Dissolved organic matter indicates changes in temperature and plant communities in peatlands

Though northern peatlands cover only 3 % of the land surface they count as one of the largest terrestrial organic C pools. This huge C pool is threatened by increasing temperatures, related microbial degradation and indirect effects of climate change leading to vascular plant dominance over sphagnum mosses and a shift from graminoids to shrubs. Effects of these changes in vegetation on peat degradation are unknown. Dissolved organic matter (DOM) as an important component of the C cycle in peatlands might be used as a sensitive indicator of enhanced peat degradation. Furthermore, peatlands are the major source of DOM in many surface waters and understanding the mechanisms of peat degradation will help to elucidate the reasons for the ongoing trends of increasing concentrations of dissolved organic carbon (DOC) in surface waters. In this study we aimed to determine effects of temperature and plant functional types (PFT: graminoids, shrubs) on amounts and composition of DOM allowing conclusions about ongoing changes in peat degradation. We selected two ombrotrophic peatlands in the Italian Alps, reflecting a temperature gradient where we manipulated the vascular plant cover by selective clipping. On the established plant functional type plots we collected DOM directly after plant removal and during the following seasons over a period of one year. Besides DOC concentrations we determined DOM composition by C-13 of DOC and UV and fluorescence spectroscopy. The short term response (2-24h) of DOM to the plant clipping enabled us to estimate the C input of vascular plants via roots. The medium to long term data showed a clear relation of DOM to the temperature gradient and the PFT. All in all our results indicated a substantial contribution of the roots from vascular plants to DOM in peatlands. The release of DOM from peat clearly increased with temperature and vascular plant biomass. The difference between graminoids and shrubs seems to be marginal. We conclude that higher temperatures and greater vascular plant biomass result in increasing peat degradation as one likely reason for increasing DOC concentrations in many surface waters across Europe and North America

Plant functional type affects composition and degradation of peat along a temperature gradient

Peatlands, storing significant amounts of carbon (C), are extremely vulnerable to climate change. Indirect effects of climate change are projected to lead to a growing dominance of vascular plants in moss dominated peatlands with unknown effects on peat decomposition. In this study we investigated the influence of different plant functional types (moss, graminoid, shrub) on peat composition and decomposition. Peat cores (20 cm depth) and plant material (Sphagnum sp., Calluna vulgaris, Eriophorum vaginatum) of two ombrotrophic moss dominated peatlands on a temperature gradient in the Italian Alps were analyzed. Peat cores were taken under shrub and graminoid coverage at the low temperature site (Low-T-Site) and the high temperature site (High-T-Site). We used carbon to nitrogen ratios, C-13 and N-15 and pyrolysis gas chromatography/mass spectrometry (py-GC/MS) to assess the influence of vascular plants on peat composition and degradation. In these moss dominated peatlands, methoxyphenols from lignin indicated highest contribution of vascular plant material at 2-5 cm under shrub coverage and 5-12 cm depth under graminoid coverage. Increasing C-13 ratios with depth could be related to increasing peat decomposition. This increase was higher for peat cores under graminoid coverage than under shrub coverage. Furthermore, the enrichment in C-13 with depth was higher at the High-T-Site than at the Low-T-Site. More detailed effects of plant functional type on peat degradation were established using species specific pyrolysis products as e.g. methoxyphenols from lignin (marker compounds for vascular plants) and 4-isopropenylphenol reflecting degradation of the sphagnum peat matrix. Comparing depth records of these molecular parameters indicated higher peat degradation in the presence of graminoids compared to shrubs and at the High-T-Site compared to the Low-T-Site confirming conclusions from C-13 data. Consequently, plant functional types are very likely to influence peat composition and degradation especially at elevated temperatures, while the projected vegetation shifts from graminoids to shrubs should counteract increasing peat degradation with increasing temperature. Therefore, vegetation shifts in response to climate change may play a crucial role in determining peat composition and degradation

Loss of testate amoeba functional diversity with increasing frost intensity across a continental gradient reduces microbial activity in peatlands

Soil microbial communities significantly contribute to global fluxes of nutrients and carbon. Their response to climate change, including winter warming, is expected to modify these processes through direct effects on microbial functions through osmotic stress, and changing temperature regimes. Using four European peatlands reflecting different frequencies of frost events, we show that peatland testate amoeba communities diverge among sites with different winter climates, and that this is reflected through contrasting functions. We found that exposure to harder soil frost promoted species β-diversity (species turnover) thus shifting the community composition of testate amoebae. In particular, we found that harder soil frost, and lower water-soluble phenolic compounds, induced functional turnover through the decrease of large species (-68%, > 80 μm) and the increase of small-bodied mixotrophic species (i.e. Archerella flavum; +79%). These results suggest that increased exposure to soil frost could be highly limiting for large species while smaller species are more resistant. Furthermore, we found that β-glucosidase enzymatic activity, in addition to soil temperature, strongly depended (R2 = 0.95, ANOVA) of the functional diversity of testate amoebae. Changing winter conditions can therefore strongly impact peatland decomposition process, though it remains unclear if these changes are carried–over to the growing season

