Microbial nitrogen fixation and methane oxidation are strongly enhanced by light in Sphagnum mosses

Martine A R Kox,Maartje A H J Van Kessel,Eva Van Den Elzen,Mike S M Jetten,Leon P M Lamers

doi:10.1186/s13568-020-00994-9

Martine A R Kox, Maartje A H J Van Kessel + Show 3 more

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https://doi.org/10.1186/s13568-020-00994-9

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Journal: AMB Express	Publication Date: Mar 31, 2020
Citations: 17	License type: open-access

Affiliation: Radboud University Nijmegen

Abstract

Peatlands have acted as C-sinks for millennia, storing large amounts of carbon, of which a significant amount is yearly released as methane (CH4). Sphagnum mosses are a key genus in many peat ecosystems and these mosses live in close association with methane-oxidizing and nitrogen-fixing microorganisms. To disentangle mechanisms which may control Sphagnum-associated methane-oxidation and nitrogen-fixation, we applied four treatments to Sphagnum mosses from a pristine peatland in Finland: nitrogen fertilization, phosphorus fertilization, CH4 addition and light. N and P fertilization resulted in nutrient accumulation in the moss tissue, but did not increase Sphagnum growth. While net CO2 fixation rates remained unaffected in the N and P treatment, net CH4 emissions decreased because of enhanced CH4 oxidation. CH4 addition did not affect Sphagnum performance in the present set-up. Light, however, clearly stimulated the activity of associated nitrogen-fixing and methane-oxidizing microorganisms, increasing N2 fixation rates threefold and CH4 oxidation rates fivefold. This underlines the strong connection between Sphagnum and associated N2 fixation and CH4 oxidation. It furthermore indicates that phototrophy is a strong control of microbial activity, which can be directly or indirectly.

Highlights

The large amounts of carbon (C) stored in Northern peatlands are severely threatened by anthropogenic disturbances of these vulnerable ecosystems due to for example drainage, fires and N-fertilization (Turetsky et al 2002; Bragazza et al 2012; Andersen et al 2013; Abdalla et al 2016; Leifeld and Menichetti 2018)
In addition to the limited pool of environmentally available N, N required for growth is provided by microbial N2 fixation via Sphagnum-associated microorganisms, which may account for the mismatch between the high N-content of Sphagnum mosses and the low input of N via atmospheric deposition (Vile et al 2014)
Here we investigate the environmental drivers of microbial N2 fixation and C H4 oxidation in pristine Sphagnum mosses

Summary

Introduction

The large amounts of carbon (C) stored in Northern peatlands (representing 250–450 Pg C; Frolking and Roulet 2007) are severely threatened by anthropogenic disturbances of these vulnerable ecosystems due to for example drainage, fires and N-fertilization (Turetsky et al 2002; Bragazza et al 2012; Andersen et al 2013; Abdalla et al 2016; Leifeld and Menichetti 2018). Over millennia peatlands have acted as net C-sinks, sequestering and storing more C than is emitted to the atmosphere, thereby counteracting global warming (Gorham 1991; Rydin and Jeglum 2006; Frolking and Roulet 2007; Loisel et al 2014; Leifeld and Menichetti 2018). Most Sphagnum species thrive in nitrogen (N) limited environments (Aerts et al 1992) and do so by monopolizing the majority of atmospheric N deposited (Fritz et al 2014). In addition to the limited pool of environmentally available N, N required for growth is provided by microbial N2 fixation via Sphagnum-associated microorganisms, which may account for the mismatch between the high N-content of Sphagnum mosses and the low input of N via atmospheric deposition (Vile et al 2014). In younger peatlands, N2 fixation by methane-oxidizing microorganisms is assumed to be responsible for N accumulation in Sphagnum (Larmola et al 2014), providing a strong link between the CH4-cycle and N-cycle in Sphagnum-dominated peatlands (Ho and Bodelier 2015)

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