Soil biochar amendment affects the diversity of nosZ transcripts: Implications for N2O formation

Johannes Harter,Andreas Kappler,Mohamed El-Hadidi,Daniel H Huson,Sebastian Behrens

doi:10.1038/s41598-017-03282-y

Abstract

Microbial nitrogen transformation processes such as denitrification represent major sources of the potent greenhouse gas nitrous oxide (N2O). Soil biochar amendment has been shown to significantly decrease N2O emissions in various soils. However, the effect of biochar on the structure and function of microbial communities that actively perform nitrogen redox transformations has not been studied in detail yet. To analyse the community composition of actively denitrifying and N2O-reducing microbial communities, we collected RNA samples at different time points from a soil microcosm experiment conducted under denitrifying conditions and performed Illumina amplicon sequencing targeting nirK, typical nosZ and atypical nosZ mRNA transcripts. Within 10 days, biochar significantly increased the diversity of nirK and typical nosZ transcripts and resulted in taxonomic shifts among the typical nosZ-expressing microbial community. Furthermore, biochar addition led to a significant increase in transcript production among microbial species that are specialized on direct N2O reduction from the environment. Our results point towards a potential coupling of biochar-induced N2O emission reduction and an increase in microbial N2O reduction activity among specific groups of typical and atypical N2O reducers. However, experiments with other soils and biochars will be required to verify the transferability of these findings to other soil-biochar systems.

Highlights

Microbial nitrogen transformation processes such as denitrification represent major sources of the potent greenhouse gas nitrous oxide (N2O)
Transcript sequencing resulted in 3,404,618 raw pairs of reads in total with nirK, typical nosZ, and atypical nosZ accounting for 733,518 (40,751 ± 13,287 per sample), 2,064,131 (114,674 ± 35,377 per sample), and 606,969 (33,721 ± 9,523 per sample) raw read pairs, respectively
Highest N2O emission rates usually occur after heavy rain fall when high amounts of organic carbon and mineral nitrogen are mobilized and oxygen availability decreases due to high water filled pore spaces (WFPS)[17, 18]

Summary

Introduction

Microbial nitrogen transformation processes such as denitrification represent major sources of the potent greenhouse gas nitrous oxide (N2O). The majority of these microorganisms carry a fully functional but atypical form of the nosZ gene and about half of them do not contain a nitrite reductase gene[27,28,29] It has been confirmed in many studies that soil biochar amendment holds the potential to act as promising N2O mitigation strategy the underlying processes causing a decrease in N2O emissions are still not fully understood. Because N2O is formed during microbial nitrogen transformation reactions such as nitrification and especially denitrification, several studies aimed to link N2O emission suppression to changes in the structure and activity of microbial communities involved in nitrogen cycling[30,31,32,33,34,35] It is known from 16S rRNA gene-based molecular fingerprinting and sequencing studies that the addition of biochar can significantly affect the microbial diversity in soil. The impact of soil biochar amendment on the diversity and taxonomic composition of active denitrifiers and N2O reducing microbial taxa has not yet been systematically investigated on the transcript level

Methods

Results

Conclusion