Methane is a potent greenhouse gas, and undrained peatlands are among the most important natural sources of it. In these waterlogged ecosystems, oxygen is scarce below the surface, so microbes decomposing old plant material produce methane in the saturated peat. Once formed, the gas can reach the atmosphere along three main routes: it can diffuse through the water and soil, it can travel through the hollow internal tissues of vascular plants such as sedges, or it can build up as free-phase gas bubbles until buoyancy forces them upward in sudden releases. While the first two pathways are relatively well studied, ebullition has remained stubbornly difficult to characterize, because it is episodic, spatially patchy, and easily missed by conventional flux chambers that sample at fixed intervals.

To capture this elusive pathway, the team deployed gas traps across areas with different plant cover types in the fen, allowing bubbles rising from the peat to be collected and quantified directly. They then partitioned the ebullition contribution from chamber-based measurements of total methane flux, relating the results to soil properties, water table position, pore water methane concentrations, and plant biomass. This dual approach, pairing in situ bubble collection with flux chamber data, is one of the few ways to reliably separate the episodic bubble flux from the steadier diffusive and plant-mediated components of the total emission.

The field results revealed a clear seasonal and spatial pattern. Ebullition peaked in the warmest months of July and August and was greatest in sedge-dominated areas where the water table sat closest to the surface. That combination makes physical sense: warmer peat accelerates microbial methane production, while a shallow water table shortens the distance a bubble must travel before it can escape, reducing the chance that it dissolves or is oxidized along the way. When the researchers built statistical models incorporating soil temperature, precipitation, water table depth, and pore water methane concentrations, these variables explained 42 percent of the spatiotemporal variation in measured ebullition volume and 61 percent of the variation in ebullition methane flux. In other words, a substantial share of the variability can be predicted from a handful of routinely measured environmental parameters, which is encouraging news for anyone trying to model wetland emissions at larger scales.

Yet a considerable fraction of the variation remained unexplained, underscoring just how heterogeneous ebullition is. Previous work at other peatlands has shown that bubbles can accumulate in discrete pockets of trapped gas within the peat profile and release in bursts triggered by falling atmospheric pressure, changes in water table, or simply the gradual growth of bubbles until they exceed a critical size. The Ontario fen study adds to this picture by showing that even within a single wetland, the timing and magnitude of bubble release differ sharply among plant communities, meaning that point measurements can badly misrepresent the true flux if they do not sample across vegetation types.

To isolate the role of plants more rigorously, the researchers brought intact water-saturated monoliths from the fen into a greenhouse, where they could control conditions and observe ebullition under different vegetation cover. The greenhouse experiment produced a surprising twist. Dense sedge cover was associated with higher belowground biomass but lower concentrations of methane in the pore water and less frequent ebullition. This counterintuitive result likely reflects the complex interplay between sedges and methane dynamics: sedge roots transport oxygen into the rhizosphere, where it can fuel methane-oxidizing microbes and suppress production, while root exudates can simultaneously provide fresh carbon substrates for methanogens. The net effect observed here was that thick sedge stands actually dampened the bubble pathway, even though sedges are often associated with high overall methane emissions through their internal transport tissues.

The numbers from the greenhouse experiment highlighted how much the ebullition contribution can swing with vegetation. Across the different cover types, ebullition accounted for between 1.9 and 46.9 percent of total methane emissions, a more than twentyfold range. In the field, the researchers estimated that ebullition contributed approximately 16.4 percent of total methane emissions from the fen. That figure is too large to ignore. Many ecosystem-scale methane budgets rely on chamber measurements or eddy covariance techniques that implicitly average over episodic events, and if one in six units of methane is leaving the peat as bubbles, campaigns that fail to capture ebullition risk systematically underestimating emissions.

The findings carry particular weight for the calcareous fens that dot parts of southern Ontario and similar landscapes elsewhere. These minerotrophic wetlands, fed by groundwater rich in calcium and other ions, occupy a distinctive position in the peatland spectrum, and their hydrology is strongly shaped by the surrounding hydrogeological setting. Because fens often support lush sedge vegetation, they have frequently been treated in models as systems where plant-mediated transport dominates and bubbles matter less. The new study complicates that assumption, showing that even in sedge-rich areas, ebullition remains a meaningful emission pathway, and that dense sedge cover can actually reduce it locally while adjacent communities continue to vent methane through bubbles.

