scholarly journals Denitrification in soil as a function of oxygen availability at the microscale

2021 ◽  
Vol 18 (3) ◽  
pp. 1185-1201
Author(s):  
Lena Rohe ◽  
Bernd Apelt ◽  
Hans-Jörg Vogel ◽  
Reinhard Well ◽  
Gi-Mick Wu ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Water Saturation ◽  
Supply And Demand ◽  
Aggregate Size ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
N2o Production ◽  
X Ray ◽  
Explanatory Variables ◽  
O2 Supply

Abstract. The prediction of nitrous oxide (N2O) and of dinitrogen (N2) emissions formed by biotic denitrification in soil is notoriously difficult due to challenges in capturing co-occurring processes at microscopic scales. N2O production and reduction depend on the spatial extent of anoxic conditions in soil, which in turn are a function of oxygen (O2) supply through diffusion and O2 demand by respiration in the presence of an alternative electron acceptor (e.g. nitrate). This study aimed to explore controlling factors of complete denitrification in terms of N2O and (N2O + N2) fluxes in repacked soils by taking micro-environmental conditions directly into account. This was achieved by measuring microscale oxygen saturation and estimating the anaerobic soil volume fraction (ansvf) based on internal air distribution measured with X-ray computed tomography (X-ray CT). O2 supply and demand were explored systemically in a full factorial design with soil organic matter (SOM; 1.2 % and 4.5 %), aggregate size (2–4 and 4–8 mm), and water saturation (70 %, 83 %, and 95 % water-holding capacity, WHC) as factors. CO2 and N2O emissions were monitored with gas chromatography. The 15N gas flux method was used to estimate the N2O reduction to N2. N gas emissions could only be predicted well when explanatory variables for O2 demand and O2 supply were considered jointly. Combining CO2 emission and ansvf as proxies for O2 demand and supply resulted in 83 % explained variability in (N2O + N2) emissions and together with the denitrification product ratio [N2O / (N2O + N2)] (pr) 81 % in N2O emissions. O2 concentration measured by microsensors was a poor predictor due to the variability in O2 over small distances combined with the small measurement volume of the microsensors. The substitution of predictors by independent, readily available proxies for O2 demand (SOM) and O2 supply (diffusivity) reduced the predictive power considerably (60 % and 66 % for N2O and (N2O+N2) fluxes, respectively). The new approach of using X-ray CT imaging analysis to directly quantify soil structure in terms of ansvf in combination with N2O and (N2O + N2) flux measurements opens up new perspectives to estimate complete denitrification in soil. This will also contribute to improving N2O flux models and can help to develop mitigation strategies for N2O fluxes and improve N use efficiency.

scholarly journals Denitrification in soil as a function of oxygen supply and demand at the microscale

2020 ◽  
Author(s):  
Lena Rohe ◽  
Bernd Apelt ◽  
Hans-Jörg Vogel ◽  
Reinhard Well ◽  
Gi-Mick Wu ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Water Saturation ◽  
Supply And Demand ◽  
Oxygen Demand ◽  
Aggregate Size ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
N2o Production ◽  
X Ray ◽  
O2 Supply

Abstract. The prediction of nitrous oxide (N2O) and of dinitrogen (N2) emissions formed by biotic denitrification in soil is notoriously difficult, due to challenges in capturing co-occurring processes at microscopic scales. N2O production and reduction depend on the spatial extent of anoxic conditions in soil, which in turn are a function of oxygen (O2) supply through diffusion and O2 demand by respiration in the presence of an alternative electron acceptor (e.g. nitrate). This study aimed to explore controlling factors of complete denitrification in terms of N2O and (N2O+N2) fluxes in repacked soils by taking micro-environmental conditions directly into account. This was achieved by measuring micro-scale oxygen saturation and estimating the anaerobic soil volume fraction (ansvf) based on internal air distribution measured with X-ray computed tomography (X-ray CT). O2 supply and demand was explored systemically in a full factorial design with soil organic matter (SOM, 1.2 and 4.5 %), aggregate size (2–4 and 4–8 mm) and water saturation (70, 83 and 95 % WHC) as factors. CO2 and N2O emissions were monitored with gas chromatography. The 15N gas flux method was used to estimate the N2O reduction to N2. N-gas emissions could only be predicted well, when explanatory variables for O2 supply and oxygen demand were considered jointly. Combining ansvf and CO2 emission as proxies of O2 supply and demand resulted in 83 % explained variability in (N2O+N2) emissions and together with the denitrification product ratio [N2O/(N2O+N2)] (pr) 72 % in N2O emissions. O2 concentration measured by microsensors was a poor predictor due to the variability in O2 over small distances combined with the small measurement volume of the microsensors. The substitution of predictors by independent, readily available proxies for O2 supply (diffusivity) and O2 demand (SOM) reduced the predictive power considerably (50 % and 58 % for N2O and (N2O+N2) fluxes, respectively). The new approach of using X-ray CT imaging analysis to directly quantify soil structure in terms of ansvf in combination with N2O and (N2O+N2) flux measurements opens up new perspectives to estimate complete denitrification in soil. This will also contribute to improving N2O flux models and can help to develop mitigation strategies for N2O fluxes and improve N use efficiency.

