RNA Stable Isotope Probing of Potential Feammox Population in Paddy Soil

Anaerobic
ammonium oxidation coupled to iron reduction (Feammox)
is a recently discovered pathway contributing to nitrogen loss in
various ecosystems such as paddy soils and sediments. However, little
is known about the microbes driving Feammox in an agricultural ecosystem.
Here, we demonstrated the occurrence of Feammox in paddy soils of
Southern China using a 15N isotopic tracing technique,
and examined the microbial communities associated with Feammox using
RNA based stable isotope probing (RNA-SIP) combined with Illumina
sequencing. Feammox was detected in all collected soils with direct
N2 production as the dominant Feammox pathway. It was estimated
that approximately 6.91% of the applied nitrogen fertilizers were
lost through Feammox in the paddy soils. RNA-SIP results showed that
the composition of enriched active microbial communities were dependent
on soil properties, especially the soil pH and grain size. Geobacter were enriched in most soils across various properties.
The abundance of enriched GOUTA19 were significantly higher in soils
with low pH than those in soils with medium pH and high pH, and the
relative abundance of active Nitrososphaeraceae and Pseudomonas only increased in soils with medium and high pH during 4-day of
incubation. These results suggested Feammox is a ubiquitous and important
process for N loss. Geobacter, GOUTA19, Nitrososphaeraceae and Pseudomonas were active during the incubation that favored
Feammox and the growth of Feammox microbes, suggesting these microbes
were potentially associated with Feammox in natural agricultural soils.