For climate modeling, the implications are twofold. First, the demonstrated predictive power of simple environmental variables suggests that ebullition could be incorporated into process-based methane models with greater confidence, using soil temperature, water table depth, precipitation, and pore water methane concentration as driving inputs. Second, the strong vegetation signal means that maps of plant community composition, which are increasingly available from satellite imagery and drone surveys, could help identify hotspots and cold spots of bubble release within a wetland. As warming accelerates methane production in northern and temperate peatlands, and as shifting precipitation regimes alter water tables, the episodic bubble pathway may become an even larger share of the total, making its accurate representation a matter of real consequence for emission projections.

The study also serves as a methodological reminder to the wetland science community. Gas traps are inexpensive and simple, yet they capture a flux component that standard chambers routinely miss or smear across sampling intervals. The researchers argue that quantifying ebullition directly in the field is essential for accurate estimation of peatland methane emissions, including from sedge-dominated areas where the bubble pathway was once thought to be negligible. As nations refine their wetland greenhouse gas inventories and restoration projects multiply across rewetted peatlands, distinguishing between methane that seeps, methane that streams through plants, and methane that erupts in bubbles will be key to knowing exactly how much warming power these carbon-rich landscapes are releasing into the atmosphere.

Subject of Research: Controls on methane ebullition as a methane emission pathway in a calcareous fen peatland

Article Title: Evaluating soil and plant controls on the contribution of ebullition to methane emission in a calcareous fen

Article References: Kangro, R. J., & Strack, M. (2026). Evaluating soil and plant controls on the contribution of ebullition to methane emission in a calcareous fen. Plant and Soil. https://doi.org/10.1007/s11104-026-09084-4

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09084-4

Keywords: methane, ebullition, peatland, fen, wetland emissions, sedge, soil temperature, water table, pore water methane, belowground biomass, greenhouse gas, Plant and Soil

Rhynchospora tenuis belongs to the Cyperaceae, a plant family famous for an unusual chromosomal arrangement known as holocentry. Unlike the monocentric chromosomes of most animals and plants, which carry a single localized centromere that anchors spindle fibers during cell division, holocentric chromosomes have kinetochore activity distributed along nearly their entire length. This means spindle microtubules can attach at many points, and fragments of broken chromosomes can still be inherited rather than lost. Holocentry is generally viewed as an evolutionary escape hatch, granting lineages that possess it tolerance against chromosome breakage and fragmentation. The new study suggests it may do something even more radical: allow the complete bypass of crossovers during meiosis without sacrificing chromosome transmission.

To understand why this is so unexpected, it helps to recall what crossovers normally accomplish. During the prolonged prophase of the first meiotic division, homologous chromosomes recognize each other, synapse along their lengths, and exchange arms. These physical links, called chiasmata, are not merely a source of genetic novelty; they are load-bearing structures. They hold homologous pairs together until the cell is ready to divide, orienting the pairs so that one copy of each chromosome goes to each pole. Experimental systems in which crossovers are eliminated, through mutations in recombination enzymes such as Spo11 or its downstream repair factors, typically suffer catastrophic consequences: univalents scatter on the spindle, chromosomes segregate randomly, gametes become aneuploid, and fertility collapses. The dogma has been that at least one crossover per homologous pair, tightly positioned and regulated, is essential for the reductional division that defines meiosis.

Rhynchospora tenuis breaks this rule. Using a combination of cytogenetic imaging, immunolocalization of meiotic proteins, and genomic analyses, the researchers documented meiotic divisions in which homologous chromosomes fail to form chiasmata yet still segregate with remarkable fidelity. Instead of relying on crossover-generated chiasmata to hold pairs together, the plant appears to exploit its holocentric architecture directly. Bipolar attachment of spindle fibers to holocentric homologs can achieve the same result that a chiasma achieves in monocentric species: the stable bi-orientation of homologous chromosomes on the division spindle and their coordinated movement to opposite poles. In effect, the chromosome itself becomes the segregation unit, and the crossover becomes dispensable.

The consequences for genetic inheritance are profound. When crossovers shuffle maternal and paternal segments along each chromosome, the alleles a gamete receives are a mosaic of both parents. When crossovers are absent, each homolog is transmitted intact, so gametes receive whole parental chromosomes unchanged. Across the entire genome, this means the genetic output of meiosis resembles what clonal, asexual reproduction would produce: offspring inherit combinations of alleles that have never been broken up by recombination. Yet the organism still goes through the full choreography of sexual reproduction, pairing homologs, executing two divisions, fusing gametes at fertilization. Sex without recombination, a combination long considered unstable or paradoxical, is realized as a functioning reproductive strategy in this sedge.