Oxygen supply and demand as controls of denitrification at the microscale in repacked soil

2020 ◽  
Author(s):  
Lena Rohe ◽  
Steffen Schlüter ◽  
Bernd Apelt ◽  
Hans-Jörg Vogel ◽  
Reinhard Well
Keyword(s):  
Oxygen Supply ◽  
Volume Fraction ◽  
Water Saturation ◽  
Supply And Demand ◽  
Oxygen Demand ◽  
Aggregate Size ◽  
Mitigation Strategies ◽  
X Ray ◽  
Soil Volume ◽  
Ct Image Analysis

<p>The controlling factors of biotic denitrification in soil as a source of the greenhouse gas nitrous oxide (N<sub>2</sub>O) and of dinitrogen (N<sub>2</sub>) are still not fully understood due to the challenges in observing processes that co-occur in soil at microscopic scales and the difficulty to measure N<sub>2</sub> fluxes. N<sub>2</sub>O production and reduction depend on the extent of anoxic conditions in soil, which in turn are a function of O<sub>2</sub> supply through diffusion and O<sub>2</sub> demand by soil respiration in the presence of an alternative electron acceptor (e.g. nitrate).</p><p>This study aimed to explore microscopic drivers that control total denitrification, i.e. N<sub>2</sub>O and (N<sub>2</sub>O+N<sub>2</sub>) fluxes. To provoke different levels of oxygen supply and demand, repacked soils from two locations in Germany were incubated in a full factorial design with soil organic matter (1.2 and 4.5 %), aggregate size (2-4 and 4-8mm) and water saturation (70%, 83% and 95% WHC) as factors. The sieved soils were repacked and incubated at constant temperature and moisture and gas emissions (CO<sub>2</sub> and N<sub>2</sub>O) were monitored with gas chromatography. The <sup>15</sup>N tracer application was used to estimate the N<sub>2</sub>O reduction to N<sub>2</sub>. The internal soil structure and air distribution was measured with X-ray computed tomography (X-ray CT).</p><p>The interplay of anaerobic soil volume fraction (ansvf) as an abiotic proxy of oxygen supply and CO<sub>2</sub> emission as a biotic proxy of oxygen demand resulted in 81% and 84% explained variability in N<sub>2</sub>O and (N<sub>2</sub>O+N<sub>2</sub>) emissions, respectively. These high values dropped to 5-30% when only ansvf or CO<sub>2</sub> was considered indicating strong interaction effects. The extent of N<sub>2</sub>O reduction in combination with ansvf and CO<sub>2</sub> even increased the explained variability for N<sub>2</sub>O fluxes to 83%. Average O<sub>2</sub> concentration measured by microsensors was a very poor predictor due to the extreme variability in O<sub>2</sub> at short scales in combination with the small footprint of the micro sensors probing only 0.2% of the entire soil volume. The substitution of predictors by independent, readily available proxies for O<sub>2</sub> supply (diffusivity based on air content) and O<sub>2</sub> demand (SOM) leads to a reduction in predictive power.</p><p>To our knowledge this is the first study analyzing total denitrification in combination with X-ray CT image analysis, which opens up new perspectives to estimate denitrification in soil and also contribute to improving models of N<sub>2</sub>O fluxes and fertiliser loss at all scales and can help to develop mitigation strategies for N<sub>2</sub>O fluxes and improve N use efficiency.</p>

scholarly journals A new look at an old concept: using <sup>15</sup>N<sub>2</sub>O isotopomers to understand the relationship between soil moisture and N<sub>2</sub>O production pathways

