Does <i>Juncus effusus</i> enhance methane emissions from grazed pastures on peat?

Abstract

Abstract. Methane (CH 4 ) emissions from drained organic soils are generally low, but internal gas transport in aerenchymatous plants may result in local emission hotspots. In a paired-sample field study at three different sites we measured fluxes of CH 4 with static chambers from adjacent sampling quadrats with and without Juncus effusus during four field campaigns. At all three sites, CH 4 was observed in the soil at all sampling depths (5 to 100 cm), and in most cases both above and below the groundwater table. During spring, local maxima suggested methanogenesis also took place above the water table at all three sites. We found significant CH 4 emissions at all three sites, but emission controls were clearly different. Across the three sites, average emission rates (±1 SE) for sampling quadrats with and without J. effusus were 1.47 ± 0.28 and 1.37 ± 0.33 mg CH 4 m −2 h −1 , respectively, with no overall effect of J. effusus on CH 4 emissions. However, a significant effect of J. effusus was seen at one of the three sites. At this site, local CH 4 maxima were closer to the soil surface than at the other sites, and the upper soil layers were dryer. This could have affected both root CH 4 accessibility and CH 4 oxidation respectively, and together with limited gas diffusivity in the soil column, cause elevated CH 4 emissions from J. effusus. We conclude that J. effusus has the potential to act as point sources of CH 4 from drained peatlands, but more studies on the specific conditions under which there is an effect, are needed before the results can be used in modelling of CH 4 emissions.

Emissions of methane from northern peatlands: a review of management impacts and implications for future management options

“…As discussed earlier, vascular plants can play an important role in transporting CH 4 from soils to the atmosphere through aerenchyma (Couwenberg & Fritz, ; Henneberg, Elsgaard, Sorrell, Brix, & Petersen, ). The establishment of vascular vegetation following extraction is generally more extensive on cutover fens than on cutover bogs (Graf, Rochefort, & Poulin, ).…”

The Role of Management on Methane Emissions From Subtropical Wetlands Embedded in Agricultural Ecosystems

“…Plant functional groups differ in their ability to transport CH 4 with graminoids exhibiting greater internal CH 4 transport than forbs (Bhullar et al, ). At our study site, Juncus effusus (Juncus), a graminoid, is more dominant in improved/grazed wetlands than seminative wetlands (Boughton, Quintana‐ascencio, & Bohlen, ; Ervin & Wetzel, ; Gathumbi et al, ; Tweel & Bohlen, ) and is known to transport CH 4 through plant‐mediated transport directly from the production site to the atmosphere (Dalal et al, ; Henneberg et al, ; Henneberg et al, ; Petersen et al, ; Ström et al, ). While juncus is dominant in the improved and grazed wetlands, it is neither clear which species it may be replacing nor whether it can explain the higher CH 4 emissions from these wetlands.…”

The full carbon balance of a rewetted cropland fen and a conservation-managed fen

“…Low emissions from organic grasslands would be expected due to the low water table and organic matter content (Tiemeyer et al, 2016), and emissions will be further mitigated by low CH 4 diffusion due to drainage-induced increases in soil bulk density (Nykänen et al, 1998). The observed emissions could be due to CH 4 transport through aerenchymatous tissue in Juncus plants (Henneberg et al, 2012); Juncus clumps have sometimes been observed to act as point-source emissions of CH in drained peatlands (Henneberg et al, 2015). Equally, the presence of Juncus may simply indicate that these collars were situated in wetter areas of the site where CH 4 emissions were more likely to occur.…”

“…large amounts of biomass removal could counteract a terrestrial CO 2 sink and result in a C source (Renou- . However, methane (CH 4 ) can still be emitted by drained soils (Hendriks et al, 2007, Henneberg et al, 2015, with implications for C and GHG budgets.…”