This discovery speaks directly to one of evolutionary biology’s oldest puzzles: why sex exists at all. The maintenance of recombination is usually justified by its long-term benefits, purging deleterious mutations, combining beneficial ones, and generating the variation on which selection acts. But recombination also has short-term costs, breaking up favorable allele combinations and exposing genomes to selfish genetic elements. Theoretical work has long predicted that systems suppressing recombination could enjoy transient advantages, yet most such systems, from asexual lineages to inversion heterozygotes, pay the price of meiotic dysfunction. Rhynchospora tenuis demonstrates a route around that price: recombination can be abandoned not by abandoning meiosis, but by rewiring the mechanics of chromosome segregation so that the crossover is no longer structurally necessary. Evolution, in other words, can decouple the genetic function of recombination from the mechanical demands of chromosome segregation.

The study also reframes the significance of holocentricity. Chromosome biologists have catalogued holocentric lineages across the tree of life, including plants in the Cyperaceae and Juncaceae, several groups of insects such as butterflies and moths, and various microscopic eukaryotes. In these lineages, recombination patterns are often unusual, with reduced or relocalized crossovers, and some species exhibit inverted meiosis, in which the first division segregates sister chromatids rather than homologs and the second division is reductional. The new findings suggest that these quirks are not isolated oddities but expressions of a general principle: when kinetochore activity is distributed along the chromosome, the cell gains mechanistic freedom to reorganize the meiotic program. In Rhynchospora tenuis, that freedom has been cashed in for the elimination of crossovers altogether.

The researchers back these interpretations with a suite of technical observations. Cytological markers of recombination, including foci of the DNA repair protein RAD51 and the crossover-associated protein MLH1, are drastically reduced or absent during prophase I, confirming that the molecular machinery of crossing over is not engaged even though homologs still pair. Chromosome spreads reveal synapsed homologs that separate cleanly at anaphase I despite lacking chiasmata. Fluorescent in situ hybridization with chromosome-specific probes shows that entire parental chromosomes, rather than recombined mosaics, are transmitted through meiosis. And the resulting offspring are viable and fertile, demonstrating that this recombination-free sexual cycle is not a developmental accident but a stable, heritable reproductive mode. Together, these lines of evidence rule out the possibility that crossovers occur below the detection threshold in a few sites; the plant genuinely reproduces sexually without them.

For broader biology, the implications stretch in several directions. Crop breeders, who rely on recombination to assemble favorable alleles, have long been interested in manipulating crossover rates, and understanding how a genome can function without crossovers clarifies which parts of the meiotic machinery are truly indispensable. Evolutionary biologists studying asexual lineages, many of which face long-term extinction because they cannot purge deleterious mutations, now have a living model of a lineage that occupies a middle ground: genetically clonal in its output, yet cytologically and ecologically sexual. And researchers probing the evolution of holocentric chromosomes gain a concrete example of how this architecture can unlock meiotic innovations that would be lethal in monocentric genomes. Rhynchospora tenuis, a modest sedge, has become a case study in how evolution can rebuild one of life’s most fundamental processes from the chromosome outward.

Open questions remain. It is not yet fully resolved how homologs achieve stable bi-orientation without chiasmata in molecular detail, which spindle-attachment geometries the holocentric kinetochore permits, or how frequently this mode of reproduction arises and is maintained across the sedge family and beyond. Nor is it clear what selective pressures favored the loss of crossovers in this species, whether escape from selfish elements, preservation of local adaptation, or simple historical contingency. But the central message is already firm: the coupling between sex, meiosis, and recombination is not a law of nature but a historical arrangement, one that at least one plant lineage has successfully renegotiated. Sex, it appears, can survive the loss of its most celebrated source of novelty, as long as the chromosomes themselves know where to go.

Subject of Research: Meiosis without crossovers and clonal-like sexual reproduction in the holocentric sedge Rhynchospora tenuis

Article Title: Sex without crossovers mimics clonal reproduction in Rhynchospora tenuis

Article References: Zhang, M., Castellani, M., Steckenborn, S., Majka, M., Tsipas, G., Nascimento, T., Neumann, U., Thangavel, G., Robledillo, L. A., Lux, T., Deberón, L., Pfordt, U., Campoy, J. A., Vijayan, A., Timmers, T., Sargheini, N., Marek, M., Sun, H., Hofstatter, P. G., … Marques, A. (2026). Sex without crossovers mimics clonal reproduction in Rhynchospora tenuis. Nature. https://doi.org/10.1038/s41586-026-11057-7

Image Credits: AI Generated

DOI: 10.1038/s41586-026-11057-7

Keywords: meiosis, crossovers, recombination, holocentric chromosomes, Rhynchospora tenuis, sedge, chiasmata, clonal reproduction, chromosome segregation, asexual reproduction, centromere, evolution of sex