Sedge Roots Supercharge Peatland Carbon Loss by Priming Anoxic Decomposition

Peatlands are among the planet’s most powerful carbon vaults, storing more carbon than all the world’s forests combined, yet the microscopic choreography that keeps this carbon locked away has remained stubbornly opaque. A new greenhouse experiment published in the journal Biogeochemistry reveals that the roots of common wetland sedges can dramatically accelerate the breakdown of freshly deposited plant litter in oxygen-starved peat, even when those roots differ sharply in their underground architecture. The finding suggests that the living vegetation sitting atop a peatland may exert far more control over its carbon balance than previously appreciated, with implications for how these ecosystems will respond to warming, water table shifts, and restoration efforts.

The study, led by Namid Krüger of the University of Kaiserslautern-Landau together with colleagues at the University of Münster and the University of Hamburg, tackled a long-standing gap in wetland biogeochemistry. In well-aerated upland soils, scientists have documented for decades that living roots can stimulate the decomposition of soil organic matter, a phenomenon known as the rhizosphere priming effect. Roots leak sugars, organic acids, and other easily metabolized compounds into the soil, and microbes, energized by this fresh food, ramp up their consumption of older, more recalcitrant carbon stocks. But wetlands complicate this picture. In waterlogged peat, the soil matrix is not only carbon-rich but also oxygen-depleted, and wetland plants such as sedges do something unusual: they transport oxygen from their shoots down through internal air channels and release it into the rhizosphere. This means wetland roots simultaneously deliver both an energy source and the oxidant needed to break it down, a combination that could either amplify or suppress priming in ways no one had systematically tested.

To disentangle these effects, the researchers designed an elegant microcosm experiment in which two sedge species with contrasting belowground growth forms were grown on waterlogged peat containing uniformly carbon-13-labeled litter. The species, cotton-grasses of the genus Eriophorum, represent two distinct root strategies: Eriophorum angustifolium spreads through creeping rhizomes, producing a diffuse, exploratory root system, while Eriophorum vaginatum forms dense tussocks with a more compact root architecture. By labeling the litter with a rare stable isotope of carbon, the team could trace precisely how much carbon dioxide released from the microcosms came from the decomposing litter versus from other sources, using a two-end-member mixing model to partition the respiration fluxes.

The results were striking. Cumulative litter-derived carbon dioxide respiration was 87 percent higher under the rhizomatous E. angustifolium and 106 percent higher under the tussock-forming E. vaginatum than in unplanted control treatments. In other words, simply having sedge roots in the system nearly doubled the respiratory loss of carbon from the litter, regardless of which root strategy the plant employed. Yet the physical disappearance of litter told a more modest story: litterbag mass loss increased by only 10 percent under E. angustifolium and 19 percent under E. vaginatum. This mismatch between gas flux and mass loss hints that roots may be mobilizing litter carbon into microbial biomass and dissolved forms that are respired but not immediately lost from the solid litter matrix, a decoupling that could matter greatly for long-term carbon accounting.

Perhaps the most dramatic finding was the temporal trajectory of the priming effect itself. In the earliest phase of the experiment, priming effects exceeded +200 percent, meaning the planted microcosms were respiring litter carbon at more than three times the rate of the unplanted controls. Within three months, however, this fervent activity reversed, with priming effects falling below −20 percent. The researchers interpret this swing as a signature of early-stage litter decomposition dynamics. Fresh litter is initially rich in labile, water-soluble compounds that microbes devour readily once oxygen and root-derived substrates become available. As the easily decomposable fraction is exhausted, the remaining litter becomes dominated by structurally reinforced compounds such as lignin and cellulose, and the priming effect flips as root-associated microbial communities shift their enzymatic focus or as root-derived carbon begins to compete with litter carbon for microbial attention.