SOIL ◽  
2019 ◽  
Vol 5 (2) ◽  
pp. 265-274 ◽  
Author(s):  
Katelyn A. Congreves ◽  
Trang Phan ◽  
Richard E. Farrell
Keyword(s):  
Soil Moisture ◽  
Mitigation Strategies ◽  
Soil Conditions ◽  
Site Preference ◽  
N2o Emissions ◽  
Spectroscopic Techniques ◽  
N2o Production ◽  
Nitrification And Denitrification ◽  
The Relationship ◽  
Source Partitioning

Abstract. Understanding the production pathways of potent greenhouse gases, such as nitrous oxide (N2O), is essential for accurate flux prediction and for developing effective adaptation and mitigation strategies in response to climate change. Yet there remain surprising gaps in our understanding and precise quantification of the underlying production pathways – such as the relationship between soil moisture and N2O production pathways. A powerful, but arguably underutilized, approach for quantifying the relative contribution of nitrification and denitrification to N2O production involves determining 15N2O isotopomers and 15N site preference (SP) via spectroscopic techniques. Using one such technique, we conducted a short-term incubation where N2O production and 15N2O isotopomers were measured 24 h after soil moisture treatments of 40 % to 105 % water-filled pore space (WFPS) were established for each of three soils that differed in nutrient levels, organic matter, and texture. Relatively low N2O fluxes and high SP values indicted nitrification during dry soil conditions, whereas at higher soil moisture, peak N2O emissions coincided with a sharp decline in SP, indicating denitrification. This pattern supports the classic N2O production curves from nitrification and denitrification as inferred by earlier research; however, our isotopomer data enabled the quantification of source partitioning for either pathway. At soil moisture levels < 53 % WFPS, the fraction of N2O attributed to nitrification (FN) predominated but thereafter decreased rapidly with increasing soil moisture (x), according to FN=3.19-0.041x, until a WFPS of 78 % was reached. Simultaneously, from WFPS of 53 % to 78 %, the fraction of N2O that was attributed to denitrification (FD) was modelled as FD=-2.19+0.041x; at moisture levels of > 78 %, denitrification completely dominated. Clearly, the soil moisture level during transition is a key regulator of N2O production pathways. The presented equations may be helpful for other researchers in estimating N2O source partitioning when soil moisture falls within the transition from nitrification to denitrification.

scholarly journals Revisiting the relationship between soil moisture and N<sub>2</sub>O production pathways by measuring <sup>15</sup>N<sub>2</sub>O isotopomers

2019 ◽  
Author(s):  
Kate A. Congreves ◽  
Trang Phan ◽  
Richard E. Farrell
Keyword(s):  
Soil Moisture ◽  
Pore Space ◽  
Mitigation Strategies ◽  
Soil Conditions ◽  
Site Preference ◽  
N2o Emissions ◽  
Spectroscopic Techniques ◽  
N2o Production ◽  
Nitrification And Denitrification ◽  
The Relationship

