improvement of the method are discusse

Inhibition of denitrification and N2O emission by urine-derived benzoic and hippuric acid

Hippuric acid (HA) in cattle urine acts as a natural inhibitor of soil N2O emissions. As HA concentration varies with diet, we determined critical HA levels. We also tested the hypothesis that the inhibition occurs because the HA breakdown product benzoic acid (BA) inhibits denitrification rates. During a 64-day incubation, we quantified emissions from artificial urine varying in HA, BA and glycine (Gly) concentrations, added to a sandy pasture soil. Increasing HA concentration from 0.4 to 5.6 mmol kg¿1 soil significantly decreased the average N2O flux by 54%. At 3.9 mmol kg¿1 soil, denitrification levels were 50% reduced for BA as compared to Gly. We conclude that HA inhibits both denitrification and N2O emission, at least partly through a BA mechanism

Nitrifier denitrification as a distinct and significant source of nitrous oxide from soil

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Increased hippuric acid content of urine can reduce soil N2O fluxes

Urine patches in grazed pastures are a major source of nitrous oxide (N2O) emission. It is well-documented that the relative concentration of the various nitrogenous urine constituents varies significantly with diet. The effect of these variations on NO emissions from urine patches, however, has never been reported. The aim of this study was to test whether variations in urine composition, consistent with different diets, lead to significant differences in N2O emission. Four varieties of artificial urine, all with similar total N concentrations, but varying in the relative contribution of the nitrogenous constituents, were applied to undisturbed cores from a sandy pasture soil. N2O fluxes were monitored for 65 days at two moisture treatments; 92% WFPS for the entire incubation, and 70% WFPS up to day 41 and 92% afterwards. Extra replicates were included for destructive analysis on mineral N concentrations and pH. Urine composition was a significant (P <0.001) factor determining N2O emissions. An increase in the relative hippuric acid concentration from 3 to 9% of total N resulted in a significant decline in average N2O fluxes, from 16.4 to 8.7 mu g N2O-N h(-1) kg(-1) soil (averaged over all treatments). Cumulative emission decreased from 8.4 to 4.4% of the applied urine-N (P <0.0 1). Soil mineral N showed a modest but significant decrease with an increase of hippuric acid content. pH did not show any significant relationship with urine composition. Increasing the urea concentration with 12% of applied urinary N did not significantly affect N2O emissions. Moisture content significantly affected N2O emissions (P <0.001), but no interaction between moisture and urine composition was found. As the inhibitory effect of hippuric acid could not be linked directly to mineral N concentrations in the soil, we hypothesize that the breakdown product benzoic acid either inhibits denitrification or decreases the N2O/N-2 ratio. We conclude that hippuric acid concentration in urine is an important factor influencing N2O emission, with a potential for reducing emissions with 50%. We suggest alternative rationing leading to higher hippuric acid concentrations in urine as a possible strategy to mitigate N2O emission from grazed pastures. (c) 2005 Elsevier Ltd. All fights reserved

What artificial urine composition is adequate for simulating soil N2O fluxes and mineral N dynamics?

Artificial urine, an aqueous solution of various nitrogenous compounds and salts, is routinely used in soil incubation studies on nitrous oxide (N2O) emissions and related nitrogen (N) and pH dynamics. There is, however, no consensus on artificial urine composition, and a wide variety of compositions are used. The aim of this study was to test which artificial urine composition is adequate for simulating N2O fluxes, respiration, soil mineral N and pH dynamics of real cattle urine in both short- and long-term incubation studies. Urine solutions of differing compositions were applied to a sandy soil and incubated for 65 days, and results of measurements on N2O fluxes and soil mineral N were analyzed over the first 5 days as well as over the whole incubation period. Results from two real cattle urines with known nitrogenous composition (R1 and R2) were compared with three artificial urine types: (i) urea+glycine (AG), (ii) urea+hippuric acid (AH) and (iii) an artificial urine identical to the nitrogenous composition of real urine R1 (AR). During the first 5 days, only cumulative N2O emissions for AG deviated significantly (P=0.02) from the N2O emissions for real urines, with 0.4% of applied N emitted compared with 0.0% and 0.1% for R1 and R2, respectively. Respiration from R1 was significantly (

Autotrophic carbon dioxide fixation via the calvin-benson-bassham cycle by the denitrifying methanotroph "candidatus methylomirabilis oxyfera"

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