# Activity and Abundance of Nitrous Oxide Reducing Bacteria in Platismatia glauca : An Epiphytic Lichen in the Boreal Spruce Forest

## TL;DR

This study shows that the lichen Platismatia glauca consumes nitrous oxide in boreal forests, thanks to bacteria with the nosZ gene.

## Contribution

The study identifies P. glauca as a net consumer of N2O, emphasizing its role in nitrogen cycling through lichen-microbiome interactions.

## Key findings

- P. glauca consumes N2O at rates of 0.1–0.4 ng N2O–N g DW−1 h−1 under aerobic conditions.
- The nosZ gene, associated with N2O reduction, is active and abundant in P. glauca, especially at +5°C.
- Clade I nosZ sequences are primarily affiliated with Rhizobiales bacteria in the lichen.

## Abstract

The nitrous oxide (N2O) dynamics in boreal forests are better known at the ecosystem scale, with greater uncertainty associated with specific ecosystem compartments. We investigated the N2O dynamics of the lichen
Platismatia glauca
in boreal forests near Kuopio, North Savo, Finland. At the study sites,
P. glauca
is the most abundant lichen colonising Norway spruce (Picea abies). Despite their abundance, the contribution of epiphytic lichens like
P. glauca
to N2O dynamics in boreal forests has received little attention. By incubating
P. glauca
, we assessed the effects of moisture, temperature, and oxygen availability on its N2O dynamics. We observed net N2O consumption potential, particularly at +5°C at aerobic condition. Quantitative real‐time PCR analysis targeting the N2O reductase gene fragment (nosZ) revealed that it was present and active in both in situ and incubated lichens. nosZ transcription was higher at +5°C. Clade I nosZ was dominant, with most sequences affiliated with the order Rhizobiales. We confirmed the presence of nosZ gene with targeted metagenomics sequencing. Our results demonstrate that
P. glauca
acts as a net consumer of N2O, with potential ranging between 0.1 and 0.4 ng N2O–N g DW−1 h−1 under aerobic conditions.

The boreal epiphytic lichen
Platismatia glauca
acts as an overlooked sink for atmospheric N2O through its association with nosZ Clade I bacteria, highlighting the contribution of lichen–microbiome interactions to nitrogen cycling and N2O exchange in forest ecosystems.