Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Larmola, Tuula; Bubier, Jill L.; Kobyljanec, Christine; Basiliko, Nathan; Juutinen, Sari; Humphreys, Elyn; Preston, Michael; Moore, Tim R.

doi:10.1111/gcb.12328

Cited by 86 publications

(94 citation statements)

References 42 publications

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“…For comparisons of NEE between sites and with time, we used the maximum NEE defined as light-saturated at PAR levels > 1000 µmol m −2 s −1 according to a study by Larmola et al (2013). We further calculated the net exchange of CO 2 equivalents for each flux measurement.…”

Section: Environmental Variablesmentioning

confidence: 99%

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

et al. 2016

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Abstract. Ponds smaller than 10 000 m2 likely account for about one-third of the global lake perimeter. The release of methane (CH4) and carbon dioxide (CO2) from these ponds is often high and significant on the landscape scale. We measured CO2 and CH4 fluxes in a temperate peatland in southern Ontario, Canada, in summer 2014 along a transect from the open water of a small pond (847 m2) towards the surrounding floating mat (5993 m2) and in a peatland reference area. We used a high-frequency closed chamber technique and distinguished between diffusive and ebullitive CH4 fluxes. CH4 fluxes and CH4 bubble frequency increased from a median of 0.14 (0.00 to 0.43) mmol m−2 h−1 and 4 events m−2 h−1 on the open water to a median of 0.80 (0.20 to 14.97) mmol m−2 h−1 and 168 events m−2 h−1 on the floating mat. The mat was a summer hot spot of CH4 emissions. Fluxes were 1 order of magnitude higher than at an adjacent peatland site. During daytime the pond was a net source of CO2 equivalents to the atmosphere amounting to 0.13 (−0.02 to 1.06) g CO2 equivalents m−2 h−1, whereas the adjacent peatland site acted as a sink of −0.78 (−1.54 to 0.29) g CO2 equivalents m−2 h−1. The photosynthetic CO2 uptake on the floating mat did not counterbalance the high CH4 emissions, which turned the floating mat into a strong net source of 0.21 (−0.11 to 2.12) g CO2 equivalents m−2 h−1. This study highlights the large small-scale variability of CH4 fluxes and CH4 bubble frequency at the peatland–pond interface and the importance of the often large ecotone areas surrounding small ponds as a source of greenhouse gases to the atmosphere.

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Section: Environmental Variablesmentioning

confidence: 99%

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

et al. 2016

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“…Nutrients other than N have been suggested to influence N 2 fixation, especially phosphorus (P) (Vitousek and Field, 1999), which is generally the second nutrient limiting primary production (Bieleski, 1973;Vance, 2001). P limitation has been shown to play an important role in biomass growth and functioning of peatlands (Larmola et al, 2013;Hill et al, 2014;Fritz et al, 2012) and appeared to control N 2 fixation rates (Toberman et al, 2015;Vitousek et al, 2002;Chapin et al, 1991). Besides, isolated cyanobacteria were shown to be directly stimulated by P (Mulholland and Bernhardt, 2005) and, in Azolla spp., a fern species with symbiotic cyanobacteria within its leaves, P was shown to drastically increase plant growth and N content (Cheng et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth

et al. 2017

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Abstract. In pristine Sphagnum-dominated peatlands, (di)nitrogen (N 2 ) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable, and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha −1 yr −1 ), we found that diazotrophic activity (as measured by 15−15 N 2 labeling) was still present at a rate of 40 nmol N gDW −1 h −1 . This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate-rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. In addition, nitrogen fixation was found to strongly depend on light, with rates 10 times higher in light conditions suggesting high reliance on phototrophic organisms for carbon. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp. and their diazotrophic communities reveal strong differences in the optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum hosts, in which a sheltered environment apparently outweighs the less favorable environmental conditions. We conclude that microbial activity is still nitrogen limited under eutrophic conditions because dissolved nitrogen is being monopolized by Sphagnum. Moreover, the fact that diazotrophic activity can significantly be upregulated by increased phosphorus addition and acid buffering, while Sphagnum spp. do not benefit, reveals remarkable differences in optimal conditions for both symbiotic partners and calls into question the regulation of nitrogen fixation by Sphagnum under these eutrophic conditions. The high nitrogen fixation rates result in high additional nitrogen loading of 6 kg ha −1 yr −1 on top of the high nitrogen deposition in these ecosystems.

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“…Carbon decomposition was stimulated more than aboveground carbon production, leading to a net change in carbon storage. Bragazza et al (2006) and Larmola et al (2013) also observed higher CO 2 losses with nutrient amendments in Arctic tundra peats. Eggelsmann (1976) and Franzen (2006) inferred similar conclusions for peat systems in Europe, as did Harris et al (1962) for peaty wetlands reclaimed for agriculture.…”

Section: Discussionmentioning

confidence: 82%

The effects of N, P and crude oil on the decomposition of Spartina alterniflora belowground biomass

Turner

Bodker

2015

Wetlands Ecol Manage

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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 [ [ [ ?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-towater conversions in organic salt marsh soils.

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Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Cited by 86 publications

References 42 publications

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth

The effects of N, P and crude oil on the decomposition of Spartina alterniflora belowground biomass

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Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Cited by 86 publications

References 42 publications

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

Symbiosis revisited: phosphorus and acid buffering stimulate N&lt;sub&gt;2&lt;/sub&gt; fixation but not &lt;i&gt;Sphagnum&lt;/i&gt; growth

The effects of N, P and crude oil on the decomposition of Spartina alterniflora belowground biomass

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Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth