Radial oxygen loss by the cushion plant Eriocaulon schimperi prevents methane emissions from an East‐African mountain mire

Abstract

Groundwater-fed fens are known sources of methane (CH ) emissions to the atmosphere, and these are known to be mediated by the vegetation. In a fen located in the Bale Mountains, Ethiopia, we assessed the effects of a cushion plant (Eriocaulon schimperi) and a sedge (Carex monostachya) on rhizosphere biogeochemistry. Methane and CO concentrations and pH were measured in pore-water at different depths in the profile. Redox potentials and NaCl-extractable element concentrations were analysed in soil samples from sites dominated by either E. schimperii or C. monostachya. Nutrient and element concentration were analysed in plant tissues. At Carex-dominated sites, CH concentrations increased from 70 μmol·l at a depth of 10 cm to 130 μmol·l at a depth of 100 cm. CH concentrations at Eriocaulon-dominated sites were almost zero (<1 μmol·l ) to a depth of 100 cm. Simultaneously, soil redox potentials and CO concentrations were higher at Eriocaulon-dominated sites, indicating a low potential for CH production and a high potential for CH oxidation. Eriocaulon schimperi displayed a root investment strategy to cope with the harsh environment, similar to the cushion plant Astelia pumila in Patagonian bogs. This strategy is characterised by high root/shoot ratios, high root porosity and density under high redox conditions. Both cushion plant species create an aerobic rhizosphere through radial oxygen loss from deep roots, which strongly reduce CH fluxes to the atmosphere.

Zero to moderate methane emissions in a densely rooted, pristine Patagonian bog – biogeochemical controls as revealed from isotopic evidence

“…These findings agree with previous research by Fritz et al (2011), who observed CH 4 emissions from Astelia lawns at a low magnitude compared to that presented here and presented a similar CH 4 concentration depth profile. Extremely low CH 4 concentrations have also been obtained by Dullo et al (2017) in upper peat layers of an Ethiopian cushion bog. Nevertheless, in deep peat layers below the rhizosphere, CH 4 concentrations of our study approached magnitudes reported for Chilean bogs with mixed vegetation consisting of Sphagnum mosses and A. pumila (Broder et al, 2015).…”

“…Soil-atmosphere CH 4 fluxes were calculated from the gas concentration increase over time within the chamber using the software package (MATLAB Release R2015a) routine described in Eckhardt and Kutzbach (2016) and Kutzbach et al (2007). Gas concentration was modelled as either a linear or exponential function of time.…”

“…The vascular plants, for instance of the genus Astelia (Asteliaceae), Donatia (Stylidiaceae) or Oreobolus (Cyperaceae), independently developed a cushion life form to protect from harsh climate in cold environments (Gibson and Kirkpatrick, 1985;Boucher et al, 2016). Bogs dominated by cushion-forming vascular plants (hereafter termed cushion bogs) can be found in many (mostly southern) parts of the world, for instance all along the high Andes (Coombes and Ramsay, 2001;Benavides et al, 2013;Fonkén, 2014) down to southernmost Patagonia (Ruthsatz and Villagran, 1991;Heusser, 1995;Kleinebecker et al, 2007;Grootjans et al, 2014), in the highlands of eastern Africa (Dullo et al, 2017) as well as in New Guinea (Hope, 2014), New Zealand, andTasmania (Gibson andKirkpatrick, 1985;Ruthsatz and Villagran, 1991) and some sub-Antarctic islands (Ruthsatz and Villagran, 1991). These cushion bogs could also be regarded as extreme examples for densely rooted northern bogs that are dominated by rushes and sedges.…”

“…Furthermore, more knowledge on biogeochemical processes throughout the peat column of Astelia lawns as a model plant for cushion-forming aerenchymous plants and in other microforms is needed to extend our limited understanding of these first insights into CH 4 dynamics in cushion bogs. Despite the variety of bogs dominated by densely rooted aerenchymous plants in the Northern Hemisphere and Southern Hemisphere, there is some evidence from the latest research that very low CH 4 pore water concentrations could be a more common phenomenon in those ecosystems (Knorr et al, 2015;Dullo et al, 2017;Agethen et al, 2018). In general, promotion or suppression of CH 4 production should be determined by the ratio of root density and activity associated with O 2 release versus presence of labile root organic matter or exudates accompanied by O 2 consumption (Blodau, 2002;Agethen et al, 2018).…”

The effect of water table levels and short-term ditch restoration on mountain peatland carbon cycling in the Cordillera Blanca, Peru

“…However, in the few studies that have been carried out in intact cushion peatlands, cushion plant peatlands have been found to have very low CH4 flux rates, which has been attributed to high oxidation by cushion plant roots (Fritz et al 2011;Dullo et al 2017;Sanchez et al 2017).…”