Genomic evidence that microbial carbon degradation is dominated by iron redox metabolism in thawing permafrost.

Microorganisms drive many aspects of organic carbon cycling in thawing permafrost soils, but the compositional trajectory of the post-thaw microbiome and its metabolic activity remain uncertain, which limits our ability to predict permafrost-climate feedbacks in a warming world. Using quantitative metabarcoding and metagenomic sequencing, we determined relative and absolute changes in microbiome composition and functional gene abundance during thaw incubations of wet sedge tundra collected from northern Alaska, USA. Organic soils from the tundra active-layer (0-50 cm), transition-zone (50-70 cm), and permafrost (70+ cm) depths were incubated under reducing conditions at 4 °C for 30 days to mimic an extended thaw duration.

Ecosystem feedbacks constrain the effect of day-to-day weather variability on land-atmosphere carbon exchange.

Whole-ecosystem interactions and feedbacks constrain ecosystem responses to environmental change. The effects of these constraints on responses to climate trends and extreme weather events have been well studied. Here we examine how these constraints respond to changes in day-to-day weather variability without changing the long-term mean weather.

Summer thaw duration is a strong predictor of the soil microbiome and its response to permafrost thaw in arctic tundra.

Climate warming has increased permafrost thaw in arctic tundra and extended the duration of annual thaw (number of thaw days in summer) along soil profiles. Predicting the microbial response to permafrost thaw depends largely on knowing how increased thaw duration affects the composition of the soil microbiome. Here, we determined soil microbiome composition from the annually thawed surface active layer down through permafrost from two tundra types at each of three sites on the North Slope of Alaska, USA.

Heterotrophic Bacteria Dominate Catalase Expression during Blooms.

In the oligotrophic oceans, key autotrophs depend on "helper" bacteria to reduce oxidative stress from hydrogen peroxide (HO) in the extracellular environment. HO is also a ubiquitous stressor in freshwaters, but the effects of HO on autotrophs and their interactions with bacteria are less well understood in freshwaters. Naturally occurring HO in freshwater systems is proposed to impact the proportion of microcystin-producing (toxic) and non-microcystin-producing (nontoxic) in blooms, which influences toxin concentrations and human health impacts.

Interannual, summer, and diel variability of CH and CO effluxes from Toolik Lake, Alaska, during the ice-free periods 2010-2015.

Accelerated warming in the Arctic has led to concern regarding the amount of carbon emission potential from Arctic water bodies. Yet, aquatic carbon dioxide (CO) and methane (CH) flux measurements remain scarce, particularly at high resolution and over long periods of time. Effluxes of methane (CH) and carbon dioxide (CO) from Toolik Lake, a deep glacial lake in northern Alaska, were measured for the first time with the direct eddy covariance (EC) flux technique during six ice-free lake periods (2010-2015).