Complex microbiome and methane flux changes in response to metals in transitional grassland soil

Background/Question/Methods

Methane is a significant contributor to global warming; by some estimates, it is responsible for 20–30% of observed atmospheric warming. Although much of the recent contribution to global methane levels is anthropogenic, microbes play a major role as producers and consumers of atmospheric methane. Previous studies have shown that global biogeochemical cycles are strongly impacted by microbial responses to nutrients and heavy metals in the environment.

Prior studies in marine systems and chronically flooded soils have shown that nickel causes an increase in the net release of methane, while copper reduces net methane release, or induces greater methane uptake. However, similar work has not been done in non-wetland, terrestrial soils, such as those found in scrublands. The goals of this study were to: (1) quantify methane flux and (2) examine soil microbial community composition and activity in response to copper and nickel. To achieve these goals, we collected scrubland soil, and manipulated aliquots of soil under various combinations of water and heavy metals. The resultant daily flux was measured using a gas chromatograph over 14 days post-wet-up. Microbial community composition and activity will be determined using high-throughput DNA sequencing and qRT-PCR to elucidate the mechanisms of changes in methane flux.

Results/Conclusions

The data reveal that methane, carbon dioxide, and nitrous oxide fluxes in these soils are strongly affected by the addition of water and copper. The relationship of these greenhouses gas fluxes to the quantity of water is non-linear: increased gas release with moderate amounts of water, but decreased release at high levels of water saturation. This suggests multilayered, opposing effects of soil saturation on microbial communities. The addition of copper to the soils results in significantly reduced trace greenhouse gas levels within the first days post wet-up, reversing the increased release observed with moderate amounts of water alone. These data could be used in comprehensive global climate and biogeochemical models, demonstrating the complex contribution of dry soils to greenhouse gas flux, particularly as global warming and anthropogenic environmental changes affect rainfall, and pollution impacts the heavy metal levels in these areas.