Microbial drivers of methane emissions from unrestored industrial salt ponds

Jinglie Zhou,Ye Tian,Susannah G Tringe,Clifton P Bueno De Mesquita,Wyatt H Hartman,Susanna M Theroux

doi:10.1038/s41396-021-01067-w

Abstract

Wetlands are important carbon (C) sinks, yet many have been destroyed and converted to other uses over the past few centuries, including industrial salt making. A renewed focus on wetland ecosystem services (e.g., flood control, and habitat) has resulted in numerous restoration efforts whose effect on microbial communities is largely unexplored. We investigated the impact of restoration on microbial community composition, metabolic functional potential, and methane flux by analyzing sediment cores from two unrestored former industrial salt ponds, a restored former industrial salt pond, and a reference wetland. We observed elevated methane emissions from unrestored salt ponds compared to the restored and reference wetlands, which was positively correlated with salinity and sulfate across all samples. 16S rRNA gene amplicon and shotgun metagenomic data revealed that the restored salt pond harbored communities more phylogenetically and functionally similar to the reference wetland than to unrestored ponds. Archaeal methanogenesis genes were positively correlated with methane flux, as were genes encoding enzymes for bacterial methylphosphonate degradation, suggesting methane is generated both from bacterial methylphosphonate degradation and archaeal methanogenesis in these sites. These observations demonstrate that restoration effectively converted industrial salt pond microbial communities back to compositions more similar to reference wetlands and lowered salinities, sulfate concentrations, and methane emissions.

Highlights

Wetlands are land areas saturated or covered with water and are a transition zone between dry land and bodies of water
The relative importance of these different pathways depends on temperature, organic matter quality, the rates of intermediate processes such as acetogenesis or acetate oxidation, and the presence of alternate electron acceptors such as nitrate, sulfate, or iron, whose reduction competes with methanogenesis to consume acetate and hydrogen [8]
We explored the microbial communities in these four wetland sites through both 16S rRNA gene profiling and shotgun metagenome sequencing, in parallel with greenhouse gas measurements and sediment biogeochemical characterization, to investigate the biogeochemical and microbiological effects of restoration

Summary

Introduction

Wetlands are land areas saturated or covered with water and are a transition zone between dry land (upland) and bodies of water. The co-occurrence network of all OTUs from all three site types (Spearman’s |r| > 0.9) indicated that OTUs specific to restored salt ponds and reference wetlands shared more positive correlations compared to those shared with unrestored salt ponds (Fig. S2b).

Results

Conclusion