Abstract. Understanding the production pathways of potent greenhouse gases, such as nitrous oxide (N2O), is essential for accurate flux prediction and for developing effective adaptation and mitigation strategies in response to climate change. Yet, there remain surprising gaps in our understanding and precise quantification of the underlying production pathways – such as the relationship between soil moisture and N2O production pathways. A powerful, but arguably underutilized, approach for quantifying the relative contribution of nitrification and denitrification to N2O production involves determining 15N2O isotopomers and 15N site preference (SP) via spectroscopic techniques. Using one such technique we conducted a short-term incubation to precisely quantify the relationship between soil moisture and N2O production pathways. For each of three soils, microcosms were arranged in a complete random design with four replicates; each microcosm consisted of air-dried soil packed into plastic petri dishes wherein moisture treatments were established for water contents equivalent to 45 to 105 % water-filled pore space (WFPS). The microcosms were placed in 1-L jars and sealed; headspace samples were collected after 24-h and analyzed for total N2O concentrations using gas chromatography, and for 15N2O isotopomers using cavity ring-down spectroscopy. Relatively low N2O fluxes and high SP values indicted nitrification during dry soil conditions, whereas at higher soil moisture, peak N2O emissions coincided with a sharp decline in SP indicating denitrification. This pattern supports the classic N2O production curves from nitrification and denitrification as inferred by earlier research; however, our isotopomer data enabled the quantification of source partitioning for either pathway thereby providing clarity on N2O sources during the transition from nitrification to denitrification. At soil moisture levels  78 %, denitrification completely dominated. Clearly, the soil moisture levels during transition is a key regulation of N2O production pathways.

scholarly journals Alteration of nitrous oxide emissions from floodplain soils by aggregate size, litter accumulation and plant–soil interactions

2018 ◽  
Vol 15 (22) ◽  
pp. 7043-7057 ◽  
Author(s):  
Martin Ley ◽  
Moritz F. Lehmann ◽  
Pascal A. Niklaus ◽  
Jörg Luster
Keyword(s):  
Nitrous Oxide ◽  
Leaf Litter ◽  
Hot Spots ◽  
Aggregate Size ◽  
N2o Emission ◽  
N2o Emissions ◽  
N2o Production ◽  
Plant Soil ◽  
Floodplain Soils ◽  
Plant Soil Interactions

Abstract. Semi-terrestrial soils such as floodplain soils are considered potential hot spots of nitrous oxide (N2O) emissions. Microhabitats in the soil – such as within and outside of aggregates, in the detritusphere, and/or in the rhizosphere – are considered to promote and preserve specific redox conditions. Yet our understanding of the relative effects of such microhabitats and their interactions on N2O production and consumption in soils is still incomplete. Therefore, we assessed the effect of aggregate size, buried leaf litter, and plant–soil interactions on the occurrence of enhanced N2O emissions under simulated flooding/drying conditions in a mesocosm experiment. We used two model soils with equivalent structure and texture, comprising macroaggregates (4000–250 µm) or microaggregates (<250 µm) from a N-rich floodplain soil. These model soils were planted with basket willow (Salix viminalis L.), mixed with leaf litter or left unamended. After 48 h of flooding, a period of enhanced N2O emissions occurred in all treatments. The unamended model soils with macroaggregates emitted significantly more N2O during this period than those with microaggregates. Litter addition modulated the temporal pattern of the N2O emission, leading to short-term peaks of high N2O fluxes at the beginning of the period of enhanced N2O emission. The presence of S. viminalis strongly suppressed the N2O emission from the macroaggregate model soil, masking any aggregate-size effect. Integration of the flux data with data on soil bulk density, moisture, redox potential and soil solution composition suggest that macroaggregates provided more favourable conditions for spatially coupled nitrification–denitrification, which are particularly conducive to net N2O production. The local increase in organic carbon in the detritusphere appears to first stimulate N2O emissions; but ultimately, respiration of the surplus organic matter shifts the system towards redox conditions where N2O reduction to N2 dominates. Similarly, the low emission rates in the planted soils can be best explained by root exudation of low-molecular-weight organic substances supporting complete denitrification in the anoxic zones, but also by the inhibition of denitrification in the zone, where rhizosphere aeration takes place. Together, our experiments highlight the importance of microhabitat formation in regulating oxygen (O2) content and the completeness of denitrification in soils during drying after saturation. Moreover, they will help to better predict the conditions under which hot spots, and “hot moments”, of enhanced N2O emissions are most likely to occur in hydrologically dynamic soil systems like floodplain soils.