To visualize what was happening at the scale of individual roots, the team deployed two sophisticated imaging techniques. Zymography, a method that maps enzyme activity across the rhizosphere by pressing a fluorescently coated membrane against the soil, revealed that β-glucosidase, an enzyme that cleaves simple sugars from cellulose, was elevated around mature roots in both species. Acid phosphatase, which liberates phosphorus from organic molecules, showed an even broader pattern, elevated across the entire root system compared with background soil levels. This widespread enzymatic activation suggests that sedges do not merely fertilize the soil immediately adjacent to their root tips but create an extended zone of intensified organic matter processing that envelops the whole root architecture.

Complementing the enzyme maps, planar optode imaging allowed the researchers to watch oxygen and carbon dioxide dynamics unfold in near real time across transparent observation windows in the microcosms. This technology confirmed that the roots were actively releasing oxygen into the otherwise anoxic peat, creating ephemeral oxic hotspots where aerobic decomposition could proceed at rates impossible in the surrounding waterlogged matrix. The combination of oxygen leakage and enzyme stimulation provides a coherent mechanistic explanation for the observed priming: roots deliver the oxidant that unlocks aerobic metabolism in an anaerobic world, while their exudates and the oxygen itself fuel microbial communities that then attack the surrounding litter with renewed vigor.

What makes the study particularly consequential is the finding that both sedge species, despite their morphologically distinct root systems, produced qualitatively similar priming responses. The rhizomatous strategy, which explores soil volume widely, and the tussock-forming strategy, which concentrates roots in a dense cylinder, both enhanced litter-derived respiration by roughly the same magnitude. This suggests that the key mechanism, root oxygen loss coupled with rhizosphere enzyme activity, is a general property of these wetland sedges rather than a quirk of one growth form. For ecosystem modelers, this is both good news and a caution: it implies that priming in sedge-dominated peatlands may be reasonably represented without resolving fine-scale root architecture, but it also means that any factor increasing sedge root activity, from warming to nutrient deposition, could uniformly accelerate carbon cycling across diverse peatland types.

The broader implications reach into some of the most urgent questions in climate science. Peatlands have acted as net carbon sinks for millennia precisely because waterlogging suppresses decomposition. If living roots can double the respiratory loss of litter carbon even under anoxic conditions, then the vegetation composition of a peatland becomes a critical variable in its carbon budget. Sedges are often dominant in natural bogs and fens, and they are also among the first plants to colonize restored peatlands after rewetting. Understanding how their root activity modulates decomposition could therefore refine predictions of whether restored wetlands will regain their carbon sequestration function quickly or slowly. Moreover, as permafrost peatlands thaw and water tables fluctuate under climate change, the interplay between root-derived oxygen and priming effects may determine whether these landscapes release their ancient carbon stores as carbon dioxide or continue to bury new inputs faster than old ones decompose.

The research, supported by the German Research Foundation through its Emmy Noether programme, represents a methodological milestone as much as a conceptual one. By combining isotope tracing, enzyme imaging, and optode visualization within a single experimental framework, the team demonstrated that rhizosphere processes in wetlands can be measured with a resolution previously reserved for upland systems. The work opens the door to studying priming across a wider range of wetland plants, water regimes, and litter types, and it underscores a deceptively simple message: in the world’s waterlogged carbon vaults, the roots of living plants are quietly turning the locks. Whether that door opens wider as the climate warms is now one of the most pressing questions facing peatland science.

Subject of Research: Rhizosphere priming of litter decomposition by sedge roots in anoxic peat

Article Title: Root trait controls on rhizosphere priming effects during early-stage litter decomposition in anoxic peat

Article References: Krüger, N., Dorodnikov, M., Thomsen, S., Knorr, K.-H., & Mueller, P. (2026). Root trait controls on rhizosphere priming effects during early-stage litter decomposition in anoxic peat. Biogeochemistry. https://doi.org/10.1007/s10533-026-01373-5

Image Credits: AI Generated

DOI: 10.1007/s10533-026-01373-5

Keywords: peatlands, rhizosphere priming, litter decomposition, sedges, Eriophorum, root traits, stable isotope tracing, zymography, planar optode imaging, wetland biogeochemistry, carbon cycle, root oxygen loss