Plant community structure mediates potential methane production and potential iron reduction in wetland mesocosms

Abstract

Abstract. Wetlands are the largest natural source of methane to the atmosphere, but factors controlling methane emissions from wetlands are a major source of uncertainty in greenhouse gas budgets and projections of future climate change. We conducted a controlled outdoor mesocosm experiment to assess the effects of plant community structure (functional group richness and composition) on potential methane production and potential iron reduction in freshwater emergent marshes. Four plant functional groups (facultative annuals, obligate annuals, reeds, and tussocks) were arranged in a full-factorial design and additional mesocosms were assigned as no-plant controls. Soil samples from the top 10 cm were collected three times during the growing season to determine potential methane production and potential iron reduction (in unamended soils and in soils amended with 200 mM formate). These data were compared to soil organic matter, soil pH, and previously published data on above and belowground plant biomass. We found that functional group richness was less important than the presence of specific functional groups (reeds or tussocks) in mediating potential iron reduction. In our mesocosms, where oxidized iron was abundant and electron donors were limiting, iron reducing bacteria outcompeted methanogens, keeping methane production barely detectable in unamended lab incubations. When the possibility of re-oxidizing iron was eliminated via anaerobic incubations and the electron donor limitation was removed by adding formate, potential methane production increased and followed the same patterns as potential iron reduction. Our findings suggest that in the absence of abundant oxidized iron and/or the presence of abundant electron donors, wetlands dominated by either reeds or tussocks may have increased methane production compared to wetlands dominated by annuals. Depending on functional traits such as plant transport and rhizospheric oxygenation capacities, this could potentially lead to increased methane emissions in some wetlands. Additional research examining the role these plant functional groups play in other aspects of methane dynamics will be useful given the importance of methane as a greenhouse gas.

Vegetation alters the effects of salinity on greenhouse gas emissions and carbon sequestration in a newly created wetland

“…However, other studies found that the presence of plants in flooded wetlands or ponds enhanced CH 4 emissions (van Groenigen et al, 2011;Andrews et al, 2013;Mozdzer and Megonigal, 2013). Our results were consistent with the latter findings, possibly because CH 4 oxidation was suppressed, leading to dominance of CH 4 transport under the anaerobic conditions that occur in flooded environments (Bhullar et al, 2013).…”

“…Many studies also showed that plants can influence the quantity of greenhouse gases emitted to the atmosphere by affecting gas production, consumption, and transport (Andrews et al, 2013;Koelbener et al, 2010;Picek et al, 2007). However, salinity factor could adjust the effects of plants on greenhouse gas emissions (Munns and Tester, 2008;Tavakkoli et al, 2011;Feng et al, 2014).…”

Characteristics and metabolic patterns of soil methanogenic archaea communities in the high‐latitude natural forested wetlands of China

“…Wetland vegetation species could also be an important factor driving the variation in methanogen community composition and methanogenesis (Andrews et al, 2013;Zhang, Liu, et al, 2018;Zhang et al, 2019). We found differences in the abundance distribution and composition of the methanogenic communities according to wetland type.…”

Effects of steel slag application on greenhouse gas emissions and crop yield over multiple growing seasons in a subtropical paddy field in China

“…When we applied 2, 4, and 8 Mg ha −1 of steel slag in our plots, there was a corresponding supply of additional Fe at a rate of 67.2, 134, and 269 kg ha −1 , respectively, mainly in the oxidised form such as Fe 2 O 3 . Given that Fe 3+ is thermodynamically more favourable alternative electron acceptor than CO 2 or acetate (Chidthaisong and Conrad, 2000), the increased availability of Fe 3+ helps to suppress the activity of methanogens, the addition of Fe 3+ increase the soil reduction capacity and becomes the main electron acceptor (Van Bodegom and Stams, 1999), and iron reducing bacteria thus tend to outcompete methanogens (Andrews et al, 2013). Moreover, in addition to reducing methane synthesis, Fe 3+ can increase existing methane oxidation and the slag porous structure increases soil microbial activity of methanotrophs.…”