Opportunities to reduce nitrous oxide emissions from horticultural production systems in Canada

2021 ◽  
Author(s):  
Inderjot Chahal ◽  
Khagendra R. Baral ◽  
Kate A. Congreves ◽  
Laura L. Van Eerd ◽  
C. Wagner-Riddle
Keyword(s):  
Cover Crops ◽  
Production Systems ◽  
Current Knowledge ◽  
N Fertilizer ◽  
Mitigation Strategies ◽  
Nitrous Oxide Emissions ◽  
N2o Emissions ◽  
N Losses ◽  
N2o Production ◽  
Fertilizer Application Rate

Horticultural systems, specifically vegetable production systems, are considered intensive agricultural systems as they are characterized by high nitrogen (N) fertilizer application rate, frequent tillage and irrigation operations. Accordingly, horticultural production in temperate climates is prone to N losses—mainly during post-harvest (during fall and winter) or pre-plant (spring) periods—such as N2O emissions and nitrate leaching. The risk for N losses is linked to low crop N use efficiency (NUE) combined with a narrow C:N and high N content of crop residues. Here we reviewed the studies conducted in Canada and similar climates to better understand the risk of N2O emission and potential agronomic management strategies to reduce N2O emissions from horticultural systems. Current knowledge on N2O emissions from horticultural systems indicate that increasing crop NUE, modifying the amount, type, time, and rate of N fertilizer inputs, and adopting cover crops in crop rotations are some of the effective approaches to decrease N2O emissions. However, there is uncertainty related to the efficiency of the existing N2O mitigation strategies due to the complex interactions between the factors (soil characteristics, type of plant species, climatic conditions, and soil microbial activity) responsible for N2O production from soil. Little research on N2O emissions from Canadian horticultural systems limits our ability to understand and manage the soil N2O production processes to mitigate the risk of N2O emissions. Thus, continuing to expand this line of research will help to advance the sustainability of Canadian horticultural cropping systems.

Towards a benchmarking tool for minimizing wastewater utility greenhouse gas footprints

2012 ◽  
Vol 66 (11) ◽  
pp. 2483-2495 ◽  
Author(s):  
L. Guo ◽  
J. Porro ◽  
K. R. Sharma ◽  
Y. Amerlinck ◽  
L. Benedetti ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Greenhouse Gas ◽  
Ghg Emissions ◽  
Treatment Plant ◽  
N2o Emission ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
N2o Production ◽  
Average Value ◽  
And Control

A benchmark simulation model, which includes a wastewater treatment plant (WWTP)-wide model and a rising main sewer model, is proposed for testing mitigation strategies to reduce the system's greenhouse gas (GHG) emissions. The sewer model was run to predict methane emissions, and its output was used as the WWTP model input. An activated sludge model for GHG (ASMG) was used to describe nitrous oxide (N2O) generation and release in activated sludge process. N2O production through both heterotrophic and autotrophic pathways was included. Other GHG emissions were estimated using empirical relationships. Different scenarios were evaluated comparing GHG emissions, effluent quality and energy consumption. Aeration control played a clear role in N2O emissions, through concentrations and distributions of dissolved oxygen (DO) along the length of the bioreactor. The average value of N2O emission under dynamic influent cannot be simulated by a steady-state model subjected to a similar influent quality, stressing the importance of dynamic simulation and control. As the GHG models have yet to be validated, these results carry a degree of uncertainty; however, they fulfilled the objective of this study, i.e. to demonstrate the potential of a dynamic system-wide modelling and benchmarking approach for balancing water quality, operational costs and GHG emissions.

scholarly journals Nitrite build-up effect on nitrous oxide emissions in a laboratory-scale anaerobic/aerobic/anoxic/aerobic sequencing batch reactor

2021 ◽  
Vol 16 (2) ◽  
pp. 1
Author(s):  
Larissa Coelho Auto Gomes ◽  
Barbara Costa Pereira ◽  
Renato Pereira Ribeiro ◽  
Jaime Lopes da Mota Oliveira
Keyword(s):  
Nitrous Oxide ◽  
Nitrogen Removal ◽  
Sequencing Batch Reactor ◽  
Batch Reactor ◽  
Mitigation Strategies ◽  
Nitrous Oxide Emissions ◽  
Biological Nitrogen Removal ◽  
N2o Emissions ◽  
N2o Production ◽  
Biological Nitrogen

Biological wastewater treatment processes with biological nitrogen removal are potential sources of nitrous oxide (N2O) emissions. It is important to expand knowledge on the controlling factors associated with N2O production, in order to propose emission mitigation strategies. This study therefore sought to identify the parameters that favor nitrite (NO2-) accumulation and its influence on N2O production and emission in an anaerobic/aerobic/anoxic/aerobic sequencing batch reactor with biological nitrogen removal. Even with controlled dissolved oxygen concentrations and oxidation reduction potential, the first aerobic phase promoted only partial nitrification, resulting in NO2- build-up (ranging from 29 to 57%) and consequent N2O generation. The NO2- was not fully consumed in the subsequent anoxic phase, leading to even greater N2O production through partial denitrification. A direct relationship was observed between NO2- accumulation in these phases and N2O production. In the first aerobic phase, the N2O/NO2- ratio varied between 0.5 to 8.5%, while in the anoxic one values ranged between 8.3 and 22.7%. Higher N2O production was therefore noted during the anoxic phase compared to the first aerobic phase. As a result, the highest N2O fluxes occurred in the second aerobic phase, ranging from 706 to 2416 mg N m-2 h-1, as soon as aeration was triggered. Complete nitrification and denitrification promotion in this system was proven to be the key factor to avoid NO2- build-up and, consequently, N2O emissions.

scholarly journals Alteration of nitrous oxide emissions from floodplain soils by aggregate size, litter accumulation and plant soil interactions

2018 ◽  
Author(s):  
Martin Ley ◽  
Moritz F. Lehmann ◽  
Pascal A. Niklaus ◽  
Jörg Luster
Keyword(s):  
Nitrous Oxide ◽  
Aggregate Size ◽  
Nitrous Oxide Emissions ◽  
N2o Emissions ◽  
N2o Production ◽  
Litter Accumulation ◽  
Plant Soil ◽  
Floodplain Soils ◽  
Production And Consumption ◽  
Drying Conditions

Abstract. Abstract. Semi–terrestrial soils such as floodplain soils are considered potential hotspots of nitrous oxide (N2O) emissions. Microhabitats in the soil, such as within and outside of aggregates, in the detritusphere, and/or in the rhizosphere, are considered to promote and preserve specific redox conditions. Yet, our understanding of the relative effects of such microhabitats and their interactions on N2O production and consumption in soils is still incomplete. Therefore, we assessed the effect of aggregate size, buried organic matter, and rhizosphere processes on the occurrence of enhanced N2O emissions under simulated flooding/drying conditions in a mesocosm experiment. We used two model soils with equivalent structure and texture, comprising macroaggregates (4000–250 µm) or microaggregates (

Ecological and physiological implications of nitrogen oxide reduction pathways on greenhouse gas emissions in agroecosystems

2019 ◽  
Vol 95 (6) ◽  
Author(s):  
Sukhwan Yoon ◽  
Bongkeun Song ◽  
Rebecca L Phillips ◽  
Jin Chang ◽  
Min Joon Song
Keyword(s):  
Reductase Activity ◽  
Ghg Emissions ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
Oxide Reduction ◽  
N Budget ◽  
Ghg Mitigation ◽  
N Losses ◽  
N2o Production ◽  
N2o Reductase

ABSTRACT Microbial reductive pathways of nitrogen (N) oxides are highly relevant to net emissions of greenhouse gases (GHG) from agroecosystems. Several biotic and abiotic N-oxide reductive pathways influence the N budget and net GHG production in soil. This review summarizes the recent findings of N-oxide reduction pathways and their implications to GHG emissions in agroecosystems and proposes several mitigation strategies. Denitrification is the primary N-oxide reductive pathway that results in direct N2O emissions and fixed N losses, which add to the net carbon footprint. We highlight how dissimilatory nitrate reduction to ammonium (DNRA), an alternative N-oxide reduction pathway, may be used to reduce N2O production and N losses via denitrification. Implications of nosZ abundance and diversity and expressed N2O reductase activity to soil N2O emissions are reviewed with focus on the role of the N2O-reducers as an important N2O sink. Non-prokaryotic N2O sources, e.g. fungal denitrification, codenitrification and chemodenitrification, are also summarized to emphasize their potential significance as modulators of soil N2O emissions. Through the extensive review of these recent scientific advancements, this study posits opportunities for GHG mitigation through manipulation of microbial N-oxide reductive pathways in soil.

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