Rewetting the wasteland

Do microbes find their way back?

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Humans have been draining peatlands for centuries. With time we have come to realize that such drained “wastelands" do more than just supply nutrition for our crops; they are also emitting gigatonnes of carbon dioxide every year. While peat bodies have typically accumulated during thousands of years, they can vanish within a few decades through drainage.

Since up to a third of the global terrestrial carbon stock is stored in peatlands, halting its decay by rewetting is a huge step towards a reduction of greenhouse gas emissions. However, given the profound changes drained peatlands have undergone over time, can we expect them to revert to a state that resembles the pristine peatland they once were? This is by no means certain: the history of decades of drainage has highly affected the soil structure and chemistry. Even after rewetting, soil properties may remain distinct from pristine sites and may no longer be hospitable to typical, highly specialized, peatland microbes. And if the typical microbes do not come back, it may be a recipe for an ecological disaster as these microbes are responsible for many key functions such as the cycling of methane, sulfur and nitrogen in interlinked oxic and anoxic conditions.

In a team of like-minded researchers from Belgium, Poland, Germany, Norway, the Czech Republic and Romania, we initiated the BiodivERsA-funded REPEAT (“Restoration and prognosis of peat formation in fens”) project to study this central question.

Photo 1: Left: Biebrza NP (Poland), a large groundwater-fed peatland system (fen) of international importance. Right: Peat soil, an important carbon and energy source for specialized microbial communities (Photo credits: Camiel Aggenbach)

To do so, we used a so-called space-for-time substitution approach and sampled existing groups of nearby undrained, drained and rewetted peatlands distributed all over Europe. Such approach assumes that if the microbial communities of rewetted peatlands are indistinguishable from those of undrained pristine peatlands, then this suggests recovery of peatland functioning by rewetting.

With this in mind, we took our camper (with mobile peat lab) on an expedition to collect peat samples all over Europe. Next, we processed the samples in the lab with state-of-the-art techniques such as next-generation sequencing.

Photo 2:  Our mobile peat lab (Photo credit: Franziska Tanneberger)

Our results clearly showed what we had always suspected, but until now had never been able to prove: typical peatland microbes do find their way back after rewetting, but only in those peatlands that still have a large and remnant high-quality carbon stock. In sites where decades of drainage has resulted in an irreversible loss of most of the high-quality peat, different microbial communities take over after rewetting, which may eventually compromise peatland functioning. Just like some human beings, it thus seems that peatland microbes are picky eaters that prefer a Michelin-starred restaurant over a fast-food chain.

Our corresponding paper can be read here: HERE

More info on the REPEAT project can be found here: HERE

Willem-Jan Emsens

Postdoctoral researcher, Antwerp University

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