Changes in the structure of plant communities may have much more impact on ecosystem carbon (C) cycling than any phenotypic responses to environmental changes. We studied these impacts via the response of plant litter quality, at the level of species and community, to persistent water-level (WL) drawdown in peatlands. We studied three sites with different nutrient regimes, and water-level manipulations at two time scales. The parameters used to characterize litter quality included extractable substances, cellulose, holocellulose, composition of hemicellulose (neutral sugars, uronic acids), Klason lignin, CuO oxidation phenolic products, and concentrations of C and several nutrients. The litters formed four chemically distinct groups: non-graminoid foliar litters, graminoids, mosses and woody litters. Direct effects of WL drawdown on litter quality at the species level were overruled by indirect effects via changes in litter type composition. The pristine conditions were characterized by Sphagnum moss and graminoid litters. Short-term (years) responses of the litter inputs to WL drawdown were small. In long-term (decades), total litter inputs increased, due to increased tree litter inputs. Simultaneously, the litter type composition and its chemical quality at the community level greatly changed. The changes that we documented will strongly affect soil properties and C cycle of peatlands.

Litter quality and its response to water level drawdown in boreal peatlands at plant species and community level

Globally, a vast extent of tidal wetlands will be threatened by sea-level-rise-induced salinization. Because ferric (hydro)oxides [Fe(III)] play a crucial role in soil organic carbon (SOC) preservation, understanding the responses of the Fe-bound C pool to increasing salinity could assist in accurate prediction of the changes in C stocks in the tidal wetland soils facing imminent sea-level rise. In this study, we investigated pools of Fe-bound C and SOC, C-degrading enzyme activity, Fe species contents and Fe-cycling bacteria, and plant properties along a salinity gradient from freshwater (0.0 ± 0.1 ppt; part per thousand) to oligohaline (2.6 ± 0.6 ppt) in a subtropical tidal wetland. Overall, the belowground biomass and the content of root Fe(III) plaque (a proxy of root oxygen loss potential) rose with the increasing salinity. Along the salinity gradient, the abundance of Gallionella (Fe-oxidizing bacteria) increased, but the abundance of Geobacter (Fe-reducing bacteria) decreased. The Fe(II):Fe(III) ratios decreased as salinity increased, implying that more Fe(II) was oxidized and immobilized into Fe(III) closer to the sea. Fe sulfides contents also elevated close to sea. The co-existence of Fe(III) and Fe sulfides at the oligohaline sites implied a high spatial heterogeneity of Fe distribution. During the growing season, the SOC pool generally decreased with increasing salinity, probably due to a reduction in aboveground-C input and enhanced activity of the C-degrading enzyme. The Fe-bound C pool was positively affected by the amorphous Fe(III) content and negatively related to the activity of phenol oxidase. The Fe-bound C pool generally rose along the salinity gradient, with the importance of Fe-bound C to SOC increasing from 18% to 29%. Altogether, our findings implied that when the imminent sea-level-rise-induced salinization occurs, the total soil C stock may generally decrease, but Fe-bound C will become increasingly important in protecting the rest of the C stocks in tidal wetland soils.

Iron-bound carbon increases along a freshwater−oligohaline gradient in a subtropical tidal wetland

https://rss.onlinelibrary.wiley.com/doi/am-pdf/10.1029/2021gb007128

Association of Organic Carbon With Reactive Iron Oxides Driven by Soil pH at the Global Scale

Biotic and abiotic catalysts for enhanced humification in composting: A comprehensive review

The hydroxyl radical (•OH) is the most powerful reactive oxygen species that plays a critical role in the fate of redox-active substances Peatlands are carbon-rich ecosystems with highly reduced substances and ubiquitous redox interfaces However, little is known about the production of •OH during the reoxidation of peatlands under waterlogged conditions Here, we conduct a set of reoxidation experiments using waterlogged peat soil dominated by various vegetation species and monitored •OH production The results show that the cumulative concentrations of •OH produced within 24 h upon oxygenation of waterlogged peat samples are 307–840 mmol g−1 The main factors affecting the production of •OH include an acidic environment, abundant reduced dissolved organic matter and Fe(II) In addition, •OH production enhances laccase activity (the largest class of phenol oxidases in the soil) by 77% ~ 204% and increases soil respiration by 317% ~ 2367% during the reoxidation of the waterlogged peat samples In addition, the simulation experiments confirm that •OH can promote laccase activity directly by serving as an electron acceptor and indirectly by oxidizing substrates Both mechanisms are greater than the effect of oxygen (O2) alone on laccase activity Our results indicate a new induction mechanism for enhancing laccase activity by •OH when subjected to anoxic-oxic interface fluctuations, which is particularly important for carbon cycling in peatlands because it can break the decomposition latch and can further promote soil organic carbon mineralization

Production of hydroxyl radicals following water-level drawdown in peatlands: A new induction mechanism for enhancing laccase activity in carbon cycling

The association of organic matter with iron (Fe-OM associations) is recognized as an important stabilization mechanism for soil organic matter. Our objective was to assess the factors regulating stabilization of soil organic matter by iron in various plant-dominated peatlands, and the role of laccase in the formation of Fe-OM associations. We investigated Fe-bound OC content and related physicochemical and biochemical parameters in four plots with different successional vegetation, and a set of simulations was conducted to investigate the association of Fe and peat-derived dissolved organic carbon catalysed by laccase. Our results indicate Fe-bound OC content varies regularly with the succession gradients, and a significant positive relationship between laccase activities and Fe-bound OC content was found (R = 0.77, P < 0.05). Although laccase degradation of recalcitrant polyphenolics is related with the CO2 release from peat soils (R = 0.697; P < 0.05), the simulation results confirmed laccase can significantly promote the formation of Fe-OM association. We propose that laccase plays a unique multifunctional role in the peatland carbon cycle. That is, while laccase degrades refractory organic matter such as lignin, it may enhance carbon sequestration by promoting the formation of Fe-OM association, which is particularly effective in acidic peat environments containing abundant iron and laccase-producing fungi.

The role of laccase in stabilization of soil organic matter by iron in various plant-dominated peatlands: degradation or sequestration?

Phosphorus sorption capacity of various iron-organic matter associations in peat soils

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The role of laccase in stabilization of soil organic matter by iron in various plant-dominated peatlands: degradation or sequestration?

Phosphorus sorption capacity of various iron-organic matter associations in peat soils