The role of abiotic processes in the formation and degradation of gaseous nitrogen compounds in the soil
Buch in deiner Nähe kaufen
Beschreibung
Soils are a major source of nitrogen (N) trace gases, especially of nitrous oxide (N2O) and nitric
oxide (NO). The two microbial processes nitrification and denitrification are considered the major
contributors to these emissions. While microbial denitrification has long been identified as a source
of N trace gases under reducing conditions, N trace gas formation under aerobic conditions is far
from being completely understood. Several abiotic reactions involving the nitrification intermediates
hydroxylamine (NH2OH) and nitrite (NO2
–) have been identified leading to N2O and NO emissions,
but are neglected in most current studies. Further, there is a potential abiotic sink function of
soils for N2O via photochemical destruction. For better N trace gas mitigation strategies, the identification
of the major source and sink processes and their role in the global N cycle is vital.
Prior to the experimental work, this thesis reviews information about the role of abiotic processes
in the formation of N trace gases from the few available studies reporting on abiotic emissions. It
merges the gained information into a new conceptual model explaining the formation of the N trace
gases N2O, NO, as well as gaseous nitrous acid (HONO) by coupled biotic–abiotic reaction mechanisms.
The relevant reactions are: the self-decomposition of NO2
–, reactions of NO2
– with reduced
metal cations, the nitrosation of soil organic matter (SOM) by NO2
–, the comproportionation of
NO2
– and NH2OH, and the oxidation of NH2OH by manganese or iron. While reactions involving
NO2
– have been shown to produce primarily NO, reactions of NH2OH are known to lead to N2O as
their main product.
In soils it is difficult to discriminate between biological and abiotic processes. Here, stable isotope
techniques are a promising tool to give more insight into the production processes. Especially the
site preference (SP) of 15N in N2O can help to source partition between processes. Experiments
have been designed to study the abiotic formation of N2O from NH2OH in solutions and in different
non-sterile and sterile soils from forest, grassland, and cropland. While organic forest soils
showed hardly any N2O formation upon NH2OH addition, an immediate and strong formation of
N2O was observed in cropland soil, also in sterilized samples. A correlation analysis revealed a
potential positive relationship of the NH2OH-induced N2O formation with soil pH and manganese
content, construing an effect of pH on NH2OH stability and of manganese acting as an oxidation
agent for NH2OH. A negative correlation between abiotic N2O formation and C/N ratio was found
that could indicate a possible competitive reaction of NH2OH with functional groups of SOM. All
abiotic N2O production pathways showed a characteristic, high SP unaffected by reaction conditions.
Autor*in
Jannis Heil
Themen in »The role of abiotic processes in the formation and degradation of gaseous nitrogen compounds in the soil«
Agricultural practices N2O Soil Properties