Effects of Nitrogen Load on the Function and Diversity of Methanotrophs in the Littoral Wetland of a Boreal Lake

Pertti J Martikainen,Levente Bodrossy,Henri M P Siljanen,Anne Saari

doi:10.3389/fmicb.2012.00039

Abstract

Methane is the second most abundant greenhouse gas in the atmosphere. A major part of the total methane emissions from lake ecosystems is emitted from littoral wetlands. Methane emissions are significantly reduced by methanotrophs, as they use methane as their sole energy and carbon source. Methanotrophic activity can be either activated or inhibited by nitrogen. However, the effects of nitrogen on methanotrophs in littoral wetlands are unknown. Here we report how nitrogen loading in situ affected the function and diversity of methanotrophs in a boreal littoral wetland. Methanotrophic community composition and functional diversity were analyzed with a particulate methane monooxygenase (pmoA) gene targeted microarray. Nitrogen load had no effects on methane oxidation potential and methane fluxes. Nitrogen load activated pmoA gene transcription of type I (Methylobacter, Methylomonas, and LW21-freshwater phylotypes) methanotrophs, but decreased the relative abundance of type II (Methylocystis, Methylosinus trichosporium, and Methylosinus phylotypes) methanotrophs. Hence, the overall activity of a methanotroph community in littoral wetlands is not affected by nitrogen leached from the catchment area.

Highlights

Methane (CH4) is the second most abundant greenhouse gas in the atmosphere after carbon dioxide
When the site had received 50% of the total nitrogen load there was a decrease in the relative abundance of particulate methane monooxygenase (pmoA) genes of type II (Methylocystis, Methylosinus trichosporium, and Methylosinus phylotypes, P < 0.05) methanotrophs in the 0to 10-cm soil layers (Figure 3A; Figure A3A in Appendix)
correspondence analysis (CCA) multivariate ordination analysis revealed a correlation between the concentrations of ammonium and nitrate and microarray data measured during nitrogen loading in affected soil layers and gene pools, as samples during the experiment are clustered together with the ordinated arrows for ammonium and nitrate (Figures 3B–D)

Summary

Introduction

Methane (CH4) is the second most abundant greenhouse gas in the atmosphere after carbon dioxide. It is 25 times more efficient (with a time horizon of 100 years) as a greenhouse gas than carbon dioxide (Denman et al, 2007). It accounts for about 20% of the radiative forcing (warming effect) of the atmosphere (Denman et al, 2007). Proteobacterial methanotrophs are divided into two classes, Gammaproteobacteria and Alphaproteobacteria (often referred to as type I and type II methanotrophs, respectively) on the basis of phylogeny, physiology, morphology, and biochemistry (Semrau et al, 2010). Type I methanotrophs are further divided into type Ia and type Ib subgroups based on their phylogeny (Bodrossy et al, 2003)

Methods

Results

Conclusion