Diurnal dynamics of oxygen and carbon dioxide concentrations in shoots and rhizomes of a perennial in a constructed wetland indicate down-regulation of below ground oxygen consumption

Stems of Phragmites australis are buffering methane and carbon dioxide emissions

Internal concentrations in the culm nodes of Phragmites australis and fluxes of methane (CH₄) and carbon dioxide (CO₂) were recorded in the treatment bed of constructed wetland (CW) with subsurface wastewater horizontal flow. Fluxes of CH₄ and CO₂ from the CW treatment bed were in ranges of 0 to 490 μmol m^-2 h^-1 and from 0 to 4499 μmol m^-2 h^-1 for CH₄ and CO₂, respectively. The highest CH₄ soil fluxes were recorded in the unvegetated coarse gravel inflow zone of the CW treatment bed. The nearby inflow zone exhibited the highest CO₂ fluxes. Internal culm node concentrations of CH₄ and CO₂ were related to oxygen (O₂) stem concentrations and environmental conditions during diurnal courses. The concentrations of CH₄ and CO₂ gases were significantly correlated and opposing O₂ concentrations. Culm node parameters and shoot density of P. australis influenced internal gas concentrations and the buffering of CH₄ and CO₂ emissions. The effect of buffering CH₄ emissions is distinctive in the outflow zone of the treatment bed and is less important in the highly polluted inflow zone of the CW. Buffering of CH₄ and partially also CO₂ emissions by stems of P. australis is a process which affects the diurnal dynamics of CH₄ and CO₂ fluxes from common reed wetlands.

Redox Heterogeneity Entangles Soil and Climate Interactions

Interactions between soils and climate impact wider environmental sustainability. Soil heterogeneity intricately regulates these interactions over short spatiotemporal scales and therefore needs to be more finely examined. This paper examines how redox heterogeneity at the level of minerals, microbial cells, organic matter, and the rhizosphere entangles biogeochemical cycles in soil with climate change. Redox heterogeneity is used to develop a conceptual framework that encompasses soil microsites (anaerobic and aerobic) and cryptic biogeochemical cycling, helping to explain poorly understood processes such as methanogenesis in oxygenated soils. This framework is further shown to disentangle global carbon (C) and nitrogen (N) pathways that include CO2, CH4, and N2O. Climate-driven redox perturbations are discussed using wetlands and tropical forests as model systems. Powerful analytical methods are proposed to be combined and used more extensively to study coupled abiotic and biotic reactions that are affected by redox heterogeneity. A core view is that emerging and future research will benefit substantially from developing multifaceted analyses of redox heterogeneity over short spatiotemporal scales in soil. Taking a leap in our understanding of soil and climate interactions and their evolving influence on environmental sustainability then depends on greater collaborative efforts to comprehensively investigate redox heterogeneity spanning the domain of microscopic soil interfaces.

The role of wetland microorganisms in plant-litter decomposition and soil organic matter formation: a critical review

New soil organic matter (SOM) models highlight the role of microorganisms in plant litter decomposition and storage of microbial-derived carbon (C) molecules. Wetlands store more C per unit area than any other ecosystem, but SOM storage mechanisms such as aggregation and metal complexes are mostly untested in wetlands. This review discusses what is currently known about the role of microorganisms in SOM formation and C sequestrations, as well as, measures of microbial communities as they relate to wetland C cycling. Studies within the last decade have yielded new insights about microbial communities. For example, microbial communities appear to be adapted to short-term fluctuations in saturation and redox and researchers have observed synergistic pairings that in some cases run counter to thermodynamic theory. Significant knowledge gaps yet to be filled include: (i) What controls microbial access to and decomposition of plant litter and SOM? (ii) How does microbial community structure shape C fate, across different wetland types? (iii) What types of plant and microbial molecules contribute to SOM accumulation? Studies examining the active microbial community directly or that utilize multi-pronged approaches are shedding new light on microbial functional potential, however, and promise to improve wetland C models in the near future.