The Effects Of N, P And Crude Oil On The Decomposition Of Spartina Alterniflora Belowground Biomass

We conducted a laboratory experiment to examine how the decomposition of particulate belowground organic matter from a salt marsh is enhanced, or not, by different mixtures of crude oil, nitrogen (N), or phosphorus (P) acting individually or synergistically. The experiment was conducted in 3.8 L sampling chambers producing varying quantities of gas whose volume was used as a surrogate measure of organic decomposition under anaerobic conditions. Gas production after 28 days, from highest to lowest, was +NP = +N \u3e\u3e\u3e +P, or +oil. The gas production under either +P or +oil conditions was indistinguishable from gas production in the control chamber. Nitrogen, not phosphorus, or +NP, was the dominant factor controlling organic decomposition rates in these experiments. The implication for organic salt marsh soils is that shoreline erosion is enhanced by salt marsh oiling, presumably by its toxicity, but not by its effect on the decomposition rates of plant biomass belowground. Nutrient additions, on the other hand, may compromise the soil strength, creating a stronger disparity in soil strength between upper and lower soil layers leading to marsh loss. Nutrient amendments intended to decrease oil concentration in the marsh may not have the desired effect, and are likely to decrease soil strength, thereby enhancing marsh-to-water conversions in organic salt marsh soils

Taxonomic and functional turnover are decoupled in European peat bogs

In peatland ecosystems, plant communities mediate a globally significant carbon store. The effects of global environmental change on plant assemblages are expected to be a factor in determining how ecosystem functions such as carbon uptake will respond. Using vegetation data from 56 Sphagnum-dominated peat bogs across Europe, we show that in these ecosystems plant species aggregate into two major clusters that are each defined by shared response to environmental conditions. Across environmental gradients, we find significant taxonomic turnover in both clusters. However, functional identity and functional redundancy of the community as a whole remain unchanged. This strongly suggests that in peat bogs, species turnover across environmental gradients is restricted to functionally similar species. Our results demonstrate that plant taxonomic and functional turnover are decoupled, which may allow these peat bogs to maintain ecosystem functioning when subject to future environmental change

Phosphorus availability determines the response of tundra ecosystem carbon stocks to nitrogen enrichment.

This study was funded by NERC (NE/I016899/1) and facilitated by use of NERC facilities at Harland Huset, Ny-Ålesund and the kind support of Nick Cox and colleagues. Nancy Burns assisted with field sampling and Brodie Shaw and Rob Mills assisted with laboratory analyses. Open access via Springer Compact Agreement.Peer reviewedPublisher PD

Variation in carbon and nitrogen concentrations among peatland categories at the global scale

Publisher Copyright: © 2022 This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.Peatlands account for 15 to 30% of the world's soil carbon (C) stock and are important controls over global nitrogen (N) cycles. However, C and N concentrations are known to vary among peatlands contributing to the uncertainty of global C inventories, but there are few global studies that relate peatland classification to peat chemistry. We analyzed 436 peat cores sampled in 24 countries across six continents and measured C, N, and organic matter (OM) content at three depths down to 70 cm. Sites were distinguished between northern (387) and tropical (49) peatlands and assigned to one of six distinct broadly recognized peatland categories that vary primarily along a pH gradient. Peat C and N concentrations, OM content, and C:N ratios differed significantly among peatland categories, but few differences in chemistry with depth were found within each category. Across all peatlands C and N concentrations in the 10-20 cm layer, were 440 ± 85.1 g kg-1 and 13.9 ± 7.4 g kg-1, with an average C:N ratio of 30.1 ± 20.8. Among peatland categories, median C concentrations were highest in bogs, poor fens and tropical swamps (446-532 g kg-1) and lowest in intermediate and extremely rich fens (375-414 g kg-1). The C:OM ratio in peat was similar across most peatland categories, except in deeper samples from ombrotrophic tropical peat swamps that were higher than other peatlands categories. Peat N concentrations and C:N ratios varied approximately two-fold among peatland categories and N concentrations tended to be higher (and C:N lower) in intermediate fens compared with other peatland types. This study reports on a unique data set and demonstrates that differences in peat C and OM concentrations among broadly classified peatland categories are predictable, which can aid future studies that use land cover assessments to refine global peatland C and N stocks.Peer reviewe

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

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 longterm (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.Peer reviewe